Getting Started


Front Cover (1988)

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  Table of Contents (1988)
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  Conference Information (1988)
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High-speed Josephson integrated circuit technology

   S. Hasuo

Summary: The author describes recent progress in high-speed integrated circuits using niobium junctions. He briefly describes the circuit fabrication process and then introduces the modified variable threshold logic (MVTL) gate family. The lowest experimentally obtained MVTL OR-gate delay was only 2.5 ps with a power consumption of 17 mu W/gate. This gate family is used in various high-speed logic circuits, such as 8-bit shift registers, 16-bit ALUs (arithmetic logic units), and 4-bit microprocessors. The author confirmed the high-speed operation of less than 10 ps per gate on average for these circuits. A novel high-sensitivity magnetic sensor using a SQUID (superconducting quantum interference device) was also developed. It is called a single-chip SQUID magnetometer because the feedback circuit, which is operated at room temperature is a conventional SQUID system, has been integrated on the same chip as the SQUID sensor itself.
Superconducting magnetic energy storage

   W. Hassenzahl

Summary: The author presents the rationale for energy storage on utility systems, describes the general technology of SMES (superconducting magnetic energy storage), and explains the chronological development of technology. The present ETM (Engineering Test Model) program is outlined. The impact of high-T/sub c/ materials on SMES is discussed. It is concluded that SMES is marginally competitive with other storage technologies and is likely to remain so.
The status, recent progress and promise of superconducting materials for practical applications

   J.M. Rowell

Summary: The author summarizes the progress in materials science and engineering that created today's superconducting technology. He reviews the state of the technology with conventional materials by looking at two particular applications: large-scale applications involving conductors, for example, magnets; and electronics and instrument applications. The state-of-the art is contrasted with the present understanding of the high-T/sub c/ oxide materials.
CEBAF, a large scale application of superconducting RF

   A.K. Chargin

Summary: Summary form only given. The Continuous Electron Beam Accelerator Facility (CEBAF) is a 4-GeV, multipass, CW accelerator. The machine is racetrack-shaped with the linac split into two equal parts that are located in the straight sections. The recirculating magnets, which will guide the beam through four passes around the accelerating structure, are in the arc sections connecting the two linacs. At the end of the accelerator, the beam passes into the switchyard where it is guided into any of three experimental end stations. The linac consists of 418 Nb superconducting RF cavities operating at 1500 MHz to produce a high-quality beam having a 100% duty cycle with an energy spread of 10/sup -4/ and emittance of 10/sup -9/ m. A pair of high resolution spectrometers and a high-acceptance, high-energy electron spectrometer will both utilize superconducting dipoles and cos 2 theta quadrupoles.
An all-NbN time domain reflectometer chip functional above 8 K

   S.R. Whiteley, F. Kuo, M. Radparvar and S.M. Faris

Summary: Niobium nitride has a superconducting transition temperature nearly twice that of niobium. A 5-ps time-domain reflectometer chip based on NbN technology has been designed, fabricated, and tested. The circuit is operable up to 9 K. The NbN process and limitations are discussed, and present drawbacks in the junction fabrication method are pointed out. Electrical properties are discussed, the circuit operation is described, and simulations are presented that are based on model parameters extracted from device measurements. The actual output of the circuit is presented as evidence of basic functionality. This is the first demonstration of a functional high-speed circuit based entirely on a compound superconductor technology and operable at temperatures above 8 K.
Nb multilayer planarization technology for a subnanosecond Josephson 1K-bit RAM

   S. Nagasawa, Y. Wada, H. Tsuge, M. Hidaka, I. Ishida and S. Tahara

Summary: A fabrication process for a Josephson 1-kb RAM (random access memory) has been developed using a Nb multilayer planarization technology. The technology consists of an etchback technique using 2000-molecular-weight polystyrene and SiO/sub 2/ for the junction layer and wiring layers, and a tapered edge etching technique for contact between individual wiring layers. Excellent planarity, wherein level differences in all step areas were reduced to less than 1/20th of their original values, was achieved. Appropriate RAM operation with 570-ps minimum access time and 13-mW power dissipation, were confirmed.
A 4K Josephson memory

   H. Suzuki, N. Fujimaki, H. Tamura, T. Imamura and S. Hasuo

Summary: The authors describe the design and experimental performance of a 4 K*1-bit Josephson (RAM). For high-speed memory operation, the authors have developed a compact AND gate for the decoder, a high-voltage driver gate, and a capacitively coupled single-flux quantum memory cell. The 4 K memory was designed using these gates and cell and was fabricated with Nb/AlO/sub x//Nb junctions. The minimum access time was 590 ps, and the total power dissipation was 19 mW.
Josephson address control unit IC for a 4-bit microcomputer prototype

   S. Kosaka, H. Nakagawa, H. Kawamura, Y. Okada, Y. Hamazaki, M. Aoyagi, I. Kurosawa, A. Shoji and S. Takada

Summary: The authors describe the design and operation of a Josephson address control unit IC (integrated circuit), which will be used for controlling the instruction sequence of an experimental 4-bit Josephson microcomputer prototype system. The IC is composed of three sets of 7- to 10-bit-wide registers and combinational logic circuits driven by a two-phase monopolar power supply. 593 four-function logic gates have been used in the circuit and fabricated using 2.5- mu m NbN/oxide/NbN junction technology with Mo resistors and SiO/sub 2/ insulation. The operation of the circuit has been successfully tested for all the instructions which control the program sequence of the computer system.
Fabrication of S-N-S Josephson junctions of Y-Ba-Cu-O/Au/Nb thin film sandwiches

   H. Akoh, F. Shinoki, M. Takahashi and S. Takada

Summary: The authors fabricated S-N-S (superconductor-normal-superconductor) Josephson junctions which consist of Y-Ba-Cu-O/Au/Nb thin-film sandwiches with various thicknesses of the Au barrier. Due to the AC-Josephson effect, Shapiro steps are observed in the S-N-S junctions under microwave radiation. The magnetic-field dependence of the critical current shows that the junctions behave as self-field-limited Josephson junctions. From the temperature dependence of the critical current near the transition temperature of the junctions, it is found that the thickness of the Au barrier is shorter than the coherence length of Au.
Y-Ba-Cu-O/Nb Josephson tunnel junctions

   A. Nakayama, A. Inoue, K. Takeuchi, H. Ito and Y. Okabe

Summary: The authors fabricated Y-Ba-Cu-O/Au/AlO/sub x//Nb and Y-Ba-Cu-O/AlO/sub x//Nb Josephson tunnel junctions using electron-beam evaporation of Al and Nb films and natural oxidation. Sintered Y-Ba-Cu-O was used as the base electrode. Superconducting Josephson current and hysteresis of the current-voltage characteristics, which are typical features of Josephson tunnel junctions, have been observed at 4.2 K. RF-induced voltage steps at a voltage greater than 0.4 mV have been clearly observed, and RF-induced subharmonic steps have also appeared. The superconducting Josephson current was modulated by the magnetic field.
Optimization of YBCO surfaces of tunnel junctions

   J.R. Gavaler, A.I. Braginski, M.G. Forrester, J. Talvacchio and J. Greggi

Summary: It is established that in YBa/sub 2/Cu/sub 3/O/sub 7/ films prepared by annealing amorphous oxide deposits, Ba segregation in the amorphous phase and YBCO decomposition after recrystallization are the major causes of surface degradation. The authors have grown films by entirely in-situ processing in which these effects are minimized. The films were epitaxially grown on
Flux noise and flux creep in YBCO thin films

   M.J. Ferrari, M. Johnson, F.C. Wellstood, J. Clarke, P.A. Rosenthal, R.H. Hammond and M.R. Beasley

Summary: The authors used a DC SQUID (superconducting quantum interference device) to measure the low-frequency magnetic flux noise produced by thin-film rings of YBa/sub 2/Cu/sub 3/O/sub 7- delta / (YBCO) with various microstructures. Below the transition temperature T/sub c/ of the YBCO, the spectral density of the noise scales as 1/f (f is the frequency) from 1 Hz to 1 kHz. This noise generally increases with temperature and vanishes abruptly at T/sub c/. Improvements in crystalline microstructure greatly reduce the magnitude of the noise, which was lowest for a highly orientated sample with its c-axis perpendicular to the substrate. Making a radial cut to interrupt current paths around the sample ring does not significantly affect the magnitude of the noise, demonstrating that the noise arises from a local mechanism such as the thermally activated hopping of flux bundles. Flux creep was observed in one sample cooled in a magnetic field of 1 mT, and the creep rate exhibited a sharp maximum near 80 K. It is concluded that SQUIDs and flux transformers of YBCO must be fabricated from highly orientated films to obtain low noise at low frequencies.
Surface impedance studies of the high-T/sub c/ oxide superconductors

   T.L. Hylton, M.R. Beasley, A. Kapitulnik, J.P. Carini, L. Drabeck and G. Grunner

Summary: The authors briefly review results of measurements of the multimeter-wave surface impedance of ceramic, thin-film and single-crystal samples of the high-T/sub c/ oxide superconductors. The observed losses and temperature dependences do not agree with BCS (Bardeen-Cooper-Schriefer) theory. The authors discuss recent measurements of single-crystal B/sub 2/CaSr/sub 2/Cu/sub 2/O/sub x/ and the effect of the application of a perpendicular magnetic field. They consider the possibilities of intrinsic and defect mechanisms to explain the observations. In particular, they discuss the effects of weakly coupled granular films on surface impedance. It is concluded that better samples are necessary to resolve the issue of the source of the large values of the surface impedance observed thus far.
Ultrafast response of superconducting transmission lines

   J.M. Chwalek, D.R. Dykaar, J.F. Whitaker, R. Sobolewski, S. Gupta, T.Y. Hsiang and G.A. Mourou

Summary: The authors report investigations of picosecond transient propagation on normal and superconducting transmission lines and results of a variety of lines that include YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) coplanar lines, a superconducting coaxial cable, and a dielectric-matched gold-line structure. A previously developed algorithm for analyzing transient propagation was used to identify the dominant mechanisms for signal distortion in most of these cases, and the essential properties of all tested to date are summarized for a direct comparison.
A Josephson analog limiter circuit

   D.A. Petersen, D. Herbert and T. Van Duzer

Summary: The authors have designed, fabricated and successfully tested a Josephson integrated circuit that is used to limit the range of an analog input signal. The circuit consists of a single Josephson junction with a suppressed critical current. The impedance of this suppressed junction consists of the nonlinear quasiparticle resistance in parallel with the capacitance of the junction. The junction capacitance is used to advantage as one pole of a second-order low-pass filter, the other element of which is a thin-film inductor. This filter can perform the function of a slew-rate-limiting filter, at the input to a high-speed comparator. The authors fabricated individual junctions and measured their suppression characteristics and have found that a 2- mu m*4.5 mu m junction with a nominal critical current of 170 mu A can be suppressed to less than 4 mu A of critical current with a 14-mA control current. Complete limiter circuits have been fabricated and tested for both their DC and transient characteristics. Measured DC response is in good agreement with simulation, but parasitic capacitance present in the fabricated devices limited the -3 dB bandwidth to about 3.6 GHz.
Speed-limiting factors in flash-type Josephson A/D converters

   E.S. Fang and T. Van Duzer

Summary: The authors discuss the causes of speed limitations in various A/D (analog/digital) converter designs. The upper limit on bandwidth is extracted with the help of Josephson SPICE simulations. In the Josephson A/D converter circuits discussed, the dynamic properties of the SQUIDs (superconducting quantum interference devices) determine the aperture time and dictate the bandwidth. Designs for 4-bit A/D converters that show potential for bandwidths on the order of 10 GHz are described. Particular attention is given to the bit-parallel A/D converter with self-gating AND comparator and bit-parallel A/D converters with CLAM (current latching analog microcomparator) and variable-pulse peak comparators.
A flash Josephson A/D converter constructed with one-junction SQUIDs

   H. Ko

Summary: A novel approach to the construction of a flash-type Josephson A/D (analog/digital) converter is presented. Simulations show that one-junction SQUID (superconducting quantum interference device) comparators can have a greater than fivefold advantage in bandwidth over the two- or three-junction SQUIDs in an A/D circuit. Assuming a Nb junction technology, the simulations show that a 6-bit A/D converter using one-junction SQUID comparators could have a sampling rate of approximately 20 GHz with approximately 5 bits of resolution for a 5-GHz input signal. Detailed analysis and simulations of an A/D converter constructed with one-junction SQUIDs are presented. Further improvement can be made by using a coding algorithm which requires 2N-1 comparators, instead of N, for an N-bit A/D converter.
A variable hysteresis aperturing method for superconducting counting A/D conversion

   G.S. Lee

Summary: The authors present an aperturing method for superconducting counting A/D (analog/digital) converters. The scheme, called TRAP (time release after aperturing of pulses), utilizes a large beta /sub L/ two-junction SQUID (superconducting quantum interference device) quantizer and plays on the ability to control the amount of hysteresis available in such a SQUID. Incoming information from the analog signal can be either immediately processed by the quantizer or trapped and outputted at a later time. The author explains how this control can be used to form a picosecond aperture for counting A/D converters, eliminating pulse-skipping problems. SPICE simulations confirm the ideal behaviour of the TRAP.
An on-chip superconducting clock with two modes

   G.S. Lee, A.H. Silver and R.D. Sandell

Summary: A superconducting clock based on a 2-junction SQUID (superconducting quantum interference device) flip-flop with feedback is presented. The feedback consists of transmission lines that emanate from and return to the SQUID; the entire clock is built as a compact integrated circuit. The period of the clock is mainly determined by the length of transmission line, and there are two modes of operation that can be separately excited whose periods are in a ratio of 2:1. I-V data for a pair of clocks with different designed periods confirm the presence of the two modes, show how period depends on length, and give information on the switching time of the SQUID flip-flops. Specifically, the I-V data show that there exist both a fundamental model for flux bias at odd multiples of Phi /sub 0//2 (half-flux quantum) and a doubled mode with precisely half the period flux bias at even multiples. Clocks with longer transmission lines have longer periods, but simple scaling does not occur due to other sources of time delay.
Josephson shift register design and layout

   J.X. Przybysz, R.D. Blaugher and J. Buttyan

Summary: Integrated circuit chips were designed and fabricated, based on a Josephson shift register circuit that simulated operation at 25 GHz using the SPICE program. The 6.25-mm/sup 2/ chip featured a twelve-gate, four-stage shift register fabricated with Nb/AlO/sub x//Nb Josephson junctions with a design value of 2000 A/cm/sup 2/ critical current density. SUPERCOMPACT, a general program for the design of monolithic microwave integrated circuits, was used to model the effects of layout geometry on the uniformity and phase coherence of logic gate bias currents. A layout geometry for the superconductive transmission lines and thin-film bias resistors was developed. The original SPICE-designed circuit was modified as a result of these calculations. Modeling indicated that bias current variations could be limited to 3% for all possible logic states of the shift register, and phase coherence of the gates could be maintained to within 2 degrees at 10 GHz. The fundamental soundness of the circuit design was demonstrated by the proper operation of fabricated shift registers.
A fast Josephson SFQ shift register

   F. Kuo, S.R. Whiteley and S.M. Faris

Summary: A Josephson SFQ (single flux quantum) shift register circuit operating under a two-phase power was designed and tested. The test cell was fabricated using the Nb/AlO/sub x//Nb junction SNEAP process. The main data latch is DC biased; the data storage is accomplished by the transfer of a single flux quantum in or out of a SQUID (superconducting quantum interference device) superconducting loop. A two-phase sinusoidal clock with offset is used to operate the circuit. Simulations verify that the operating frequency can go beyond 70 GHz, with operating margins exceeding 20%. Preliminary measurements indicate that the circuit operates as intended.
A novel ternary logic circuit using Josephson junction

   M. Morisue, K. Oochi and M. Nishizawa

Summary: A novel Josephson complementary ternary logic (JCTL) circuit is described. This fundamental circuit is based on the combination of two SQUIDs (superconducting quantum interference devices), one of which is switched in the positive direction and the other in the negative direction. The JCTL can perform the fundamental operations of AND, OR, NOT, and Double NOT in ternary form. The principle of the operation and design criteria are described in detail. Simulation results show that reliable operation of these circuits can be achieved with a high performance.
A Josephson ternary associative memory cell

   M. Morisue and K. Suzuki

Summary: The authors describe a three-valued content-addressable memory cell using a Josephson complementary ternary logic (JCTL) circuit. The memory cell can perform the operations of searching, writing and reading in the ternary logic system. The principle of the memory circuit is illustrated in detail by using the threshold characteristics of the JCTL. Computer simulations were performed to investigate how high-performance operation can be achieved. Simulation results show that the cycle time of memory operation is 120 ps, power consumption is about 0.5 mu W/cell, and tolerances of writing and reading operation are +or-15% and +or-24% respectively.
Quantum flux type logic circuits utilizing Josephson junction transmission lines

   M. Morisue, M. Satoh and K. Araki

Summary: A quantum-flux-type logic circuit is proposed which is composed of Josephson junction transmission lines, along which localized magnetic flux can propagate. By choosing bias current properly, the duplication of magnetic flux and a variety of logical functions can be obtained without changing the circuit topology. Computer simulation results are presented on AND and OR operations with two and three inputs for the same circuit topology, confirming that these circuits can be used as logic circuits. The simulations demonstrate the high-speed operation and low power consumption of this circuit.
RSFQ logic arithmetic

   O.A. Mukhanov, S.V. Rylov, V.K. Semonov and S.V. Vyshenskii

Summary: Several ways to achieve local timing of Josephson-junction RSFQ (rapid single flux quantum) logic elements are proposed. Several examples of serial and parallel pipelined arithmetic blocks using various types of timing are suggested and their possible performance is discussed. Serial devices enable one to perform n-bit functions relatively slowly but using integrated circuits of a moderate integration scale, while parallel pipelined devices are more hardware-wasteful but promise extremely high productivity. The possible local and self-timing of RSFQ logic elements has been demonstrated, making it possible to construct digital blocks and complex devices operating at extremely high clock frequencies, limited only by logic delays of the RSFQ elements ( approximately 100 GHz for the present-day Nb technologies).
Experimental study of the RSFQ logic elements

   V.K. Kaplunenko, M.I. Khabipov, V.P. Koshelets, K.K. Likharev, O.A. Mukhanov, V.K. Semenov, I.L. Serpuchenko and A.N. Vystavkin

Summary: New elements of the rapid single flux quantum (RSFQ) logic family have been designed, fabricated, and tested. All-Nb 14-layer 5 mu m technology using externally shunted tunnel junctions with j/sub c/=500 A/cm/sup 2/, I/sub c/R/sub s/=300 mu V, and B/sub c/
A new A/D converter with quantum flux parametron

   N. Shimizu, Y. Harada, N. Miyamoto and E. Goto

Summary: A flash-type superconducting A/D (analog/digital) converter is proposed. The basis low-frequency operation of this converter, which compromises a quantum flux parametron (QFP) and an RF SQUID (superconducting quantum interference device), has been observed. The RF SQUID consists of a Josephson junction and a load inductor which is part of the QFP. It converts an analog signal to period digital signals of one quantum flux (2.07*10/sup -5/ W-b) per cycle. The QFP works as both an amplifier and a comparator of the periodic digital signals, by adding an exciting signal. This A/D converter is expected to achieve high-speed operation of 20 GHz. Several 4-bit A/D converter circuits were fabricated, using the conventional Nb-Pb alloy process, with a junction size of 5 mu m*5 mu m and supercurrent density of 200 A/cm/sup 2/. Basic operation at 100 KHz was confirmed experimentally.
Preparation and performance of toroidal Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/-RF SQUIDs

   Y. Zhang, M. Diegel and C. Heiden

Summary: Starting from disk-shaped bulk specimens of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ with T/sub c/ near 90 K, RF SQUIDs (superconducting quantum interference devices) to toroidal topology with a permanently adjusted mill-bridge contact were prepared. Contact trimming was done by reducing the cross section so that a good SQUID signal was obtained at 77 K. The SQUIDs were sealed after the adjustment in order to prevent degradation by moisture. Using conventional 20-MHz readout electronics the SQUIDs were operated in the flux-locked loop mode. Flux noise of the order of 10/sup -4/ Phi /sub 0// square root Hz was obtained at 77 K in the white region of the spectrum, with excess noise below about 100 Hz. The devices are quite robust due to their monolithic structure and demonstrate good stability against thermal cycling.
The properties and potential applications of bulk RF SQUIDs made from YBaCuO, BiSrCaCuO and TlCaBaCuO

   C.M. Pegrum, J.R. Buckley and M. Odehnal

Summary: The authors have developed methods for making RF SQUIDs (superconducting quantum interference devices) from bulk samples of high-temperature ceramic superconductors. The technique relies on intrinsic closed superconducting pathways within the material to form the SQUID loop, and intergrain contact to provide the necessary Josephson elements. The material does not need to be multiply connected (for example, ring-shaped) or to have a region which is deliberately weakened or constricted. In this sense this type is quite unlike other RF SQUIDs that have been developed recently, which use break junctions or have machined constrictions. It is also much simpler to make and reveals some interesting properties related to the nature of the contact between grains. The authors conclude that a very simple system can make a magnetometer with a field sensitivity at 77 K of 1.5*10/sup -10/ T-Hz/sup -1/2/, comparable to that of a flux gate magnetometer. The technique also provides a good educational demonstration of quantum interference and can be used for detecting the superconducting state in small bulk samples.
Noise measurements in a 2-hole radio frequency SQUID at liquid nitrogen temperature

   S.P. Harrop, M.S. Colclough, C.E. Gough, M.N. Keene and C.M. Muirhead

Summary: The authors report measurements of the noise in a two-hole RF SQUID (superconducting quantum interference device) fabricated from bulk YBCO by an erosion technique in the frequency range 30 mHz to 1 kHz. Above 100 Hz the noise is essentially white with an RMS (root mean square) value of 5*10/sup -4/ phi /sub 0// square root Hz and is dominated by noise from the electronics. Below 10-Hz the noise power rises as 1/f/sup 0/9/.
High T/sub c/ RF-biased SQUID

   C.H. Harmston, O.G. Symko, W.J. Yeh, D.J. Zheng and S.K. Kulkarni

Summary: Results are presented on the behaviour of a simple RF-biased SQUID (superconducting quantum interference device) made out of YBa/sub 2/Cu/sub 3/O/sub 7/. It consists of a fractured ceramic pellet stuck together at room temperature. This simple device is shielded by a high-T/sub c/ tube and shows the characteristic flux quantization behaviour up to 77 K. At 4.2 K its magnetic flux resolution is less than 2*10/sup -4/ phi /sub 0// square root Hz, and it shows sensitivity degradation as the temperature is raised.
Properties of the microwave SQUID with an YBaCuO point contact junction

   T. Ryhanen and H. Seppa

Summary: A high-sensitivity microwave SQUID (superconducting quantum interference device), suitable for RF attenuation measurements, is constructed taking advantage of the low density of states of current carriers in high-T/sub c/ materials. The dynamics, the noise properties, and the sensitivity of the microwave SQUID are theoretically analyzed. The ultimate energy resolution of the waveguide SQUID is inversely proportional to the characteristic frequency omega /sub c/=R/sub q//L of the loop. omega /sub c/ is high for YBaCuO junctions at 4.2 K because of small leakage. A flux sensitivity of 4*10/sup 4-6/ phi /sub 0// square root Hz has been achieved, which is in good agreement with the theoretical predictions.
Josephson junction and DC SQUID made from superconducting Y-Ba-Cu-O thick film

   A.Z. Lin, H.Q. Li, L. Tang and F.W. Liu

Summary: YBa/sub 2/Cu/sub 3/O/sub 7-x/ thick films were fabricated by the method of screen printing. A zero-resistance state was achieved at 90 K. The highest critical current density was about 150 A/cm/sup 2/ at 77 K. A bridge-type Josephson junction and DC SQUID (superconducting quantum interference device) were fabricated from thick films and operated at 77 K. The induced steps produced by the AC Josephson effect were observed on the I-V (current voltage) curve when microwave radiation was applied to the junction. The clear periodic patterns of a DC SQUID are observable at 77 K. Environmental protection and the stability of thick films and devices are discussed.
DC SQUID in YBaCuO ceramics operating at 77 K

   M.L.C. Sing, D. Robbes, Y. Monfort, D. Bloyet, J. Provost and B. Raveau

Summary: Constrictions with typical cross-sectional areas of 10/sup -8/-10/sup -7/ m/sup 2/ engraved in bulk YBa/sub 2/Cu/sub 3/O/sub 7-d/ ceramics operate as DC SQUIDs (superconducting quantum interference devices) at 77 K. These sensors have a magnetic field sensitivity of 1 to 20 pT/ square root Hz, a flux sensitivity of 6*10/sup -6/ to 3*10/sup -5/ phi /sub 0// square root Hz, and a corresponding energy resolution in the 10/sup -30/-10/sup -29/ J/Hz range around 20 kHz. The noise spectral density of the device clearly exhibits low-frequency 1/f noise, which scales throughout the whole investigated range of frequencies. The noise spectra at 1 Hz varies between 5*10/sup -27/ and 2*10/sup -26/ J/Hz.
DC SQUIDs fabricated with YBaCuO thin films

   S. Wang, G. Cui, Y. Dai, H. Jiang, X. Zeng, J. Li, Z. Bao, C. Li, D. Yin, K. Shao and C. Cao

Summary: DC superconducting quantum interference devices (SQUIDs) have been fabricated from thin films of YBaCuO. The devices were made by the photolithographic method with wet etching. The oscillatory output voltage of the devices in a sweeping magnetic field is shown to have a good periodicity. Triangular wave patterns of the DC SQUID output were observed.
A novel HTS magnetometer, exploiting the low jc of bulk YBCO

   J.C. Gallop, S. Lilleyman, C.D. Langham, W.J. Radcliffe and M. Stewart

Summary: The authors report a novel form of magnetometer which is based on the low critical magnetic field H/sub c1/ of sintered samples of the high-temperature ceramic superconductor YBa/sub 2/Cu/sub 3/O/sub y/. By driving a sample of the superconductor around a magnetization hysteresis loop at a frequency of approximately 100 kHz and detecting the induced voltage in a coil coupled to the sample at the second harmonic of the drive frequency, they find that this voltage is linearly dependent on the applied DC magnetic field in which the sample is situated. They present a model which explains the operation of this magnetometer. The device, while not sensitive as a SQUID (superconducting quantum interference device), has the advantage of a wider dynamic range and direct measurement of flux density unlike a SQUID, which is only capable of sensing flux density changes. When operated at 77 K the prototype magnetometer has already demonstrated a sensitivity at least 10 times better than that of a commercial flux-gate magnetometer. The system also appears to provide a simple method for investigation of flux flow in these materials.
Memory characteristics of ring-shaped ceramic superconductors

   A. Takeoka, M. Hasunuma, S. Sakaiya, T. Hirano and Y. Kuwano

Summary: The authors investigated the residual magnetic field characteristics of ring-shaped ceramic superconductors in a Y-Ba-Cu-O system with high T/sub c/. The residual magnetic field of a ring with asymmetric current paths, supplied by external currents, appeared when one of the branch currents was above the critical current. The residual magnetic field saturated when both branch currents exceeded the critical current of the ring and showed hysteresis-like characteristics. The saturated magnetic field is subject to the critical current of the ring. The time constant of the persistent current in a ring, evaluated from the damping coefficient, was 5000 hours at most. A superconducting ring with asymmetric current paths suggests a simple, novel persistent-current-type memory device.
Three-dimensional flux-sensor composed of high-T/sub c/ superconductor

   S. Nishijima, K. Takahata, T. Okada, H. Okushiba, Y. Nagamori, S. Okamoto and K. Hayashi

Summary: A three-dimensional flux sensor has been studied with the aim of realizing a practical application of high-T/sub c/ oxide superconductor Y-Ba-Cu-O. Thick-film and cylindrical sensors were made and examined. The current-voltage characteristics were investigated as a function of magnetic field at liquid nitrogen temperature. The flux flow was observed in a wide range of magnetic fields from 0.001 to 1 Tesla, and the magnetic field could be evaluated by the output voltage. The dependence of the voltage on the angle between the current and magnetic field direction was also examined. The flux flow was affected by the direction of the external magnetic field, resulting in a change of the output voltage. The output voltage was found to show hysteresis with respect to the external field. On the basis of these phenomena, a three-dimensional flux sensor was designed and fabricated.
Millimeter-wave detection by GBJJ using high-T/sub c/ superconducting YBaCuO films

   S. Kita, H. Tanabe and T. Kobayashi

Summary: Millimeter-wave detection in the heterodyne mixing mode has been carried out using the high-T/sub c/ superconducting GBJJ (grain boundary Josephson junction). The GBJJ was fabricated from high T/sub c/ superconducting Y-Ba-Cu-O films, prepared on YSZ and SrTiO/sub 3/ substrates using an RF sputtering technique. The junction was patterned by chemical wet etching with phosphoric acid solution. The authors carried out experiments in the heterodyne mixing mode for a signal of 35 GHz with local oscillation at 34.97 GHz. The detected IF (intermediate frequency) output power was obtained at a bias voltage lying midway between the zeroth and first Shapiro steps. A mixer conversion efficiency of -15 dB was obtained with a dynamic range of about 20 dB at 35 GHz. This result strongly implies that high-T/sub c/ superconducting GBJJ works well as a detector at millimeter-wave frequencies.
Josephson harmonic mixing and internal oscillation-mixing in YBCO superconducting weak link at liquid nitrogen temperatures

   J. Song, P.H. Wu, Q.H. Cheng, S.Z. Yang, J. Chen, D. Jin, H.X. Luo and J.S. Kui

Summary: Using a superconducting weak link (bridge) made of YBCO, the authors have successfully observed Josephson harmonic mixing between a local oscillation (LO) at X band and a signal at Ka band. Specifically, fourth-order harmonic mixing between 35.47 GHz and 8.843 GHz was observed. For a given signal level, the IF (intermediate frequency) responses depended strongly on both LO level and DC voltage bias across the junction. For zero bias, there is still IF output which is characteristic of even-order harmonic mixing. When the LO power level is such that the zero voltage current is suppressed to the second zero, the IF responses are maximum if the junction is biased between the zeroth and first steps induced by the LO. Also studied is the internal oscillation-mixing. An incoming signal at either X or Ka band gives rise to IF signal peaks if the junction is biased at voltages such that the corresponding internal Josephson frequencies are equal to, or harmonics of, the incoming signal frequency.
Heights of microwave induced steps, temperature dependent supercurrent and other experimental observations in YBCO weak link

   N.X. Shen, P.H. Wu, S.Z. Yang, Q.H. Cheng, Y.B. Sheng, H.X. Luo and J.S. Kui

Summary: For YBCO bridges made of bulk samples, the authors have carefully measured the height of the microwave-induced steps as a function of applied microwave power and found, for Omega =hf/2eI/sub c/R=0.25, approximate agreement with the Bessel function dependence. The supercurrent versus temperature dependence follows the I/sub c/ varies as (1-T/T/sub c/) relationship quite closely at temperatures far from T/sub c/, while in the vicinity of T/sub c/ the deviation from it can be pronounced. For bridges made of YBCO thin films, the temperate-dependent supercurrent can be expressed as I/sub c/ varies as (1-T/T/sub c/)/sup 3/2/. Also discussed are some possible explanations of experimentally observed I-V curves which might be attributed to mechanisms such as self-heating and junctions in series.
Properties of lift-off structured high T/sub c/ microbridges

   B. Hauser, B. Klopman, D. Blank and H. Rogalla

Summary: Microbridges and DC SQUIDs (superconducting quantum interference devices) were fabricated, using a lift-off technique, from RF sputtered YBaCuO films on MgO single-crystal substrates. Microwave measurements at 9 GHz on microbridges and the magnetic-field dependence of their critical current reveal wide bridge behaviour up to temperatures near the maximum operating temperature of the bridge. Mostly, a linear dependence of the critical current on the temperature is found, which is connected with high intrinsic 1/f noise if the bridge is constant-current-biased slightly above the critical current. In some bridges and DC SQUIDs, regimes with a temperature dependence proportional to (1-T/T/sub c/)/sup 1.5/ are found. In this case the 1/f noise level is much smaller and SQUID modulation can be followed to about 65 K.
Grain boundary Josephson devices by YBaCuO films and 77 K operations

   T. Yamashita, A. Kawakami, S. Noge, W. Xu, M. Takata, T. Komatsu and K. Matusita

Summary: Magnetron sputtering and screen printing methods were used to fabricate YBaCuO films with thicknesses of 5 to 30 mu m. The annealing of the films at 1000 degrees C gave abnormal grain growth. The grain size of the films was about 2 to 70 mu m. With photolithography and razor cutting techniques, the films were formed into bridge-type Josephson junctions having a few grain boundaries in the bridge regions. In the devices, clear Shapiro steps and SQUID (superconducting quantum interference devices) patterns were observed at 77 K. The experiments showed that all currents flowing through grain boundaries are Josephson currents in YBaCuO polycrystalline films. Clear Josephson effects were observed in about 30% of the fabricated devices. Such devices may have high potential for high-frequency detectors and SQUID flux sensors operative at 77 K.
Three terminal YBaCuO Josephson device with quasi-particle injection gate

   T. Kobayashi, K.-I. Hashimoto, U. Kabasawa and M. Tonouchi

Summary: A novel type of three-terminal Josephson device called the SCST (superconducting current switching transistor), was fabricated using high-T/sub c/ LnBaCuO (Ln=Y, Er) thin epitaxial and/or polycrystalline films. The hot quasi-particle injection effect on the Josephson (or superconducting) current in the films was closely examined. The zero bias drain current was efficiently suppressed by the injection of the hot quasi-particles through the gate electrode. A comparison of the experimental results and analyses based on the BCS theory suggests that the main mechanism of the current modulation is the nonequilibrium superconductivity due to the accumulation of the excess quasi-particles. The maximum current modulation gain was 5 approximately 7 and the modulation current ranged as low as 3 approximately 10 A/cm/sup 2/.
Growth, patterning, and weak link behaviour in high T/sub c/ thin films

   G.C. Hilton, R.A. Schweinfurth and D.J. Van Harlington

Summary: The authors report techniques for making Josephson weak links in thin films of the high-temperature ceramic superconductors. They have fabricated superconducting thin films of YBaCuO and BiSrCaCuO by several methods. These films have been patterned into fine lines and small loops, and a variety of measurements have been performed on these structures, Intrinsic weak link behaviour is observed between grains in patterned films and can be modified by an in-situ ion beam milling and measurement procedure.
Laser patterning of YBaCuO weak link bridges

   E. Wiener-Avnear, J.E. Cooper, G.L. Kerber, J.W. Spargo, A.G. Toth, J.Y. Josefowicz, D.B. Rensch, B.M. Clemens and A.T. Hunter

Summary: A laser ablation process was developed to pattern thin-film superconducting devices with 1- mu m resolution. The process was utilized to fabricate bridge structures in high T/sub c/(>90 K) YBaCuO superconducting thin films sputtered on various substrates. For bridges patterned on thin films with a high degree of polycrystallinity, the authors observed weak-link Josephson behaviour, from 4.2 K up to T/sub c/. The weak-link behaviour was attributed to grain-boundary superconducting tunneling. The results suggest that direct laser patterning can be a powerful technique for evaluation and optimization of prototype superconducting devices.
Josephson junctions with bulk YBa/sub 2/Cu/sub 3/O/sub 7-x/, Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ and Tl/sub 2/Ca/sub 2/Ba/sub 2/Cu/sub 3/O/sub 10+x/

   W. Eidelloth, F.S. Barnes, S. Geller, K.Y. Wu, Z.Z. Sheng and A.M. Hermann

Summary: The characteristics of point contacts with combinations of Pb, YBa/sub 2/Cu/sub 3/O/sub 7-x/, Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/, (YBCO), (BSCCO), and Tl/sub 2/Ca/sub 2/Ba/sub 2/Cu/sub 3/O/sub 10+x/ (TCBCO) have been measured in a shielded liquid helium dewar. Zero-voltage currents were found in all arrangements; diffraction patterns in the voltage-flux curves were observed with all materials. Electron pairs were confirmed as carriers in all investigated high-T/sub c/ materials. All junctions resembled weak-link bridge structures rather than tunnel junctions. Despite strong shunting, hysteresis was found in the I-V curves of some point contacts. A structure of unknown origin was found in the I-V curves of YBCO-BSCCO junctions. Both YBCO-YBCO and BSCCO-BSCCO junctions had much lower normal resistances and considerably higher critical currents than YBCO-BSCCO point contacts. The reason for this phenomenon is not yet understood.
Josephson effect and macroscopic quantum interference in high-T/sub c/ superconducting thin-film weak links at 77 K

   A.I. Golovashkin, A.L. Gudkov, S.I. Krasnosvobodtsev, L.S. Kuzmin, K.K. Likharev, Y.V. Maslennikov, Y.A. Pashkin, E.V. Pechen and O.V. Snigirev

Summary: The authors studied the properties of single and double superconducting weak links (Dayem microbridges) fabricated by direct photolithography from thin films of 1-2-3 copper oxides, deposited on SrTiO/sub 3/ and LiNbO/sub 3/ substrates by laser sputtering of ceramic targets. Values of critical current I/sub c/ and normal resistance R/sub n/ of the weak links could be altered by plasma etching of the structures. I/sub c/R/sub n/ products up to 100 mu V were achieved, and well-pronounced Shapiro steps under 8-GHz microwave radiation were observed at 77 K. Macroscopic quantum interference was clearly registered in double microbridge structures at the same temperature.
Metal-oxide ceramic RF SQUID operating at 77 K

   V.M. Zakosarenko, E.V. Ilyichyov and V.A. Tulin

Summary: The authors fabricated several versions of Zimmerman-type RF SQUIDs (superconducting quantum interference devices) from bulk ceramic YBa/sub 2/Cu/sub 3/O/sub x/ samples and studied their characteristics. The SQUIDs operated reliably at liquid nitrogen temperature and proved to be stable over time. Some of their properties were similar to those of RF SQUIDs based on conventional superconductors, but there were also some major distinctions. The latter may be due to the fact that because of the macroscopic size of the weak link, the magnetic flux vortex enters reversibly (without respect to the RF current) the body of the weak link without crossing it. One of the SQUIDs operated as a conventional nonhysteretic SQUID, but the small value of the critical current of the weak link led to a lower operating temperature (T
Microlithography of high-temperature superconducting films: laser ablation vs. wet etching

   P.H. Ballentine, A.M. Kadin, M.A. Fisher, D.S. Mallory and W.R. Donaldson

Summary: Narrow lines and microbridge structures have been etched in sputtered superconducting films of Y-Ba-Cu-O by variations of two methods. The first uses standard photolithography followed by wet etching in weak acid. The second uses a maskless process involving focused pulsed YAG (yttrium-aluminium-garnet) laser together with a computer-controlled x-y stage to produce local ablation of the superconducting film. Issues relating to limits of resolution, annealing of films, and degradation of superconducting properties are critically discussed for the two approaches.
Single superconducting thin film devices for applications in high T/sub c/ materials circuits

   G.K.G. Hohenwarter, J.S. Martens, D.P. McGinnis, J.B. Beyer, J.E. Nordman and D.S. Ginley

Summary: The authors investigated several different devices based on regions of weak superconductivity and multiple parallel links in thin films. Devices were fabricated with Nb and YBa/sub 2/Cu/sub 3/O/sub 7-x/ films. Hysteretic symmetric and asymmetric I-V (current-voltage) curves have been observed. Flux flow was indicated. Device switching properties and the dependence of the flux-flow signature in the I-V curve on applied magnetic field were explored. Contrary to vortex flow devices based on Josephson junctions, the devices described here do not possess a tunnelling barrier and are made of only a single superconducting layer. Hence they should be applicable to electronic circuits based on high-T/sub c/ superconducting materials without the need for tunnel junctions.
Germanium thin film growth onto high T/sub c/ superconducting films

   M. Tonouchi, Y. Sakaguchi, K. Hashimoto, Y. Yoshizako and T. Kobayashi

Summary: Germanium thin film growth on high-T/sub c/ superconducting films has been studied. The crystallized Ge films were prepared on YBaCuO films at a substrate temperature above 200 degrees C. An ECSA (electron spectroscopy for chemical analysis) study revealed that the Ge films were formed without intense reaction between Fe and YBaCuO.
Characterization of YBaCuO and ErBaCuO thin films deposited on silicon and gallium arsenide substrates

   D.K. Chin, T. Van Duzer, W.L. Hansen, K.M. Yu, W.F. Stickle, S.Y. Lee and B. Murdock

Summary: YBaCuO and ErBaCuO films have been deposited on Si substrates with and without a ZrO/sub 2/ buffer layer and on GaAs substrates by RF diode sputtering from stoichiometric oxide targets. The films and interface between the films and semiconductor substrates are analyzed by Rutherford backscattering spectrometry (RBS), X-ray fluorescence spectroscopy (XRF), Auger electron spectroscopy (AES), energy dispersive X-ray spectrometry (EDAX), and scanning electron microscopy (SEM). The films grown on Si substrates with a ZrO/sub 2/ buffer layer show superconductivity above 65 K, and no significant interaction at the interface is observed. High-T/sub c/ films can be obtained either by slow-furnace annealing or by rapid heat-pulse annealing. No significant interaction is observed between YBaCuO (ErBaCuO) and GaAs after rapid thermal annealing at temperatures below 750 degrees C.
High T/sub c/ thin film and device development

   K. Betts, M.B. Burbank, A. Cragg, A.A. Fife, P.R. Kubik, S. Lee, J. McCubbin, D. McKenzie, M. Tillotson, B. Taylor, H. Tran, J. Vrba, A.C.D. Chaklader, G. Roemer, B. Heinrich, J. Chrzanowski and J.C. Irwin

Summary: Thin films of the high-T/sub c/ superconductor YBa/sub 2/Cu/sub 3/O/sub y/ have been deposited on various substrates by diode and magnetron sputtering using bulk sintered targets. These films have been analyzed by a variety of methods: scanning electron microscopy, X-rays, electron beam microprobe, mass spectroscopy and Raman spectroscopy. The stoichiometries of the films have been measured as a function of the radial position from the center of the sputtered beam at a fixed target-substrate distance. Patterning of the films has been carried out to form planar structures such as strip lines, microbridges and RF SQUIDs (superconducting quantum interference devices). The DC current-voltage characteristics of the microbridges were measured as a function of temperature. RF SQUID behavior has been observed for single-loop devices and their properties established at 4.2 K and higher temperatures. Flux-locked noise spectra with a 1/f noise power response were recorded in the frequency range from 0.01 to approximately=100 Hz. RF SQUID signals have been observed for temperatures up to 55 K.
Interaction among superconducting weak links in a bulk sample of YBaCuO at 77 K

   T. Yang, L. Dong, Z.Q. Sun, X. Chen, C. Liu, J. Li, X. Wu and L. Zhou

Summary: The DC and AC Josephson effects have been directly observed for a piece of superconducting material about 5 mm*1 mm*0.2 mm which was cut from a bulk sample of Y/sub 1/Ba/sub 2/Cu/sub 3/. the I-V (current voltage) characteristics were similar to those of a microbridge. When the sample was irradiated by 35.6-GHz microwaves, about 30 Shapiro steps on the I-V curves were observed at 77 K. Microwave-induced steps at both n(hf/2e) and 2n(hf/2e) were coexistent in the sample. It was found that the step width is not always consistent with the Josephson I-V relation. This phenomenon might result from complex interaction among a variety of superconducting links in the bulk sample of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub y/.
Low frequency resistance fluctuations in films of high temperature superconductors

   P. Rosenthal, R.H. Hammond, M.R. Beasley, R. Leoni, P. Lerch and J. Clarke

Summary: Low-frequency voltage fluctuations in thin films of YBa/sub 2/Cu/sub 3/O/sub 7-x/ at and above the superconducting transition temperature have a spectral density proportional to the ratio of the average voltage across the film to the frequency. The ratio of the spectral density to the average voltage decreases markedly as the microstructure of the films is improved. In contrast to classic superconductors, the noise at the resistive transition does not arise from equilibrium temperature fluctuations.
Switching noise in YBa/sub 2/Cu/sub 3/O/sub x/ 'macrobridges'

   R.H. Ono, J.A. Beall, M.W. Cromar, P.M. Mankiewich, R.E. Howard and W. Skocpol

Summary: Intermittent switching was observed in the voltage current characteristics of thin-film bridges of YBa/sub 2/Cu/sub 3/O/sub x/. At a fixed bias point there are multiple metastable voltage states with lifetimes which depend on the bias current and applied magnetic field. The microbridges are made of thin (<500 nm) polycrystalline films of YBa/sub 2/Cu/sub 3/O/sub x/ which are patterned by liftoff into structures with dimensions ranging from less than 1 mu m. to 100 mu m. Details of the fabrication process and the measurements are presented. The results are discussed in the context of fluctuations in the effective resistance of the bridge due to motion of trapped flux.
Ultra broad band measurements on high T/sub c/ ceramic superconducting transmission lines

   K. Araki, I. Iwasa, Y. Kobayashi, S. Nagata and M. Morisue

Summary: Transmission lines were fabricated on high-T/sub c/ ceramic conductor thin films by means of a lithographic technique. A scalar network analyzer was used to perform measurements from 10 MHz to 26.5 GHz of the transmission and reflection characteristics of superconducting transmission lines at 4.2 K, 77 K, and room temperature. The lines were fabricated from 0.8- mu m-thick YBa/sub 2/Cu/sub 3/O/sub 7/ on 1.0-mm-thick SrTiO/sub 3/ substrates. Characteristic impedance, attenuation constant, phase constant, group time delay and group velocity were calculated by a novel algorithm which is processed in real time. Time domain responses, e.g., pulse delay and waveform distortion, were also easily obtained by a computer technique. The degradation due to the etching process is investigated, and a comparison is made of copper and ceramic transmission lines.
A film transmission line resonator to measure the microwave surface resistance of YBa/sub 2/Cu/sub 3/O/sub 7-x/

   J.S. Martens, G.K.G. Hohenwarter, D.P. McGinnis, J.B. Beyer and D.S. Ginley

Summary: The authors constructed microstrip transmission line resonators with YBa/sub 2/Cu/sub 3/O/sub 6.9/ ground planes, SiO dielectric, and Nb top conductors. The film resonator is a low-impedance section n lambda /2 long, and the wave is launched from a coaxial line. Loose coupling is provided by the discontinuity between 50- Omega feed lines and the 0.05- Omega resonator section. After de-embedding the transmittance data of the structure, the surface resistance of the ceramic superconductor can be computed. The surface resistance of YBa/sub 2/Cu/sub 3/O/sub 6.9/ at 4.2 K was about a factor of 60 higher than the theoretical value for Nb at 4.2 K over the range 2.9-6 GHz. The power law behavior versus frequency of the surface resistance is roughly quadratic, which is consistent with two-fluid analysis.
RF electromagnetic investigation of an YBa/sub 2/Cu/sub 3/O/sub 7/ thin film by proximity coupling

   H.P. Baum, A. Schenstrom, Y. Zheng, B.K. Sarma, M. Levy, J.H. Kang and R.T. Kampwirth

Summary: Reports an investigation of the RF electromagnetic (EM) attenuation by a YBa/sub 2/Cu/sub 3/O/sub 7/ thin film at 1 GHz as a function of temperature. An increase in the attenuation was observed as the temperature was decreased below the superconducting transition temperature T/sub c/ approximately=84 K, followed by a rapid decrease at lower temperature ( approximately 25 K). A theoretical analysis of EM absorption due to M. Fibich (1965) is evoked to explain the experimental results. It is concluded that the absorption of 1-GHz electromagnetic waves in the present experimental arrangement is determined by the real part of the conductivity in the superconducting state. This implies that even for the high-temperature superconductors considered, the Em absorption is determined by the BCS (Bardeen-Cooper-Schrieffer) coherence factor II, appropriate for electromagnetic absorption and nuclear spin relaxation, as contrasted with the factor I with opposite sign, which is appropriate for sound absorption.
Microwave cavity made from YBaCuO

   W.J. Radcliffe, J.C. Gallop, C.D. Langham, M. Gee and M. Stewart

Summary: The authors report surface impedance measurements made on a cylindrical cavity resonator constructed entirely from the sintered high-temperature superconductor YBa/sub 2/Cu/sub 3/O/sub 7/. The temperature dependence of the surface impedance has been measured for five different modes in the frequency range 10-18 GHz and over the temperature range 4-300 K. Values for the penetration depth, linear coefficient of expansion, and normal state resistivity are derived from the data. The ultimate aim of this work is to produce very high Q cavities, operating far below their transition temperatures, where the temperature dependences of superconducting parameters become negligible. Such superconducting cavity resonators show promise as secondary frequency standards of the highest stability. The preliminary results with the first cavity are disappointing from this point of view.
Tunnel spectroscopy in Nb/BiSCCO point contact junctions

   A. Barone, A. Di Chiara, F. Fontana, G. Paterno, L. Maritato, G. Peluso, G. Pepe and U. Scotti di Uccio

Summary: Results concerning Nb/BiSCCO point contact junctions (PCJs) are presented. I-V (current voltage) and (dV/dI)-V measurements were performed at various temperatures and contact pressures. Differential resistance measurements performed by a standard modulation technique exhibits structures which can be related to the energy gap of BiSCCO. Features of the derivative plots are discussed in connection with models proposed previously for similar junctions. Nb-Nb PCJs based on sintered pellets of granular Nb have been investigated for comparison.
Microwave surface resistance of YBa/sub 2/Cu/sub 3/O/sub 7- delta /

   M. Kobayashi, K. Okabe, S. Tanuma, I. Sankawa, M. Sato, T. Konaka and K. Ishihara

Summary: The magnetic-field dependence of the microwave surface resistance of both single crystals and sintered crystals of YBa/sub 2/Cu/sub 3/O/sub 7- delta / (YBCO) has been measured at 24 GHz. The resistance decreases below the superconducting transition temperature and reaches a constant residual resistance. The value is much lower for single crystals than for polycrystals. Furthermore, polycrystals showed magnetoresistance at low field and magnetoresistance with hysteresis at high field, which resembles the magnetization behavior of typical type-II superconductors. The observed magnetoresistance is shown to be inherent to a sintered polycrystal which is composed of grains and contains many voids. The single crystal showed lower magnetoresistance.
Hot electron effect in the DC SQUID

   F.C. Wellstood, C. Urbina and J. Clarke

Summary: The authors investigated the temperature dependence of the noise in thin-film DC superconducting quantum interference devices (SQUIDS) down to 20 mK. The white noise measured in the early versions of the SQUIDS did not decrease as the bath temperature was lowered below 150 mK. The authors have attributed this saturation to a hot electron effect in the thin-film AuCu resistors shunting the Josephson junctions. A theoretical investigation showed that the temperature of the electrons in the shunts should be given by T/sub e/=(P/ Sigma Omega )/sup 1/5/, where P is the power dissipated in the shunts, Omega is the shunt volume, and Sigma is a proportionality constant. Experimentally, the authors found epsilon =(2.4+or-0.6)*10/sup 9/ WK/sup -5/ m/sup -3/. The shunts were redesigned, adding large thin-film cooling fins, to increase their volume substantially. This technique has reduced T/sub e/ to about 50 mK, with a corresponding improvement in the sensitivity of the SQUIDS.
Noise in DC SQUIDS with Nb/Al-oxide/Nb Josephson junctions

   M.W. Cromar, J.A. Beall, D. Go, K.A. Masarie, R.H. Ono and R.W. Simon

Summary: The authors have developed a process which incorporates very-high-quality Nb/Al-oxide/Nb Josephson junctions. The junctions had low subgap conductance, yielding V/sub m/ greater than 50 mV for critical current densities of 1000 A/cm/sup 2/. Low-inductance SQUIDS (superconducting quantum interference devices) made with these junctions were apparently free from junction conductance fluctuations, at least for frequencies above 1 Hz. A correlation between low leakage junctions and low noise from critical current fluctuations was observed. The SQUIDS exhibited flux noise with an unusual frequency dependence of currently unknown origin.
Low frequency noise in flux-locked DC SQUIDS

   Y. Miki, B. Muhlfelder, J.M. Lockhart and C.D. Tesche

Summary: The authors present the results of measurements of the noise of open-loop and flux-locked DC SQUIDs (superconducting quantum interference devices) at frequencies from 100 kHz to 10/sup -4/ Hz. The SQUIDs studied in this work were low-1/f-noise devices. Measurements were made in DC magnetic fields of 2*10/sup -3/ G using conventional shielding and also in an ultralow magnetic field environment of 10/sup -7/ G using expanded superconducting foil shields and a feedback-controlled slow cooling technique. The open-loop results are consistent with the earlier work of C.D. Tesche (1985). Some of the runs in the moderate-background-field environment (those with reduced shielding) showed a metastable structure in which switching between the metastable states was stimulated by electromagnetic interference. A description of the apparatus used for obtaining the various noise measurements is provided.
Investigation of noise sources in SQUID electronics

   T.R. Clem, M.J. Goldstein, J.W. Purpura, L.H. Allen, J.H. Claassen, D.U. Gubser and S.A. Wolf

Summary: The performance of SQUID (superconducting quantum interference device)-based electronics may be degraded from that found in laboratory operation. Investigations on superconducting tubes, wires, and sheets have been conducted to identify contributions to such noise. Results have been obtained for bulk and thin-film samples utilizing both the conventional low-temperature materials and the new high temperature oxide materials. Experiments have been conducted to quantify flux redistribution and flux motion in superconducting samples subjected to temperature changes, temperature gradients, and magnetic field gradients. These investigations have been conducted for magnetic fields typical of many SQUID applications, with field intensities much smaller than the critical values H/sub c1/. Penetration-depth, flux-pinning, and flux-motion effects have been observed. The various types of experiments conducted along with specific results are described.
Seven-channel RF SQUID with 1/f noises only at very low frequencies

   H. Ohta, M. Takahata, Y. Takahashi, K. Shinada, Y. Yamada, T. Hanasaka, Y. Uchikawa, M. Kotani, T. Matsui and B. Komiyama

Summary: A seven-channel RF SQUID (superconducting quantum interference device) with anodized short weak links has been fabricated. The devices exhibit a sensitivity of 23.6 fT/ square root Hz and a 1/f noise onset of 0.05 Hz at a white noise level of 1.8*10/sup -4/ phi /sub 0// square root Hz. The intrinsic flux noise is estimated from an observed step pattern to be 4.9*10/sup -5/ phi /sub 0// square root Hz. It is shown that Arnold theory explains very well the behavior of Josephson junctions with a critical current density of around 10/sup 4/ A/cm/sup 2/.
Low noise switching of a superconducting circuit by a laser induced weak link

   C.E. Cunningham, B. Cabrera, D.P. Saroff, J. Price and T. Stevenson

Summary: The authors have designed and begun testing a high-speed superconducting switch. The switches are lines of Nb about 400-A thick, 2- mu m wide, and 2-mm long on a sapphire substrate. The switching is done by illuminating the line with a laser through an optical fiber. The photons break Cooper pairs mostly by scattering, since the film thickness is on the order of the superconductor's coherence length and the optical penetration depth. The order parameter and critical current are depressed to zero through nonequilibrium dynamics, with the film remaining below its thermodynamic transition temperature. Thus, in principle, the switching rates are limited by the quasiparticle recombination time, rather than by the slower time of phonon escape from the film. The noise seen in the normal state is comparable to that in the superconducting state, and switching rates up to 300 kHz were used.
Reliable low noise DC-SQUID

   P. Carelli, V. Foglietti, R. Leoni and M. Pullano

Summary: A novel type of multiloop DC SQUID (superconducting quantum interference device) has been fabricated. The device is made of six different layers deposited on a 2-in silicon wafer; the layers are patterned by means of optical lithography. Every chip is a square 6.35 mm on a side and contains two SQUIDs and their input coils; the typical coil inductance is about 1 mu H. The junctions are 2 mu m/sup 2/ planar windows on SiO made of Nb-NbO/sub x/-PbAuIn with a current density of 500 A/cm/sup 2/ and V/sub m/ approximately=20 mV. The device was repeatedly cooled and stored in air for six months; after these thermal cycles no variations in critical current were observed. The measured mutual inductance between the input coil and SQUID is 2.1 nH, and the SQUID inductance is about 28 pH. The energy sensitivity referred to the input and in the flux-locked loop is approximately 1400 h in the white region with a 1/f corner frequency at 10 Hz. These SQUIDS are already operating in the gravitational wave experiment of the Rome group in Geneva.
A DC SQUID amplifier with a novel tuning circuit

   T. Takami, T. Noguchi and K. Hamanaka

Summary: The authors report a SQUID (superconducting quantum interference device) amplifier with a novel tuning circuit that can be easily coupled to a finite-impedance source. The SQUID amplifier is designed for a source impedance of 50 Omega and a signal frequency of nearly 150 MHz. The performance of the SQUID amplifier has been measured at 4.2 K. The measured gain and noise temperature of the SQUID amplifier are 20 dB and 0.7 K, respectively. A saturation temperature as high as 200 K at the input of the SQUID amplifier is achieved. It is concluded that this type of tuned SQUID amplifier is applicable to the IF (intermediate frequency) amplifier of the SIS (superconductor-insulator-semiconductor) receiver.
Measured performance parameters of gradiometers with digital output

   D. Drung, E. Crocoll, R. Herwig, M. Neuhaus and W. Jutzi

Summary: A planar first-order gradiometer and a DC SQUID (superconducting quantum interference device) comparator have been integrated on the same 6*6 mm/sup 2/ chip in Nb-Nb/sub 2/O/sub 5/-PbInAu technology and operated in a flux-locked loop. Owing to the digital gradiometer output, a very low flux noise of 7*10/sup -7/ phi /sub 0// square root Hz, a coupled noise energy of 34 times Planck's constant h, and a gradient noise of 3.8 pT/m square root Hz have been achieved in the white noise region above about 60 Hz. In spite of the very low flux noise, a maximum slew rate of 1.5*10/sup 5/ phi /sub 0//s at a signal frequency of 4 kHz has been measured. A simple modulation scheme has been developed to cancel Josephson junction critical-current fluctuations, yielding 4.5*10/sup -6/ phi /sub 0// square root Hz at 0.1 Hz.
Phase sensitive heterodyne receivers with SIS quasiparticle mixers

   M.F. Bocko, M.J. Wengler and Z.N. Zhang

Summary: It is noted that it is possible to operate a mixer as a phase-sensitive linear amplifier by pumping with two local oscillators (LOs) separated in frequency by twice the IF (intermediate frequency) and symmetrically located about the signal frequency. In principle a phase-sensitive amplifier can detect a signal without adding any noise. The authors present a formalism developed to describe two-LO mixers, and extend the quantum mixer theory to calculate expressions for the gain and noise of a two-LO mixer. The full quantum mechanical formulation used here enables an analysis of the mixer noise for general input states, for example, a squeezed state. It is demonstrated that a two-LO mixer is phase-sensitive. The results are pertinent to the design of phase-sensitive heterodyne receivers with SIS (superconductor-insulator-superconductor) quasiparticle mixers.
Numerical computation of two-LO SIS mixer gain and noise

   Z.N. Zhang, M.F. Bocko and M.J. Wengler

Summary: The authors present numerical calculations of the gain and noise of a two-LO (local oscillator) mixer based on an ideal SIS (superconductor-insulator-superconductor) IV curve. They demonstrate the phase-sensitive response of the mixer with two-LO pumping and present calculations of the noise for various DC bias conditions and embedding impedances. Preliminary results indicate that for certain DC bias conditions and signal terminations, the noise added to a signal by the two-LO mixer operated in the single-sideband mode can be a factor of 25 less than that added by a conventional single-sideband single-LO mixer.
Quasi-particle and pair current steps of Josephson junctions with radiation noise in a DC magnetic field

   W. Jutzi, E. Crocoll, D. Drung and G. Kramer

Summary: The current-voltage characteristics of a Josephson junction approximated by a long interferometer with many point junctions are simulated under the influence of a local oscillator at about half the gap frequency for different oscillator resistances. Without a DC magnetic field, pair current steps with hysteresis and quasi-particle steps appear in the same I-V characteristic. With appropriate magnetic fields, Shapiro steps can be reduced. However, even at the first and second zeros of the Josephson current, Shapiro steps of finite size are simulated. Modifications of current steps are described as a function of local oscillator noise. The simulated results are in qualitative agreement with measurements reported in the literature.
Numerical simulation of experimental data from planar SIS mixers with integrated tuning elements

   C.A. Mears, Q. Hu and P.L. Richards

Summary: The authors used the full Tucker theory including the quantum susceptance to fit data from planar lithographed millimeter-wave mixers with bow-tie antennas and integrated RF coupling elements. Essentially perfect fits to pumped I-V (current-voltage) curves have been obtained. The deduced imbedding admittances agree well with those dependently calculated from the geometry of the antenna and matching structures. It is found that the quantum susceptance is essential to the fit and thus to predictions of the mixer performance. For junctions with moderately sharp gap structures, the quantum susceptance is especially important in the production of steps with low and/or negative dynamic conductance.
NbN/MgO/NbN SIS tunnel junctions for submm wave mixers

   J.A. Stern, B.D. Hunt, H.G. LeDuc, A. Judas, W.R. McGrath, S.R. Cypher and S.K. Khanna

Summary: The authors report on the fabrication and testing of all-refractory NbN/MgO/NbN SIS (superconductor-insulator-superconductor) tunnel junctions for use as high-frequency mixers. Progress in the development of techniques for the fabrication of submicron-area tunnel junctions is described. Junction structures which have been investigated include mesa, crossline, and edge geometries. Using reactive sputtering techniques, NbN tunnel junctions with critical currents in excess of 10/sup 4/ A/cm/sup 2/ have been fabricated with V/sub m/ values as high as 65 mV and areas down to 0.1 mu m/sup 2/. Specific capacitance measurements on NbN/MgO/NbN mesa-type tunnel junctions give values in the range 60-90 fF/ mu m/sup 2/. These SIS tunnel junctions have been integrated with antennas and coupling structures for mixer tests in a waveguide receiver at 207 GHz. Preliminary mixer results are reported.
SNAP structures with Nb-AlO/sub x/-Nb junctions for MM-wave receivers

   A.B. Ermakov, V.P. Koshelets, I.L. Serpuchenko, L.V. Filippenko, S.V. Shitov and A.N. Vystavkin

Summary: High-quality small-area Nb-AlO/sub x/-Nb junctions have been fabricated by the selective niobium anodization process (SNAP). The influence of the preparation conditions on the junction properties were investigated. Numerical calculations based on I-V (current-voltage) characteristics measured by a data acquisition system were used to simulate the mixer performance. It has been shown that the knee-shaped structure on the I-V curve of refractory material junctions significantly affects the signal properties of the mixer. The signal and noise properties for different types of integrated SIS (superconductor-insulator-superconductor) mixing elements have been investigated experimentally in the frequency range of 37-53 GHz; the mixer conversion loss was as low as 4 dB at 45 GHz. The mixing elements consist of an odd number of SIS junctions connected in series for RF and in parallel for DC biasing. The DC bias wiring and IF (intermediate frequency) filters of these structures were designed to provide tuning out of junction capacitance and thin-film-electrode inductance.
Nb edge junction process for submillimeter wave SIS mixers

   W.C. Danchi, E.C. Sutton, P.A. Jaminet and R.H. Ono

Summary: The authors describe a junction fabrication process that produces high-quality Nb edge junctions of areas less than 0.2 mu m/sup 2/ on thin quartz (0.10 nm) substrates. This process utilizes a 10:1 projection wafer stepper for high-resolution and high-accuracy layer-to-layer registration. Large numbers of junctions were fabricated reliably with high-quality I-V (current-voltage) characteristics and with impedances suitable for use in SIS (superconductor-insulator-superconductor) mixers for submillimeter astronomy. Junctions produced by this process can be stored on the shelf for more than two years with no special precautions taken, and with an impedance change of less than 10%. No failures have been observed after thermal cycling. Currently these junctions are being used in an astronomical receiver that demonstrates state-of-the-art performance in the atmospheric window centered at 345 GHz. With some improvements to the process, it is possible to make junctions with areas sufficiently small for omega RC approximately=3 at 800 GHz.
All-NbN nanobridges as Josephson mixers

   T. Matsui, Z. Wang, K. Hamasaki, T. Yamashita and M. Endo

Summary: Using RIE (reactive in etching) and lift-off techniques, all-NbN nanobridges with gap structure in the I-V (current-voltage) curves have been reproducibly constructed for testing as millimeter-wave mixers. The nanobridges were constructed on NbN/MgO/NbN edge junctions. They were characterized by measurements of their I-V curve and dI/dV versus V and by mixing experiments at 105.9 GHz. These devices had high normal-state resistance, and showed almost ideal Josephson response to external magnetic flux and to millimeter-wave irradiation. The I-V curve remained nonhysteretic from T/sub c/ to 4.2 K, and millimeter-wave-induced steps in the I-V curve were observed up to approximately 3 mV. The cooling of the NbN nanobridges was quite good due to their small size and VTB geometry and the high thermal conductivity of the MgO films. Hence the Josephson response of these devices to millimeter waves was comparatively less limited by self-heating.
Harmonic mixing in a series array of short superconducting weak-links

   T. Matsui, B. Komiyama and H. Ohta

Summary: A new type of harmonic mixer using a series array of short superconducting weak-links is proposed for mixer applications at far-infrared and submillimeter-wave frequencies. The problem of limited mixer dynamic range can be eliminated by the use of a Josephson junction series array structure. Using a eleven-element series array, a preliminary experiment on harmonic mixing was carried out for two signals at 105.9 GHz and 5.4-12.6 GHz. IF (intermediate frequency) output was measured for each harmonic order from 9th to 19th by optimizing local power and bias voltage. In this experiment, 5-dB heightening of the signal-to-noise ratio was obtained at the IF output when the harmonic mixing order n was equal to the series element number, N=11.
Submillimeter wave generation using Josephson junction arrays

   K.-L. Wan, A.K. Jain and J.E. Lukens

Summary: A submillimeter-wave oscillator using a phase-locked array of Josephson junctions is demonstrated. With an array of 40 shunted tunnel junctions, the oscillator delivers 1 mu W of power at 350 GHz into a 60- Omega load on the chip. The operating frequency of the oscillator is tunable over a range of about 10%. Experiments on two coupled lead alloy tunnel junctions show that Josephson oscillations exist to about 1 THz. Using a similar design and a higher gap superconductor such as NbN for the transmission lines, arrays operating at 1 THz with power outputs of 1 mW should be feasible.
Microwave oscillator using arrays of long Josephson junctions

   S. Pagano, R. Monaco and G. Costabile

Summary: The authors report on measurements performed on integrated superconducting devices based on arrays of long Josephson tunnel junctions operating in the resonant fluxon oscillation regime (i.e. biased on the zero field steps). The electromagnetic coupling among the junctions causes a mutual phase-locking of the fluxon oscillations with a corresponding increase of the emitted power and a decrease of the signal linewidth. This phase-locked state can be controlled by means of an external DC bias current and magnetic field. The effect of the generated microwave signal has been observed on a small Josephson tunnel junction coupled to the array via a microstrip transmission line. The feasibility of the reported devices as local oscillators in an integrated microwave Josephson receiver is discussed.
Inductive coupling of a flux-flow type Josephson oscillator to a stripline

   K. Yoshida, J. Qin and K. Enpuku

Summary: A theoretical and experimental study of the coupling of the flux-flow-type Josephson oscillator (FFO) to an external stripline has been carried out to overcome the large impedance mismatch between them. For efficient coupling and impedance matching at millimeter and submillimeter wavelengths, the authors have proposed a scheme where the Josephson oscillator is inductively coupled to the stripline by a thin superconducting electrode. Theoretical modeling of the coupling section and the design of the stripline impedance-transformer have been carried out. In a preliminary experiment, the authors obtained a power of about 10/sup -7/ W emitted from the FFO into the stripline in the frequency range from 184 GHz to 193 GHz.
Noise driven fluctuations of Josephson junction series arrays

   P. Hadley, M.R. Beasley and K. Wiesenfeld

Summary: The shunted junction model is used to analyze the noise-driven fluctuations of series arrays of Josephson junctions. The total voltage across an array of coherently oscillating Josephson junctions is shown to exhibit two fundamentally different types of fluctuations, each of which makes its own characteristic type of contribution to the power spectrum. Phase fluctuations broaden the peaks in the power spectrum that correspond to the basic oscillations of the junctions and are primarily responsible for the linewidth of these oscillations. Transverse fluctuations contribute Lorentzian-shaped noise bumps to the power spectrum at the fundamental and harmonics of the basic Josephson oscillations. These noise bumps become larger and narrower at T/ beta /sub c/ increases, making a contribution to the linewidth for large beta /sub c/ and large bias currents. The form of these fluctuations is calculated in the limit of small noise, and it is shown that the fluctuations increase as a dynamical instability is approached.
Anomalous RF induced steps in resonant Josephson tunnel junctions for voltage standard maintenance

   U. Klein, J.H. Hinken, T. Gunther and D. Teklenburg

Summary: The authors theoretically investigated the current steps in the I-V (current-voltage) characteristics of a long Josephson tunnel junction driven by microwaves at frequencies near its geometrical resonance. They used a numerical algorithm based on a lossy transmission line model of the Josephson tunnel junction to calculate the DC current density distribution. In addition to the fundamental microwave frequency, harmonic contents of the tunneling current are also considered. The calculations show a strong asymmetric behavior of the current steps with respect to the quasi-particle curve. It is suggested that the excitation of higher harmonic waves gives rise to these anomalous microwave-induced steps. Due to the nonuniform DC-tunneling-current density distribution, the amplitudes of these current steps are not usually larger than 10% of the critical current. Since the critical current in long junctions is of the order of milliamperes, these amplitudes are considered relatively large.
Modulation of the penetration depth of Nb and NbN films by quasiparticle injection

   E.K. Track, M. Radparvar and S.M. Faris

Summary: A novel approach to modulating the inductance of a superconducting microstrip is described. This approach could be the basis for numerous practical applications, such as phase-shifters and high-frequency tuning elements. The physical mechanisms involved are quasiparticle injection, gap suppression, and penetration-depth modulation. The authors have investigated the modulation of the penetration depth of niobium and niobium nitride films by excess quasiparticle injection. To this effect, all niobium and all-niobium-nitride SQUID (superconducting quantum interference device) circuits were designed and fabricated. These circuits allow quasiparticle injection into the inductive element of the SQUID. This injection is achieved by optical irradiation through an opening in a Nb reflective layer which partially masks the rest of the circuit or electronic current injection through a tunnel junction overlaid on the microstrip inductance. Penetration-depth modulation is achieved with both methods. The magnitude of the effect varies from 10% to over 200% change in inductance.
Design of variable phase velocity kinetic inductance delay lines and their measured characteristics when fabricated by a simple Nb based process

   G.K.G. Hohenwarter, J.S. Martens, J.B. Beyer, J.E. Nordman and D.P. McGinnis

Summary: A simple design for superconducting kinetic inductance delay lines is presented. Delay lines were fabricated with a thin-film process involving only DC magnetron deposition and anodization of Nb. Phase-velocity measurements demonstrated wave slowing to less than 1/150 of the velocity of light in free space with associated impedances in the ohm range. Phase velocity changes on lines which were in physical proximity to long Josephson junctions and normal conducting lines were investigated. Variations larger than 10% of the equilibrium value were observed with junction-coupled lines under bias application. Locally heated lines exhibited changes exceeding a factor of two. Loss and phase velocity were determined as a function of bias conditions in both cases. Measured line loss was within expectations.
Superconducting stripline resonator performance

   B.R. McAvoy, G.R. Wagner, J.D. Adam, J. Talvacchio and M. Driscoll

Summary: Reliable techniques for evaluating the microwave properties of superconductors are essential in providing calibrated data for exchange between laboratories and for developing practical device designs. The authors are examining the techniques which utilize microwave stripline resonators. These resonators provide for the rapid measurement of microwave parameters in a repeatable fashion with minimal constraints on processing. Sandwiched microstrip line resonators are used to compare the performance at 4.2 K of OFHC copper and superconducting films of Pb, Nb, and YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) at C-band and X-band. Typical results for the Nb resonators show a loaded Q/sub L/ of about 8*10/sup 4/ with a transmission insertion loss of 5 dB at 3 GHz. Initial results on a YBCO a-axis film used as a ground plane in the Nb resonator yield a surface resistance value of about 10/sup -3/ Omega at 2.8 GHz. Preliminary results on the phase noise performance of a Nb resonator at 2.9 GHz are presented.
Thermal study of semiconductor-superconductor hybrids

   E. Raicu and T. Van Duzer

Summary: The authors have conducted an experiment to evaluate the thermal problems that would result if a GaAs amplifier chip were flip mounted via solder-ball connections to an otherwise superconducting receiver on a larger Si chip. The GaAs chip is modeled by a chip carrying a thin-film resistor, which is used to dissipate the same amount of heat as the GaAs IF (intermediate frequency) amplifier. The energy gaps exhibited by Nb tunnel junctions are used to monitor the temperature in a number of places surrounding the heat source. The results indicate that thermal effects do not preclude the use of semiconductor-superconductor hybrid receivers. The data indicate that for applications involving power dissipation less than 150 mW (gain of up to 45 dB) on a chip of area of approximately 0.1 cm/sup 2/, neither switching of lines nor thermal fluctuations of devices is likely to be a problem when the devices are at least 1 mm from the edge of the chip and away from the path of the helium bubbles. The limit on power dissipation is likely to be temperature fluctuations rather than excessive temperature.
Inductance calculation system for superconducting circuits

   M. Hosoya, E. Goto, N. Shimizu, N. Miyamoto and Y. Harada

Summary: A method for calculating the inductance of complicated three-dimensional superconducting circuits is described. The current distribution is obtained by assuming that the edge currents satisfy both Maxwell's and London's equations. Inductance is calculated from the magnetic energy resulting from the current. Extrapolations are used to reduce the computational requirements and to increase the accuracy of the results. Using the method, a CAD (computer-aided design) system was developed for superconducting circuits. The inductance of 3-D superconducting circuits, which was unattainable except by experiments, can be easily calculated by this system. The coupling inductance of a DC SQUID (superconducting quantum interference device) is calculated using the CAD system. Agreement between experiment and the computation is good.
Dielectric constant of evaporated SiO at frequencies between 13 and 103 GHz

   H.K. Olsson

Summary: An integrated Josephson tunnel junction and microstrip resonator have been used to determine the dielectric constant of evaporated SiO. The method is straightforward in that it uses conventional microwave techniques to calculate the impedances for different frequencies and parasitic effects are negligible. A frequency-independent value of 5.5+or-0.4 was calculated for the 13- to 103-GHz range. At each resonant frequency a step appeared at the corresponding voltage in the current-voltage curve. For each resonant frequency, a dielectric constant was calculated. The constant does not change appreciably from the average value of 5.5 throughout the whole frequency range, in agreement with previous measurements.
Effects of intrinsic stress on submicrometer Nb/AlO/sub x//Nb Josephson junctions

   T. Imamura and S. Hasuo

Summary: The intrinsic stress and its relaxation process are discussed for sputtered Nb films used for the electrodes in Nb/AlO/sub x//Nb Josephson junctions. The stress, optically measured for Nb films, depends on the Ar pressure during sputtering, and it changes from compressive to tensile when the Ar pressure is increased. From X-ray diffraction, the shift in the lattice constant was observed to be proportional to the film stress. Changes in the lattice constant were also clearly observed when Nb films were etched to fine patterns. This suggests that the intrinsic stress in Nb films is relaxed at peripheral areas after the patterning process, and that such relaxation is one cause of deterioration in current-voltage characteristics frequently observed in small Josephson junctions. This indicates that stress-free Nb should be used for submicrometer junctions.
A new self-aligning process for whole-wafer tunnel junction fabrication

   M.G. Blamire, J.E. Evetts and D.G. Hasko

Summary: The authors have developed a processing method for whole-wafer tunnel junctions which allows the preparation of planar tunnel junctions with just two lithographic steps and largely eliminates the inherent capacitance and potential failure problems associated with overlap between the base electrode and the counterelectrode metallization common to all existing methods. The basic feature of this self-aligning whole-wafer (SAWW) process is that the pattern used to create the counterelectrode metallization also defines the junction area. Results of preliminary trials of this method are presented and possible future developments discussed.
Processing techniques for refractory integrated circuits (superconducting)

   J.X. Przybysz, R.D. Blaugher and J. Buttyan

Summary: Processing techniques have been developed to increase yields and uniformity in superconductor integrated circuits fabricated with refractory materials. An eight-level process was used to define a ground plane, ground plane insulator, Josephson junction base and counterelectrodes, a second insulator layer, superconductor interconnections, resistors, and gold contact pads. Every layer, except the gold, was patterned by reactive ion etching (RIE). A resistor structure was developed that included an etch stop layer. The formation of polymers, which occurs with etch gases containing carbon, was inhibited by the addition of oxygen to the plasma. RIE of insulator vias was accomplished with a mixture of NF/sub 3/ and Ar that gave good selectivity for silicon dioxide over niobium. Stress-free films of niobium, molybdenum, and silicon dioxide were obtained by adjusting the sputtering gas pressure. Molybdenum resistors, deposited as a top layer, were trimmed by RIE as a post-testing step to improve circuit performance.
Characterization of Nb/AlO/sub x/-Al/Nb junction structures by anodization spectroscopy

   T. Imamura and S. Hasuo

Summary: The thin tunneling barrier in a Nb/AlO/sub x/-Al/Nb Josephson junction was characterized by anodization spectroscopy. Nb/AlO/sub x/ and Al/Nb interfaces made by varying certain process parameters were examined. The interface quality is greatly affected by film thickness, layer sequence, annealing, and existence of a thin oxide. It is concluded that anodization spectroscopy is a useful technique to diagnose the tunneling barrier in the Nb/AlO/sub x/-Al/Nb Josephson junctions during fabrication processes.
Characteristics of vertically-stacked planar tunnel junction structures

   M.G. Blamire, R.E. Somekh, G.W. Morris and J.E. Evetts

Summary: Whole-wafer multilayer tunnel structures consisting of vertically stacked Al/sub 2/O/sub 3/ tunnel barriers separated by thin Nb layers have been deposited under UHV (ultrahigh vacuum) conditions, with repeat distances ranging from 10-50 nm. Using a modification of the conventional SNEP process, these structures have been fabricated into vertical series arrays. Using this technique it is possible to select different numbers of junctions on the same substrate and so determine the properties of each barrier. Information gained from such structures provides a considerable insight into the factors determining junction characteristics such as critical current density and quality as well as serving as the basis for the study of novel types of structures and devices.
Niobium trilayer process for superconducting circuits

   J.M. Murduck, J. Porter, W. Dozier, R. Sandell, J. Burch, J. Bulman, C. Dang, L. Lee, H. Chan, R.W. Simon and A.H. Silver

Summary: A Nb-AlO/sub x/-Nb trilayer process was developed that consistently produces junctions with V/sub m/>40 mV. Critical current density was controlled reproducibly from 200 to 7000 A/cm/sup 2/ by controlling the oxygen pressure in the process chamber during thermal oxidation of the aluminum. A multilayer AlO/sub x/ barrier was used to produce junctions for Josephson circuit applications requiring low critical currents (<50 A/cm/sup 2/). A second Al deposition and oxidation was able to reproducibly control the critical current density from 6 to 200 A/cm/sup 2/. High quality (V/sub m/>40 mV) Josephson junctions have been fabricated with low stress (<1 Gdyne/cm/sup 2/) by an appropriate choice of niobium deposition rate (8 to 9 AA/s) and argon sputtering pressure (4 mtorr).
Low-loss lumped-element capacitors for superconductive integrated circuits

   M. Bhushan, J.B. Green and A.C. Anderson

Summary: Low-loss lumped-element capacitors for superconductive circuits were fabricated using sputter-deposited Nb electrodes. The dielectric layer was formed by partially anodizing the Nb base electrode. The deposition technique for the counterelectrode strongly affected the parasitic shunt conductance of the capacitors. It was found that this conductance could be reduced by depositing the Nb counterelectrode films by DC magnetron sputtering at a low rate and at a high Ar pressure. By optimizing these process parameters, capacitors with breakdown voltages greater than 85% of the anodic oxide formation voltage and loss tangents less than 0.003 at 10 MHz were fabricated. These capacitors were integrated with Nb thin-film inductors to produce L-C resonators with quality factors greater than 400.
A DC SQUID with intrinsically shunted submicron junctions near the hysteretic limit exhibiting an extremely large dV/d phi transfer function

   E.P. Houwman, R. Cantor, M. Peters, H.J. Scheer and H. Koch

Summary: A fabrication process yielding submicron-scale Josephson junctions has been developed. The junction consists of two metal striplines lying in line and separated by a vertical barrier. Thus the contact area is determined by the width and thickness of the striplines. The capacitive coupling is only due to the small contact area, because there is no layer overlap. The process was applied to all-Nb thin-film junction technology with nitrided Si barriers. The I-V (current-voltage) curves of these junctions show the characteristic features of superconductor-normal-superconductor contacts. DC SQUIDs (superconducting quantum interference devices) made of these junctions exhibit characteristics competitive with those of high-quality tunnel-junction DC SQUIDs.
Simple DC-SQUID system based on a frequency modulated relaxation oscillator

   M. Muck and C. Heiden

Summary: Nanobridges with hysteretic I-V (current-voltage) characteristics can be operated as relaxation oscillators when connected to an R-L shunt. A DC SQUID (superconducting quantum interference device) configuration results if two such oscillators are incorporated in a superconducting ring. Operating such a self-oscillating SQUID (SOS) with a suitable bias current leads to an output signal of the order of 10 mV, whose frequency depends on the magnetic flux through the SQUID ring modulo Phi /sub 0/. Due to this large output voltage, no impedance matching or special low-noise preamplifier is needed for the readout scheme. Standard integrated circuits for FM (frequency modulated) signal processing can be used, leading to matchbox-size electronics. Such DC SQUIDs have been made of thin Nb, NbN, and Nb/sub 3/Ge films. The highest sensitivity achieved so far is Nb devices with a white flux noise below 10/sup -5/ Phi /sub 0// square root Hz at 4.2 K.
Low noise operation of a DC SQUID in a large beta regime and its application to the design of a high T/sub c/ SQUID

   K. Enpuku, S. Kohjiro and K. Yoshida

Summary: The noise characteristics of a large- beta DC SQUID (superconducting quantum interference device) have been studied experimentally in the case where the SQUID inductance is resistively shunted. Energy resolutions of the SQUIDs, epsilon , have been measured for various beta values up to beta =19. It is shown experimentally that the energy resolution of these large- beta SQUIDs is as small as that of the conventional SQUID with beta =1. For example, an energy resolution of 25h was obtained for beta =12 (L= 340 pH and I/sub 0/=37 mu A), where h is Planck's constant. The experimental results agree quantitatively with theoretical ones. It is also shown that the present resistivity shunted inductance scheme is very useful in developing SQUIDs operating at T=77 K with high-T/sub c/ superconductors, where the value of beta will necessarily be large in order to avoid noise effects. Numerical simulations of the performance of the high-T/sub c/ SQUID are presented.
Current amplifier and flux-buffer designs using an exponential flux shuttle with a Josephson junction synthetic inductor

   M. Gershenson

Summary: A current amplifier design based on the principle of fluxon propagation in a multijunction exponential flux shuttle has been investigated. In this design, the critical current of the junctions is increased exponentially and the SQUID (superconducting quantum interference device) inductance is a Josephson-junction equivalent inductance. Current gain can be achieved by generating fluxons at the low end and dissipating them at the high end where the load is located. Advantages over other types of linear devices are discussed. Two parallel exponential flux shuttles can be used to duplicate flux from a high-inductance input coil to a low-inductance output. The device performance of the two circuits is evaluated by computer simulation, and noise performance is discussed.
DC-SQUID magnetometer system for detecting vector value of magnetic field

   M. Nakanishi, N. Kasai, H. Kado and M. Koyanagi

Summary: A vector magnetometer system for biomagnetic applications is described. The system consists of two vector magnetometers, each comprising three integrated SQUID (superconducting quantum interference device) magnetometers located perpendicularly to each other to detect three orthogonal components of the magnetic field simultaneously. The resolution of each orthogonal component is 11 fT/ square root Hz in the write noise region. This system has been used in magneto-cardiography and for measuring the spontaneous magnetic field from the human brain.
An integrated DC SQUID gradiometer for biomagnetic application

   M. Koyanagi, N. Kasai, K. Chinone, M. Nakanishi, S. Kosaka, M. Higuchi and H. Kado

Summary: A first-order off-diagonal gradiometer was fabricated and tested. The gradiometer consisted of two field pickup coils and a planar DC SQUID (superconducting quantum interference device) with two superconducting loops connected in parallel, two multiturn input coils, and a modulation-feedback coil. The size of the pickup coils was 6*6 mm/sup 2/ with a base line of 8 mm. The overall size of the gradiometer was 15*7.5 mm/sup 2/. The resolution of the magnetic field gradient of the gradiometer increased from 11 to 1.8 pT/m square root Hz (the noise limits), corresponding to the frequencies from 1 Hz to 600 Hz. The resolution became nearly white in a frequency range above 600 Hz. The intrinsic balance of the gradiometer was better than 1000 p.p.m. for the field perpendicular to its plane.
Experimental localization ability of planar gradiometer systems for biomagnetic measurements

   A.C. Bruno, V. Pizzella, G. Torrioli and G.L. Romani

Summary: The localization ability of SQUID (superconducting quantum interference device) planar gradiometers for biomagnetic applications has been investigated. A linear planar superconducting-wire gradiometer was constructed and tested. Localization tests were performed both on a current dipole model and on human subjects. It is shown that the accuracy of localization results was not significantly affected by the use of the planar configuration.
Thermal activation and macroscopic quantum tunneling in a DC SQUID

   F. Sharifi, J.L. Gavilano and D.J. Van Harlingen

Summary: The authors report measurements of the transition rate from zero-voltage metastable minima in the two-dimensional potential of a DC SQUID (superconducting quantum interference device) as a function of applied flux and temperature. A crossover is observed from thermally activated escape to macroscopic quantum tunneling at a critical temperature that is a strong function of the bias flux. The macroscopic quantum tunneling rate is substantially reduced by damping, which also broadens the crossover region. The authors unexpectedly observed thermal rates that are significantly suppressed from those predicted by the classical two-dimensional thermal activation model, as if the potential barrier for activation were effectively enhanced. They discuss possible explanations for this result, based on the interaction of the macroscopic degrees of freedom in the device and energy level quantization effects.
Relaxation-oscillation-driven DC SQUIDs

   S.A. Gudoshnikov, Y.V. Maslennikov, V.K. Semenov, O.V. Snigirev and A.V. Vasiliev

Summary: Simple and reliable relaxation-oscillation (RO)-driven DC SQUIDs (superconducting quantum interference devices) have been fabricated with a flux-to-voltage factor H up to 1 mV/ Phi /sub 0/ and internal energy sensitivity E/sub v/ of (4+or-1) * 10/sup -31/ J/Hz at frequencies above 10 Hz and 1*10/sup -29/ (1 Hz/f) J/Hz at lower frequencies. Supplied with a 50- mu m-wire 20-turn spiral input coil and a 6-cm/sup 2/ pickup loop, such SQUIDs provided magnetic field sensitivity close to (6+or-3)*10/sup -15/ T/Hz/sup 1/2/ above 10 Hz. The dynamic range of the magnetometers was close to 1.5*10/sup 7/ Hz/sup 1/2/ above 10 Hz. The maximum slew rate was about 10 mu T/s at 0.1 kHz. Successful records of Earth-ionosphere magnetic resonances have been obtained with these magnetometers housed in a stainless steel transport dewar. A balanced version of the RO-driven DC SQUID is suggested with improved H and E/sub v/.
DC SQUID preamplifier for DC-SQUID magnetometer

   V.P. Koshelets, A.N. Matlashov, I.L. Serpuchenko, L.V. Filippenko and Y.E. Zhuravlev

Summary: A DC SQUID (superconducting quantum interference device) magnetometer with DC SQUID preamplifier has been designed and experimentally tested. The total magnetometer noise was reduced to the intrinsic noise level of the input DC SQUID, and magnetometer cryogenic containment was minimized by using the DC SQUID preamplifier. Two identical thin-film DC SQUIDs with 15- mu m/sup 2/-area resistively shunted Nb-AlO/sub x/-Nb junctions were utilized. The resulting magnetometer had a coupled energy sensitivity equivalent to 3*10/sup -31/ J/Hz in the range from 1 Hz to 30 kHz and about 100-dB dynamic range.
Picosecond magnetic spectroscopy with integrated DC SQUIDs

   D.D. Awschalom and J. Warnock

Summary: Advanced VLSI (very large scale integration) technology was used to fabricate ultraminiature integrated SQUID (superconducting quantum interference device) susceptometers. With the appropriate design parameters, the sensitivity of the devices approaches the quantum limit. The use of integrated circuits in conjunction with pulsed optical techniques allows magnetic systems to be probed with a picosecond time resolution. The response can be mapped out as a function of the energy of the optical excitation, providing detailed spectroscopic information. Applying these techniques to the study of II-VI dilute magnetic semiconductors has yielded new insight into the mechanics of magnetic polaron formation and the dynamics of the magnetic spins. First experiments were carried out on a small approximately 10*10*1- mu m/sup 3/ single crystal platelet of Cd/sub 0.8/Mn/sub 0.2/Te. The results of the time-averaged magnetic spectroscopy at two different temperatures are presented, displaying the magnetic response to optical excitation at constant intensity from a photon energy of 1.83 to 2.0 eV.
Nuclear magnetic resonance with DC SQUID preamplifiers

   N.Q. Fan, M.B. Heaney, J. Clarke, D. Newitt, L.L. Wald, E.L. Hahn, A. Bielecki and A. Pines

Summary: Describes five experiments illustrating the application of DC SQUID (superconducting quantum interference device) amplifiers to magnetic resonance experiments. The first experiment involved the observation of nuclear spin noise, that is the spontaneous emission of photons from an ensemble of /sup 35/Cl nuclei in the zero polarization state. The second experiment involved the use of the Q-spoiler in conventional NQR (nuclear quadrupole resonance) and NMR measurements in which one applies a large RF pulse to the nuclei to make them precess. The Q-spoiler was then used in an experiment to detect the oscillating electric polarization induced by /sup 35/Cl nuclear quadrupole moments. The fourth experiment involved the extension of the use of the Q-spoiler and SQUID amplifier to NMR, detecting the signal from /sup 119/Sn nuclei at 30 MHz. Finally, a SQUID amplifier was used with an untuned input circuit to detect the low-frequency NMR signal at 55 kHz from /sup 195/Pt nuclei in an applied field of 60 Gauss.
A comparison of the performance of planar and conventional second-order gradiometers coupled to a SQUID for the NDT of steel plates

   S. Evanson, R.J.P. Bain, G.B. Donaldson, G. Stirling and G. Hayward

Summary: The authors have developed a DC magnetic NDT (nondestructive testing) technique using a SQUID (superconducting quantum interference device) coupled to a planar gradiometer for the inspection of structures such as flat steel plates and steel pipes. Design criteria for the gradiometer are presented and used to demonstrate the superior performance of the planar approach compared to that of a second-order axial gradiometer of conventional design. The authors show an example of the use of system for mapping the magnetic field above a steel plate containing ideal defects. The proposed SQUID system is shown to operate normally in an unscreened laboratory close to a steel specimen in the presence of a DC magnetizing field in excess of 20 mT.
Use of a superconductive gradiometer in an ultrasensitive electromagnetic metal detector

   P.V. Czipott and W.N. Podney

Summary: The authors present an electromagnetic gradiometer that uses a SQUID (superconductor quantum interference device) sensor as the receiver in an active, electromagnetic detector of nonferrous as well as ferrous objects. The gradiometer pickup loops sit in the center of magnetic coils that generate a time-varying magnetic field inducing eddy currents in conductive bodies. The gradiometer measures the secondary magnetic field of the eddy currents. The SQUID's sensitivity at frequencies below 1 kHz makes electromagnetic metal detectors practical in the marine environment, where the electrical conductivity of seawater precludes the use of conventional systems. The authors describe a prototype system that attains a detection range of 10 m in seawater for targets 50 cm in diameter. It operates at frequencies from 1 Hz to a few hundred Hz. Uses of the electromagnetic gradiometer include locating naval mines buried in sea bottom sediments and hunting undersea treasure. The system's response to the seawater itself enables application to airborne electromagnetic bathymetry. Over land, its sensitivity to crustal conductivity contrasts makes it suitable for airborne mineral exploration.
Status of Stanford magnetic monopole search with eight-loop superconducting detector

   M.E. Huber, B. Cabrera, M.A. Taber and R.D. Gardner

Summary: A model has been developed which includes all significant inductive coupling of the Stanford monopole detector pickup loops and allows variation of the individual inductances to optimize the fit to the data. With this model, one can calculate the response of the detector to monopoles, with allowances for the inoperative panels and discrepancies in the inductances. The detector has been in operation for approximately 450 days at this time. Of this, there are 6600 hours of computer data, and 6000 of these hours meet the criteria for active sensing time. No candidate monopole events have been observed. The exposure to date represents a limit on the flux of cosmic ray magnetic poles of 7.8*10/sup -13/ cm/sup -2/ s/sup -1/ sr/sup -1/ at 90% confidence level.
Design, fabrication, and performance of integrated miniature SQUID susceptometers

   M.B. Ketchen, D.D. Awschalom, W.J. Gallagher, A.W. Kleinsasser, R.L. Sandstrom, J.R. Rozen and B. Bumble

Summary: The design, construction, and performance of miniature SQUID (superconducting quantum interference device) susceptometers is discussed. Spins (in units of mu /sub beta /) per square root Hz has been identified as an important figure of merit. Simple expressions for S/sub n/ (spin sensitivity) in miniature SQUID susceptometers are developed and the implications of dimensional scaling explored. The details of several existing and proposed designs are reviewed, including versions that utilize commercial SQUIDs. With thin-film DC SQUIDs, S/sub n/ values of a few thousand spins/ square root Hz have already been obtained, and it is projected that values of a few hundred will be achieved soon.
SQUID detection of electronic circuits

   R.L. Fagaly

Summary: The author reports on the use of a SQUID (superconducting quantum interference device) magnetometer to detect audio-frequency timing signals from electronic and electromechanical clock circuits. Narrowband spectrum analysis was used to determine the quality factor (Q) in one case. Magnetic field maps indicated that the source of the magnetic fields could be localized to better than 1 mm. X-rays showed the presence of circuit elements in the region of the magnetic field maxima. Interpretation of the field sources as magnetic dipoles yielded m/sub 2/ values ranging from 10/sup -6/ Am/sup 2/ to 10/sup -8/ Am/sup 2/. The implication of this work is that SQUID magnetometers have potential use in noncontact detection of timing signals of timing circuits and microprocessors.
Spatial deconvolution algorithm for superconducting planar gradiometer arrays

   A.C. Bruno and P.C. Ribeiro

Summary: A digital filter model used previously to describe axial gradiometers is used to study arrays of planar first-order gradiometers. As an application of this technique, a spatial deconvolution algorithm is developed to recover the input field from the output measurements. The influence of parameters such as source depth and the gradiometer array density is investigated by means of computer simulations. With properly designed array the input flux was recovered with errors between 3% and 12%. This provided a contour plot quite similar to the one that would be obtained if the source were detected with a single-loop coil array.
Submicron NbN Josephson tunnel junctions for digital applications

   M. Aoyagi, A. Shoji, S. Kosaka, H. Nakagawa and S. Takada

Summary: Submicron NbN/MgO/NbN Josephson tunnel junctions for Josephson integrated circuits were investigated. The junctions have been fabricated by the cross-line patterning (CLIP) method with an electron-beam (EB) direct-writing technique. The all-refractory fabrication process for logic circuits using the CLIP method is presented. This process is applied to the fabrication of a logic gate of 4JL containing 0.8- mu m-square junctions as an example of digital application. A logic gate has been fabricated by this process, and its characteristics are discussed.
RF-sputter-deposited magnesium oxide films as high-quality adjustable tunnel barriers

   J.C. Villegier, M. Radparvar, L.S. Yu and S.M. Faris

Summary: High-quality RF-sputtered MgO films as tunnel barriers to fabricate small-area nitride tunnel junctions. A magnetism oxide barrier deposited as a single layer or as a multilayer film results in devices with similar characteristics. Annealing trilayers at temperatures in excess of 250 degrees C for several hours decreases junction current density and improves device quality, presumably by increasing barrier heights through reducing resonant tunneling states. A self-aligned process utilizing only two mask levels is used to produce junctions as small as 0.5 mu m/sup 2/ with excellent critical current uniformity. These junctions exhibit energy gaps of 5.1 mV and low subgap currents at current densities in excess of 1000 A/cm/sup 2/, which make them suitable for a variety of applications such as SIS (superconductor-insulator-superconductor) mixers and logic circuits.
Properties of stacked NbN tunnel junctions

   H. Hedbabny and H. Rogalla

Summary: Stacks of up to three tunnel junctions were fabricated using the NbN-MgO technique. Different preparation methods were tested, and two gave favorable results. In the first one, the whole stack is prepared in situ and structured afterwards by lift-off and reactive and argon ion etching. The authors investigated the resulting I-V (current-voltage) characteristics of stacks of 8.3 mV. Since it was not possible to establish electrical connections to the intermediate electrodes by this method, a second one was applied in which each NbN/MgO layer is prepared in a separate step and structured by lift-off. Here the I-V characteristics, the interaction between the tunnel junctions, and their RF properties were investigated. Shapiro steps and photon-assisted tunneling were observed in the I-V characteristics of a receiver junction, while the bottom tunnel junctions were used as microwave generators.
NbN based Josephson junctions with silicon barriers deposited at 700/spl deg/C

   E.J. Cukauskas and W.J. Carter

Summary: The authors have fabricated NbN/Si/Nb tunnel junctions where the barriers were deposited at substrate temperatures to 700 degrees C. The device characteristics for those tunnel junctions with V/sub m/ (figure of merit) values exceeding 15 mV were studied as a function of the barrier deposition temperature. A reduced NbN energy gap was observed for barriers deposited at high substrate temperatures, possibly due to an interaction of the silicon with the NbN or an off-stoichiometric surface resulting from the high temperature sputter etch of the base electrode. The zero-bias conductivity as a function of temperature was measured for thick barriers and found to follow an activated conduction process at the high temperatures and Mott hopping conduction at the lower temperature. Some initial measurements on germanium barriers deposited at 250 degrees C were made and found to follow a similar behavior except at a much lower temperature, possibly due to a lower activation energy.
NbN edge junction fabrication: edge profile control by reactive ion etching

   X.F. Meng, R.S. Amos, A.W. Lichtenberger, R.J. Mattauch and M.J. Feldman

Summary: In order to fabricate NbN edge junctions with low parasitic capacitance, an insulator with low dielectric constant, such as SiO/sub 2/, must isolate the base and counterelectrode except on the edge. Reactive ion etching was used to cut an edge in SiO/sub 2//NbN bilayer films. For this process it is necessary that SiO/sub 2/ be etched more rapidly than NbN to form a suitably sloped edged profile. The authors investigated the influence of etching gas composition and other parameters on etching rates and edge profiles, using CF/sub 4/, CF/sub 4//O/sub 2/, CF/sub 4//CH/sub 4/, CF/sub 4//CHF/sub 3/, and CHF/sub 3/. It was found that CF/sub 4/ and CF/sub 4//O/sub 2/ plasma etching generally yields poor, undercut edge profiles. However, satisfactory edge profiles were obtained with the other three gas combinations. The edge angle can be controlled by changing the proportions of the gases. Using this process, the authors have successfully fabricated NbN/oxide/PbBi edge junctions with <1 mu m/sup 2-/ area by standard optical photolithography.
The effects of ion gun beam voltage on the electrical characteristics of NbCN/PbBi edge junctions

   A.W. Lichtenberger, M.J. Feldman, R.J. Mattauch and E.J. Cukauskas

Summary: The authors have succeeded in fabricating high-quality submicron NbCN edge junctions using a technique which is commonly used to make Nb edge junctions. A modified commercial ion gun was used to cut an edge in SiO/sub 2//NbCN films partially covered with photoresist. An insulating barrier was then formed on the exposed edge by reactive ion beam oxidation, and a counterelectrode of PbBi was deposited. The electrical quality of the resulting junctions was found to be strongly influenced by the ion beam acceleration voltages used to cut the edge and to oxidize it. For low ion beam voltages, the junction quality parameter was as high as V/sub m/=55 mV (measured at 3 mV), but higher ion beam voltages yielded strikingly poorer quality junctions. In light of the small coherence length of NbN ( xi approximately=3 nm), the dependence of the electrical characteristics on ion beam voltage is presumably due to mechanical damage of the NbCN surface. In contrast, for similar ion beam voltages, no such dependence was found for Nb( xi approximately=30 nm) edge junctions.
Fabrication of Nb/Al-Al/sub 2/O/sub 3//Nb junctions with extremely low leakage currents

   A.W. Lichtenberger, C.P. McClay, R.J. Mattauch, M.J. Feldman, S. Pan and A.R. Kerr

Summary: Nb/Al-Al/sub 2/O/sub 3//Nb trilayer films were deposited using DC magnetron sputtering guns in a UHV (ultrahigh vacuum) system which is capable of 5*10/sup -10/ Torr. SIS (superconductor-insulator-superconductor) junctions as small as 3.2*3.2 mu m/sup 2/ were isolated from the trilayer by standard photolithography. The junctions typically have V/sub m/=70-90 mV at 4.2 K, while at 2.0 K, V/sub m/ is as large as 1 V. This corresponds to a subgap current of 0.15% of the quasiparticle current rise. The subgap leakage current is compared to the predictions of the BCS (Bardeen-Cooper-Schrieffer) theory. The specific capacitance is preliminarily measured to be 45+or-5 fF/ mu m/sup 2/.
Supercurrent nonuniformities by ion implantation in niobium based Josephson junctions

   C. Camerlingo, B. Ruggiero, M. Russo and E. Sarnelli

Summary: Nitrogen ion implantation was used to induce local modifications of the superconductive properties of the niobium base layer in Nb-NbO/sub x/-Pb Josephson tunnel junctions. A local depression of the niobium critical temperature and energy gap turns into a nonuniform critical current density profile J/sub c/ in the sample. Different profiles have been obtained by modifying the implanted region geometry and the nitrogen ion concentration. The external magnetic field dependence of the maximum DC Josephson current has been used as a diagnostic tool to obtain a preliminary characterization of the shape of J/sub c/ in a small sample. Preliminary investigations on long junctions are also reported.
Processing of thick-film dielectrics compatible with thin-film superconductors for analog signal processing devices

   S.C. Wong, A.C. Anderson and D.A. Rudman

Summary: The authors demonstrate the feasibility of integrating thick-film dielectrics with thin-film superconductors in the fabrication of signal processing devices. Thin films of Nb and NbN are deposited by RF sputtering and patterned photolithographically. Thick film dielectrics can be spun on to a controlled thickness of 10 to 25 mu m, which is an optimum range for high-density, low-loss microwave delay lines. After an organic-binder burnout step at 450 degrees C in air, the ceramic dielectrics are sintered onto the NbN thin films at 850 degrees C in vacuum. The transition temperature of the NbN changes from 15 K as sputtered to 9 K after sintering, but superconductivity is preserved by the presence of thin-film MgO and SiO/sub 2/ barrier layers. Lumped-element resonators, in which the inductor and the capacitor electrodes are made of NbN and the dielectric of thick-film ceramic, have been successfully fabricated for measuring the dielectric properties of the ceramics at 4.2 K and 10 MHz. Preliminary results indicate a dielectric constant of 6-8 and tan delta of 10/sup -2/.
Experimental results of a vortex flow transistor amplifier

   D.P. McGinnis, G.K.G. Hohenwarter, M. Ketkar, J.B. Beyer and J.E. Nordman

Summary: A niobium-based superconducting amplifier consisting of a series array of 60 vortex flow transistors (VFT) was fabricated and tested. Each VFT consisted of a long Josephson junction biased in the flux flow state, magnetically coupled to a current based on a distributed amplifier configuration. The transresistance of the amplifier in a 50- Omega environment for frequencies up to 1 MHz was measured. The transresistance of the array was less than the expected value calculated from measurements obtained on a single VFT. The difference was probably due to nonuniformities in the fabrication process, which caused some of the junctions not to be biased in the flux flow state or receive the same amount of magnetic field from the control line. However, measurements of the array showed that a large number of VFTs could be connected in series and simultaneously be biased into the flux flow state.
A modified superconducting current injection transistor and distributed amplifier design

   D.P. McGinnis, J.B. Beyer and J.E. Nordman

Summary: The authors have modified the design of the superconducting current injection transistor (Super-CIT) for use in a distributed amplifier. The super-CIT consists of a resistively damped long Josephson junction in which the maximum Josephson current is modulated by the magnetic field produced by current in a control line. The device is modified by DC-coupling the control line from the Josephson junction so that the Super-CIT can be embedded in a distributed amplifier configuration. The distributed amplifier design is used to raise the input impedance and the power gain of the amplifier over a wide bandwidth. The small signal current gain of the device can be increased by biasing the Josephson junction in an asymmetric configuration. A simulation using practical values results in an amplifier with an input impedance of 6.5 Omega using only four devices, which produces 15 dB of gain into a 2.5- Omega load over a bandwidth of 90 GHz with very little reverse gain.
Performances of a flux-flow-type Josephson amplifier

   T. Hashimoto, K. Enpuku and K. Yoshida

Summary: The authors have been developing an analog amplifier utilizing a flux flow phenomena in a Josephson line, i.e. the flux-flow-type Josephson amplifier (FFA). The FFA converts a signal current I/sub s/ to a voltage V/sub dc/ across the Josephson line, and the I/sub s/-V/sub dc/ characteristic determines the performance of the FFA, e.g. the gain and saturation level. Studies have been made to improve the I/sub s/-V/sub dc/ relation. It is shown that the transresistance can be improved significantly by reducing the width of the Josephson line and increasing the kinetic inductance of the line. The kinetic inductance can be increased by thinning the line electrode and by using an electrode with large London penetration depth, such as NbN. The transresistance obtained is as large as 6.8 Omega for NbN/Pb-alloy Josephson lines with a thickness of 5 nm and a width of 4 mu m. It is also shown that the linear operating range of the amplifier is as large as 1 mV.
Experiment of filed-effect transistor with a channel made of NbN granular thin film

   M. Sugahara, N. Yoshikawa and T. Murakami

Summary: The authors describe an experimental study of the effect of an electric field on a granular superconducting thin film using a three-terminal device which has the structure of a field-effect transistor, with the channel made of NbN granular thin film. When the gate voltage is varied at low temperature, the channel resistance shows a cyclical variation of more than one cycle. The maximum resistance variation observed at 4.2 K is about 40% . The voltage period for the resistance variation seems to correspond to the induction of the electric pair charge, 2e, on a grain. It is concluded that this result is due to a new microscopic quantum effect dual to the Josephson effect and could lead to a novel three-terminal superconductor device.
Prospects for proximity effect superconducting FETs

   A.W. Kleinsasser and T.N. Jackson

Summary: The authors address the question of how a JOFET (Josephson field effect transistor) works and whether or not a useful device of this type is feasible. They show that JOFETs represent a limiting case of normal FETs in which superconducting source and drain contacts result in zero channel resistance. This results in improved device characteristics, but does not have a major effect on speed or power dissipation. With conventional superconductors, the input and output voltage scales are incompatible, but the authors describe the extent to which this can be overcome by using high-temperature superconductors, making possible voltage gain exceeding unity. Device length and operating temperature are constrained by the natural length scale for the penetration of superconductivity into normal materials, so that submicrometer device dimensions and operating temperatures less than approximately 77 K are required. Silicon is effectively ruled out in favor of III-V materials for device operation above approximately 20 K.
Noise model for the superconducting-base semiconductor-isolated transistor

   A. Davidson and D.J. Frank

Summary: A simple noise model for bipolar transistors is adapted to the superconducting base semiconductor isolated transistor (SUBSIT). The model includes two statistically independent shot noise current sources in a lumped element model. For the case where the emitter of the SUBSIT is a normal metal, it is shown that the bipolar model carries over intact. For a SUBSIT with a superconducting emitter as well as base, the noise performance improves tremendously, due to the sharper turn-on characteristic. Noise temperatures in the milli-Kelvin regime are possible, and the energy resolution is likely to be quantum-limited.
Gap measurement in Nb/NbO/sub x//Al injection controlled planar three terminal devices

   K. Takeuchi and Y. Okabe

Summary: The characteristics of Nb/NbO/sub x//Al injection-controlled planar three-terminal superconducting devices (injection-controlled links) have been studied experimentally. A built-in Nb/AlO/sub x//Nb Josephson junction is used to perform direct tunneling measurement, whose results show that the gap in the Nb strip decreases as its critical current is suppressed. It is also shown that the static characteristics of the devices with high and low injector resistance can be fitted to a simple heating model and a modified heating model, respectively.
The circuits of phase-quantum-tunneling device

   N. Yoshikawa, M. Sugahara and T. Murakami

Summary: The authors analyze the dynamics of logic gates and a discrete transmission line composed of PQT (phase-quantum-tunneling) junctions, each of which has characteristics completely dual to those of the Josephson junction. A PQT transistor which is represented as a series connection of two PQT junctions has a periodic threshold-voltage-charge relation with a period 2e. It is shown that it is possible to construct a PQT inverter and other PQT logic gates similar to the FET logic gates. The PQT logic gates have high performance (high switching speed and low power dissipation) even in high-temperature operation. Charge-soliton logic circuits can be formed using discrete PQT transmission lines. It is concluded that PQT devices are highly suitable for high speed electronics using high-T/sub c/ superconductors.
Superconductor electronics: new prospects

   K.K. Likharev, V.K. Semenov and A.B. Zorin

Summary: The authors review research on superconductance electronics carried out at Moscow State University. It is shown that the utilization of high-T/sub c/ superconductors allows cheaper but hardly more perfect electronic components and devices, so that the discovery of these superconductors is expected to have the largest impact on the practical use of the simplest components, such as EMF (electromagnetic field) shields, microwave modulators, SQUIDs (superconducting quantum interference devices), and samplers. Superconducting LSI (large scale integrated) circuits, including multijunction voltage standards, A/D (analog/digital) and D/AS (digital/analog) converters, and digital signal processors, although less affected by the new materials, nevertheless are expected to benefit from other recent ideas and results, in particular, the invention of the RSFQ (resistive or rapid single flux quantum) logic circuit family and the discovery of correlated single-electron tunneling.
NbN/MgO/NbN Josephson tunnel junctions fabricated on thin underlayers of MgO

   G.L. Kerber, J.E. Cooper, R.S. Morris, J.W. Spargo and A.G. Toth

Summary: Underlayers of MgO as thin as 8.0 nm have been used in the fabrication of NbN/MgO/NbN Josephson tunnel junctions. NbN/MgO/NbN trilayers with and without MgO underlayers were deposited on thermally oxidized Si substrates at 100 degrees C using RF magnetron sputtering in a semi-UHV (ultrahigh vacuum) load lock vacuum system. Sputtering parameters were first optimized to produce NbN with T/sub c/=14.7 K on SiO/sub 2//Si substrates, and then thin MgO underlayers were used to enhance the T/sub c/ of the trilayers to 15.7 K. X-ray diffraction of NbN films indicates that thin MgO underlayers of 8.0 nm are capable of almost completely removing the NbN [111] diffraction peak found in lower T/sub c/ films and enhancing the NbN [200] peak. MgO underlayers were found to be oriented in the [100] direction when sputtered in an atmosphere of Ar and N/sub 2/ and randomly oriented when sputtered in Ar alone. The authors present details for the preparation and analysis of NbN and MgO films as well as the fabrication and electrical performance of tunnel junctions with and without MgO underlayers.
The observation of the AC Josephson effect in a YBa/sub 2/Cu/sub 3/O/sub 7//Au/YBa/sub 2/Cu/sub 3/O/sub 7/ junction

   B. Schwartz, P.M. Mankiewich, R.E. Howard, L.D. Jackel, B.L. Straughn, E.G. Burkhart and A.H. Dayem

Summary: The authors have demonstrated proximity effect coupling between a high-transition-temperature superconductor and a normal metal. In a device with a 1- mu m long gap in a YBa/sub 2/Cu/sub 3/O/sub 7/ film spanned by an Au shunt, the authors observed a DC supercurrent and the AC Josephson effect under microwave irradiation from 2 GHz to 15 GHz. Preliminary work has also begun with Ag shunts. It is concluded that these high quality S-N (superconductor-normal) interfaces should be applicable both to probing the superconducting state in oxide superconductors and to building high-T/sub c/ electronic devices.
Low temperature synthesis of Y-Ba-Cu oxide films and preparation of DC-SQUIDs

   M. Matsuda, A. Matachi and S. Kuriki

Summary: The authors have synthesized superconducting Y-Ba-Cu oxide thin films by RF sputtering at a relatively low substrate temperature (about 650 degrees C). Films of 300-700 nm thickness have Tc of 60-72 K without annealing after the deposition. A preferential orientation with a c-axis perpendicular to the surface was observed. DC SQUIDs (superconducting quantum interference devices) having two parallel microbridges with constriction of submicrometer to 40- mu m width were fabricated from the oxide films by chemical etching. The microbridges with greater than 2- mu m-width did not operate as Josephson devices. The characteristics of these SQUIDs suggested vortex flow. Periodic modulation of the voltage with magnetic flux was observed in a SQUID having submicrometer microbridges. Telegraph-like noise of the voltage which exhibits switching between two or more discrete levels was observed in all of the SQUIDs irrespective of the width of the microbridges. This noise was also observed in a single microbridge, and its effective switching rate increased exponentially with the increase of temperature above 15 K.
Characterization of a high temperature superconducting oxide thin-film RF SQUID

   K.P. Daly, A.H. Silver, R.W. Simon, C.E. Platt, A.E. Lee, M.S. Wire and J.E. Zimmerman

Summary: The authors have successfully fabricated and operated RF SQUIDs (superconducting quantum interference devices) made from thin films of the high-temperature superconducting oxide ErBa/sub 2/Cu/sub 3/O/sub 7-x/. The ideal triangular quantum interference pattern characteristics of RF SQUIDs are observed. The performance of a particular device, operating between 60 and 65 K, is described in detail. Except for a possible increase of noise due to operation close to T/sub c/, the limited temperature range is shown to have no decisive practical disadvantage. The precise nature of the Josephson coupling in the device is unclear. It seems likely that Josephson coupling occurs between individual grains and probably within the microbridge.
Fabrication of submicrometer features in Y-Ba-Cu-O superconducting thin films

   C.T. Rogers, T.L. Cheeks, P. England, S.-W. Chan, H.G. Craighead and T. Venkatesan

Summary: The authors explored some of the processes required to fabricate superconducting devices in Y-Ba-Cu-O thin films. Photolithography was used to define superconducting wires with dimensions from several micrometers to less than one micrometer in films grown both by laser and electron-beam deposition. Patterns were transferred with a variety of techniques including lift-off, chemical etching, and argon ion milling. Low-resistance contacts were reliably made by in situ Ar ion beam presputter and Au or Ag deposition. Submicrometer wires produced with these processes behaved as scaled-down bulk superconducting films; wire properties were determined largely by initial film morphology and wire geometry. No naturally occurring weak link behavior was observed in wires down to 0.5 mu m in width. The fabrication process and the electrical behavior of the resulting wires are discussed.
Critical currents in a high-T/sub c/ superconducting short dipole antenna

   C.E. Gough, S.K. Khamas, T.S.M. Maclean, M.J. Mehler, N.M. Alford and M.M. Harmer

Summary: Measurements on a liquid-nitrogen-cooled, superconducting short-dipole aerial at 550 MHz are presented. The measured relative field strength as a function of frequency is shown for an excitation current well below the critical value. The field strength is shown as a function of frequency for input powers of 25 dBm, 28 dBm, and 31 dBm. An estimate of the RF critical current is made from deviations in linearity with input power.
Photoconductive response of granular superconducting films

   U. Strom, E.S. Snow, R.L. Henry, P.R. Broussard, J.H. Claassen, S.A. Wolf, M. Leung and R.W. Simon

Summary: The application of a DC magnetic field to disordered or granular films of Y-Ba-Cu-O is shown to lead an enhancement of a nonbolometric photoresponse at temperatures near and below T/sub c/. The disorder is evidenced by the broadened resistive transition to superconductivity and by the higher normal state resistance of the films. This observation is consistent with a nonequilibrium effect, which is described by the flux-flow model of the low-temperature photoresponse of granular superconductors.
Optical detection by suppression of the gap voltage in niobium junctions

   D.P. Osterman, M. Radparvar and S.M. Faris

Summary: The application of niobium Josephson junctions as detectors in infrared focal plane arrays is being investigated. The dependence of the optical response of these junctions on several variables including temperature, frequency of light chopping, and light intensity has been measured. In addition the authors have investigated the effect of different substrate materials, namely, single-crystal silicon and amorphous fused quartz, and the effect of two different cryogenic environments, namely, vacuum and superfluid helium. For measurements in vacuum, cooling is provided by contact between the substrate and a cold surface. Immersion in superfluid helium is expected to reduce heating effects considerably owing to its extremely high thermal conductivity, thus isolating nonequilibrium effects. The NEP (noise equivalent powers) and D* (detectivity) of the detectors is limited by noise in the room-temperature electronics. For a typical niobium junction of area 100 mu m/sup 2/ on a fused quartz (SiO/sub 2/) substrate in vacuum at 4.2 K the responsivity is 3000 V/W, NEP is 6*10/sup -13/ W, and D* is 2*10/sup 9/ cm-Hz/sup 1/2//W for a 1-Hz bandwidth at a wavelength of 1 mu m.
Optical response of YBCO thin films and weak-links

   D.P. Osterman, R. Drake, R. Patt, E.K. Track, M. Radparvar and S.M. Faris

Summary: The authors have fabricated films of the high-temperature superconductor YBCO and measured their response to optical and infrared radiation. The response is manifested by a change in the current-voltage characteristics of YBCO weak links. The change is found to be dependent on film quality, operating point, light chopping frequency, and temperature. Depending on the type of anneal, the superconducting films exhibit metallic or semiconducting resistivity behavior above T/sub c/. The optical responsivity of semiconducting films is larger than that of metallic films. By further annealing, semiconducting films could be converted into metallic films with a concurrent decrease in their optical responsivity. Some of the measurements have been performed with the films immersed in superfluid helium to allow the separation of nonequilibrium effects from the equilibrium bolometric response. The results of this preliminary study indicate that patterned YBCO films in the superconducting state can be used as sensitive detectors of light.
Optical response of epitaxial and granular films of YBa/sub 2/Cu/sub 3/O/sub 7- delta/ at temperatures from 25 K to 100 K

   M.G. Forrester, M. Gottlieb, J.R. Gavaler and A.I. Braginski

Summary: The authors present the results of optical detection in epitaxial and granular films of YBa/sub 2/Cu/sub 3/O/sub 7- delta / at wavelengths of 0.63, 3.39, and 10.6 mu m and at temperatures from 25 K to 100 K. Both types of film exhibit only bolometric detection, with no evidence for nonequilibrium effects in this temperature range. For 0.63- mu m radiation, mechanically chopped at 725 Hz, measurements of a 10*90 mu m/sup 2/ epitaxial bridge yield a bolometric responsivity of approximately 4*10/sup 3/ V/W, and detectivity D* of more than 10/sup 8/ cm square root Hz/W. Granular films biased above their critical current are found to exhibit two-level switching noise, resulting in Lorentzian deviations from an otherwise 1/f noise spectrum.
Superconducting kinetic inductance bolometer

   J.E. Sauvageau and D.G. McDonald

Summary: The authors are developing a bolometer with a temperature sensor based on the temperature dependence of the inductance of a superconducting microstrip line. As a first step in exploring this idea experimentally, they have designed experiments to test only the temperature sensor. The experimental devices are all-niobium inductance thermometers fabricated on silicon substrates which have been deeply etched to provide areas of relative thermal isolation. The ground plane superconductor is thin enough so that its kinetic inductance dominates the audio frequency impedance of the stripline near its critical temperature, at 0.9 T/sub c/. This differential thermometer uses a commercial SQUID (superconducting quantum interference device) as the preamplifier. Preliminary results demonstrate a proof-of-principle for the thermometer design. An important quality factor for this type of measurement system is the depth of the null. The authors achieved a high value of 0.4*10/sup -6/, which is satisfying for a first try.
The high T/sub c/ superconducting bolometer

   P.L. Richards, S. Verghese, T.H. Geballe and S.R. Spielman

Summary: A description is given of the optimization of a bolometric infrared detector which uses the resistive transition of a high-T/sub c/ film as the thermometer. The performance of an LN (Liquid nitrogen)-cooled far-infrared bolometer operated with a cooled low-pass filter is computed for the ideal case of a noise-free readout. The theory is then extended to include various contributions to the readout noise. Measurements are presented of the low frequency noise near T/sub c/ in current-biased films of ErBa/sub 2/Cu/sub 3/O/sub 7/, which show that useful performance can be achieved. Comparisons are made with other infrared detection technologies which show that practical high T/sub c/ bolometers will be especially useful for wavelengths longer than the -20 mu m cutoff of LN-cooled photovoltaic detectors. Potential applications include far-infrared laboratory spectroscopy and passively cooled space observations of bright sources such as the earth.
Josephson junctions as ultrafast nuclear particle detector

   R. Cristiano and P. Silvestrini

Summary: The problem of optimizing Josephson junction parameters to realize a fast particle (radiation) discriminator is discussed. The switching operation is investigated, focusing on problems of intrinsic noise and nonequilibrium processes induced by the radiation. The key concept is the effective radiation flux, namely, the flux which produces a number of switchings equal to that produced by intrinsic noise. This quantity gives a direct measure of the device performance. The effects of some relevant junction parameters, such as the junction area, the Josephson current density, and the bath temperature, on the behavior of the effective flux as a function of the response time of the device are presented.
Characteristics of high-transmission-probability tunnel junctions for use as particle detectors

   D.A. Stricker, G.P. Alba, C.C. Anderson, D.D. Bing, R.W. Bland, S.C. Dickson, T.G. Dignan, P. Gagnon, R.T. Johnson and C.M. Seneclauze

Summary: Interest in the problem of the galactic dark matter has stimulated development of particle detectors sensitive to very low energies. The authors describe superconducting tunnel junctions with thin barriers which may be suitable for this purpose. They present I-V (current-voltage) characteristics and data on the temperature dependence of the subgap tunneling current. They examine the barrier transmission probability and the resistance of the null junction. They also present some scanning-electron-microscope observations of the thin films of the tunnel junctions, which show that faster deposition produces smaller grains and increasing film thickness results in larger grains from an apparent fusing of smaller grains.
Phonon-mediated detection of X-rays in silicon crystals using superconducting transition edge phonon sensors

   B.A. Young, B. Cabrera, A.T. Lee, C.J. Martoff, B. Neuhauser and J.P. McVittie

Summary: The authors present data on the operation of thin-film superconducting strips of titanium as phonon sensors on the surface of silicon crystals. The superconducting films are biased at the foot of the resistive transition in temperature and below the critical latching current (the current above which a normal region in the film grows from self-heating). The interaction of an incident X-ray in the Si crystal generates a phonon source which propagates to the surface at the speed of sound. Such an event produces a several-microsecond-long self-terminating voltage pulse which is proportional to the amount of the sensor area driven normal. It is shown that these Ti superconducting transition edge sensors operated at 0.3 K have sufficient resolution for detecting particles with energy deposition above several keV, which makes them good candidates for use in neutrino (and other) experiments.
The detection of 6 keV X-rays with Nb junctions

   P. Gare, R. Englehardt, A. Peacock, D. Twerenbold, J. Lumley and R.E. Somekh

Summary: Refractory metal Nb/Al/Al-oxide/Al/Nb junctions are shown to be sensitive to 6-keV X-rays over the temperature range from 2.8 to 1.4 K. For such junctions, which have an observed minimum ionizing energy of 12 MeV, a limiting energy resolution of 8 eV is predicted. Currently an energy resolution of 250 eV is observed at 1.4 K which is primarily dominated by system electronic noise. The Nb-based junctions are shown to be very stable with respect to thermal cycling while the nonequilibrium physics can be simply scaled from the theory of Sn junctions. It is concluded that on-chip arrays having a broad band pass and good energy resolution should be feasible to construct.
Characteristics of Nb-based Josephson junctions at a temperature below 1 K

   K. Ishibashi, K. Takeno, Y. Oae, T. Sakae, Y. Matsumoto, A. Katase, S. Takada, H. Akoh and H. Nakagawa

Summary: A lithographic technique for Josephson LSI (large scale integrated) circuits was applied to the production of a superconducting tunnel junction for radiation detection. Nb-Al/aluminum oxide/Nb tunnel junctions with different junction sizes and barrier oxidation times have been fabricated. The current-voltage curves were measured in the temperature range from 4.2 to 0.45 K. The junctions showed some amounts of leakage current, which remained below 2 K. The behavior of the leakage current was successfully understood from its experimental dependence on the junction size.
A RF superconducting electromechanical transducer for gravitational wave antennae

   M.F. Bocko, W.W. Johnson and V. Iafolla

Summary: An electromechanical transducer based on a superconducting radiofrequency bridge circuit has been developed for use on a gravitational radiation detector. The low electrical loss of superconductors has made it possible to achieve electrical quality factors of several thousand in a lumped-element circuit which operates at 4 MHz. The bridge could be remotely balanced to one part in 50000, which led to a displacement noise level of 10/sup -15/ m/ square root Hz. It should be useful in measuring any physical quantity which can be made to change a capacitance. At the present stage of development, capacitance changes of 10/sup -20/ F could be detected in a 1-s integration time. One straightforward improvement, namely, the use of a low-phase-noise quartz crystal oscillator as the bridge excitation source will reduce the noise to 10/sup -17/ m/ square root Hz.
Superconducting microwave resonators for physics experiments

   N. Klein, G. Muller, H. Piel and J. Schurr

Summary: Superconducting resonators at K-band frequencies have been developed for different applications in general physics. Niobium pillbox cavities have been built for the one-atom maser experiment by which the interaction of Rydberg atoms with single microwave photons has been investigated. At 21.5 GHz and 1.3 K, quality factors of up to 10/sup 11/ were obtained. Coating of the cavity with Nb/sub 3/Sn resulted in quality factors of 6*10/sup 8/ at 4.2 K and 6*10/sup 9/ at 2 K. A superconducting Fabry-Perot resonator consisting of two spherically curved niobium mirrors was also investigated. The quality factor of 1.8*10/sup 7/ measured at 25 GHz and 4.2 K was found to be two orders of magnitude higher than for a corresponding copper resonator. Fabry-Perot resonators can be used for detecting small position changes for one mirror with respect to another caused by gravitational forces. First experiments with copper Fabry-Perot mirrors suspended in a vacuum chamber provided a maximum sensitivity for a gravitational acceleration of one mirror of 4*10/sup -11/ m/s/sup 2/. These results are promising for a possible fifth force detector based on a superconducting Fabry-Perot resonator.
Dual channel 115 and 230 GHz SIS receivers in operation at the Owens Valley Radio Observatory

   D.P. Woody, C.J. Giovanine and R.E. Miller

Summary: The Owens Valley Radio Observatory millimeter-wave interferometer array is presently operating with dual-channel SIS (superconductor-insulator-superconductor) tunnel junction receivers. The first channel covers the frequency range from 85 to 120 GHz and the second channel covers the frequency range from 200 to 300 GHz. The mixers consist of a corrugated feed horn, a single-stage circular-to-rectangular waveguide transition a reduced-height waveguide with an SIS junction mounted across the E-plane, and a non-contacting backshort. The mixer block has a built-in RF choke for the IF (intermediate frequency) signal path which is designed to present a short circuit to the junction at frequencies above the 2-GHz IF frequency. The small-area (<1 mu m/sup 2/) PbInAu-native oxide-PbAu SIS tunnel junctions are fabricated using a bridge lift-off technique. The receivers in the 85- to 120-GHz band have noise temperatures of <100 K, while the receivers in the 100- to 300-GHz band have noise temperatures in the range from 200 to 300 K. These dual-channel receivers are mounted in 4.5 K closed-cycle refrigerators and are in continuous use on the array.
Observation of 4.2 equilibrium noise squeezing via a Josephson-parametric amplifier

   B. Yurke, P.G. Kaminsky, R.E. Miller, E.A. Whittaker, A.D. Smith, A.H. Silver and R.W. Simon

Summary: The authors observed the squeezing of 4.2 K thermal noise using a Josephson parametric amplifier operated in the degenerate mode at 19.4 GHz. A 42% reduction in the equilibrium noise was observed. The amplifier has also been operated at 0.1 K with an excess noise of 0.28 K referred to the amplifier's input port. This is less than the vacuum fluctuation noise of 0.47 K at the amplifier's input. Recently the amplifier has been operated in a nonchaotic mode with a signal gain in excess of 16 dB.
Beating the quantum limit in SIS mixers

   M.J. Wengler and M.F. Bocko

Summary: The 2LO (double local oscillator) mixer is analyzed in the low-LO-power limit for a perfect SIS (superconductor-insulator-superconductor) diode. It is shown that a 2LO SIS mixer can beat the noise performance of a one-LO mixer by a factor of two. It is suggested that even lower noise is possible with an SIS when operated in some other way.
MM wave quasioptical SIS mixers

   Q. Hu, C.A. Mears, P.L. Richards and F.L. Lloyd

Summary: The authors have tested the performance of planar SIS (superconductor-insulator-superconductor) mixers with log-periodic antennas at near millimeter and submillimeter wave frequencies from 90 to 360 GHz. The large omega R/sub N/C product ( approximately 10 at 90 GHz) of the Nb/NbO/sub x//Pb-In-Au junctions requires an integrated inductive tuning element to resonate the junction capacitance at the operating frequencies. Two types of integrated tuning element were used which were designed with the aid of measurements using a Fourier transform spectrometer. Preliminary results indicate that the tuning elements can give very good mixer performance up to at least 200 GHz. An inductive wire in parallel with a 5-junction array gives a minimum mixer noise temperature of 115 K (DSB) at 90 GHz with a FWHM (full width at half maximum) bandwidth of 8 GHz. An open-ended microstrip stub in parallel with a single junction gives minimum mixer noise temperatures at 150 and 200 K (DSB) near 90 and 180 GHz with FWHM bandwidths of 4 and 3 GHz, respectively. The relatively high mixer noise temperatures compared to those of waveguide SIS mixers in a similar frequency range are attributed mainly to the losses in the optical system.
Josephson terahertz local oscillator

   R.P. Robertazzi and R.A. Buhrman

Summary: Voltage-tunable Josephson junction terahertz oscillators have been fabricated using rugged, high-current-density NbN/sub 1-x/C/sub x/ tunnel junctions with M O barriers. The radiation emitted from such junctions is detected on chip by a second Josephson junction which is capacitively coupled to the first. For oscillator junctions with a critical current density of J/sub c/ approximately 3.5*10/sup 4/ A/cm/sup 2/ the junction oscillates with a voltage amplitude of approximately=1.5 mV. The detected RF voltage level remain essentially constant from 300 GHz to above 1 THz, the upper limit of the detector. From measurements of the Josephson step height in the detector current-voltage characteristics, it is determined that the oscillator junction produces 0.5 mu W of terahertz radiation of which, due to impedance mismatch, 10 nW is coupled into the detector junction.
A current controlled variable delay superconducting transmission line

   S.M. Anlage, H.J. Snortland and M.R. Beasley

Summary: The authors present a device concept for a superconductive current-biased variable-delay transmission line structure which is capable, in principle, of operating up to the terahertz regime. The device makes use of the change in kinetic inductance of superconductors with transport current. The relevant material figures of merit for optimum performance of such a device are defined, and suitable candidate materials are identified. The device concept has been tested in niobium technology, where temperature-dependent changes in the inductance are easily achieved. Preliminary measurements on the temperature and current dependence of niobium transmission line resonators operating in the 1-20 GHz range are presented. The expected DC bias current variable delay has not yet been observed, but niobium is not expected to be the optimum material for such an effect. Suggested improvements include the use of more favorable materials, such as amorphous alloys and oxide superconducting films, and the use of modified microstrip geometries where a closer approach to the depairing critical current density should be possible.
Picosecond switching dynamics of a Josephson tunnel junction

   D.R. Dykaar, R. Sobolewski and T.Y. Hsiang

Summary: The authors previously reported (D.R. Dykaar et al., 1987) switching measurements of a tunnel junction excited by photogenerated picosecond current pulses. The junction was found to switch from the zero- to the finite-voltage regime for subcritical current pulses, and the results were modeled with a critical charge concept. It is shown that in addition to pulse charge, pulse risetime is a critical parameter in determining the junction response. Simulations have been performed using exponentially rising and failing pulses to simulate the experimentally measured waveform. Significant deviations from DC behavior have been found. Pulse risetime has been found be the parameter which causes the onset of the observed chaos in these devices. Pulse falltime has no effect, which is consistent with the critical risetime interpretation.
Noise characteristics and instabilities of long Josephson junctions

   B.S. Han, B. Lee, O.G. Symko, W.J. Yeh and D.J. Zheng

Summary: The noise characteristics and chaotic behavior of long Josephson junctions in a magnetic field are investigated. In a magnetic field, current-biased junctions exhibit the dynamics of fluxon motion affected by fluctuations. These consist of telegraph noise at voltage steps and instabilities due to chaotic behavior. Results on long junctions with McCumber number ranging from 10 to 100 show such behavior. The telegraph noise is driven by thermal fluctuations. Modeling of the junctions using a perturbed sine-Gordon equation shows chaotic and periodic regions. Some of the chaotic regions are between Fiske steps, while others are at the edge of the Fiske steps. These observations are confirmed by numerical calculations.
Chaos and catastrophe near the plasma frequency in the RF-biased Josephson junction

   R.L. Kautz and R. Monaco

Summary: The authors examine two forms of complex behavior in the RF-biased junction that occur at bias frequencies near the plasma frequency: the chaotic instabilities that influence the design of voltage standards; and a cusp catastrophe. Using digital simulation the authors determine how chaos and catastrophe affect the zero-voltage part of the I-V (current voltage) curve as a function of the RF amplitude and frequency. In particular, they show that chaotic instabilities result in discontinuities in the DC-bias range of the zero-voltage state and the cusp catastrophes result in two dynamically different zero-voltage states that exist over the same DC-bias range. They also report the experimental verification of the former effect.
Studies of chaos and thermal noise in a driven Josephson junction using an electronic analog

   C.M. Pegrum, W.S.C. Gurney and R.M. Nisbet

Summary: Using an electronic analog of a resistively shunted driven Josephson junction, the authors have demonstrated a number of effects, including the appearance of a devil's staircase in the current-voltage characteristic, the onset of chaos, and the effect of noise on these phenomena. It is stressed that the analog is simple, but models the junction behavior with a high degree of accuracy and detail.
Dynamic stabilization of a microwave-driven Josephson tunnel junction against a period-doubling bifurcation

   J.B. Hansen, G.F. Eriksen, M.R. Samuelsen and H. Svensmark

Summary: The authors present theoretical and experimental results on the effect of periodic perturbations on microwave-driven Josephson tunnel junctions close to a period-doubling bifurcation. The theory, which is quite general, describes how a periodic near-resonant perturbation changes the stability of the system. The phenomenon was investigated experimentally in small Nb-NbO/sub x/-Pb tunnel junctions, and experimental findings were found to be in agreement with the theory. The effect has importance for the performance of parametric amplifiers based on Josephson tunnel junctions.
Mutual locking, chaos and devils staircase in two Josephson tunnel junctions with a common resistive shunt

   H.D. Jensen, A. Larsen, J. Mygind and M.T. Levinsen

Summary: The authors studied the phase-locking in a pair of individually biased, resistively and capacitively shunted Josephson junctions, coupled by a common resistive or capacitive shunt, on an analog computer. Under certain conditions, locking is found to occur at all rational frequency ratios. A critical line is found in parameter space along which the steps form a complete devil's staircase having a fractal dimension of 0.87. Beyond the critical line bifurcations occur on all steps following the Feigenbaum sequence to chaos. The Feigenbaum constants are recovered to a fair accuracy. Preliminary experiments with two Josephson tunnel junctions shunted on the chip by a gold-indium film are discussed.
Experimental results on the metastability of the resistive state in Josephson junctions

   R. Cristiano, S. Pagano and P. Silvestrini

Summary: The authors report experimental results on the metastability of both the V=0 and the V not=0 states in Josephson junctions. A comparative analysis of both the decay mechanisms at various values of the Josephson coupling energy makes it possible to obtain useful information on the relevant parameters in the lifetime expression of the V not=0 state. In particular, cases were investigated where the lifetime of the V=0 state is comparable with the lifetime of the V not=0 state. This situation is experimentally realized by applying an appropriate magnetic field. Experimental data show good agreement with theory for junctions with a low level of damping. As the hysteresis parameter increases, discrepancies appear.
Structure of resistive networks for dispersive tunnel processes

   G. Brunk, C. Zurbrugg and H. Lubbig

Summary: Fundamental construction principles for equivalent circuits for superconducting pair and quasiparticle tunnel junctions are discussed. To the lowest order of microscopic tunneling, the two basic features of the corresponding macroscopic dynamics, i.e the energy-neutral nonlinear self-coupling of the quantum phase shift and the energy-effective tunnel admittance, are discussed in the framework of linear response theory (equivalent to the KUBO formalism) and are represented by means of the corresponding equivalent two-subcircuit network. Approximation formulas describing a singularity-equivalent model are discussed in detail, and consequences for secondary quantum processes are indicated.
Anomalously large Josephson switching currents in low dissipation Josephson junctions

   C.D. Tesche, J.R. Kirtley, W.J. Gallagher, A.W. Kleinsasser, R.L. Sandstrom and S.I. Raider

Summary: The authors observed marked effects on the switching characteristics of a high-quality junction due to the frequency dependence of the external circuitry. This involved anomalously high values of the maximum switching current of Josephson junctions at temperatures where thermally activated switching was expected to greatly lower it. This effect was modeled by evaluating junction parameters from the measured characteristics. The junction resistance determined from the return switching current is that of a nearly ideal quasiparticle tunneling resistance, increasing exponentially fast at low temperatures. As a result, the load resistance becomes dominant over a wide range of temperatures. The frequency dependence of this load resistance then produces the anomalously large Josephson switching currents, which have not been observed previously in junctions with significant normal conductance.
Dynamical study of the superconducting phase transition of two-dimensional networks

   B. Jeanneret, P. Fluckiger, C. Leemann and P. Martinoli

Summary: Granular aluminum wire networks forming square arrays of N*N approximately=10/sup 6/ nodes connected by strips of 8- mu m long were fabricated with photolithographic techniques. For strip resistances of the order of 1 k Omega the superconducting transition of the network, as evidenced by AC conductance measurements is shown to be of the Kosterlitz-Thouless type. In a perpendicular magnetic field, flux quantization in the loops of the network leads to periodic oscillations of the magnetoconductance.
DC voltage multipliers: a novel application of synchronization in Josephson junction arrays

   V.K. Semenov and M.A. Voronova

Summary: New types of followers and follower/doublers of DC voltage are proposed and analyzed. Operation of the devices is based on synchronization of the single-flux quantum (SFQ) pulses generated by overdamped Josephson junctions coupled by means of passive capacitive or inductive circuits. Two ways of combining the followers and doublers to get DC voltage multipliers and standards are described. Possible applications of these devices in A/D and D/A converters and RSFQ (rapid SFQ) logic circuits are also discussed. It is believed that the proposed multipliers and standards could produce stable output voltages in the 1-10 V range with output currents in the 0.1-1 mA range.
Single-electron tunnel junction array: an electrostatic analog of the Josephson transmission line

   K.K. Likharev, N.S. Bakhvalov, G.S. Kazacha and S.I. Serdyukova

Summary: The authors carried out static and dynamic analyses of uniform one-dimensional arrays of ultrasmall tunnel junctions. The correlated single-electron tunneling in the junctions of the array results in a behavior qualitatively similar to that of the Josephson transmission line. In particular, external electric fields applied to the array edges can inject single-electron-charged solitons into the array interior. The shape of such a soliton and the character of its interactions with other solitons and the array edge are very similar to those of Josephson vortices (sine-Gordon solitons) in the Josephson transmission line. Under certain conditions, a coherent motion of the soliton train along the array is possible, resulting in generation of narrowband SET (single-electron tunneling) oscillations with frequency f=/e, where is the DC current flowing along the array.
Multi-fluxon dynamics in inhomogeneous Josephson junctions: experiment

   A.V. Ustinov

Summary: Long Nb-NbO-Pb Josephson junctions with artificially formed SiO inhomogeneities in the insulator layer have been studied. A fine structure has been observed on the current-voltage characteristics of the junctions. Such structure is considered to be due to the resonant interaction between the fluxon and its radiation. The single-fluxon effect in the zero magnetic field and the multifluxon effect in a large field have been studied experimentally. The results are compared with those of the perturbation theory and numerical simulation. A multifluxon-chain pinning effect observed in the commensurable lattice of inhomogeneities is reported and discussed.
Status of the SSC superconducting magnet program

   J. Peoples

Summary: The Superconducting Super Collider (SSC) is a proposed proton-proton collider designated to achieve collisions with 20 TeV per beam. In the SSC, protons are accelerated and stored in two storage rings that are stacked one on top of the other in an underground tunnel 83 km in circumference. In each collider ring the protons are kept in a roughly elliptical orbit by two types of magnets: dipoles, which bend the proton orbit into a closed loop, and quadrupoles, which deflect the protons back toward the central orbit when they diverge from it. Both types of magnets use high-current superconducting coils to meet the SSC design requirements. A dipole field of 6.6 T was chosen as a compromise between the need for the highest practical field and the limits of superconducting technology. The author reviews the work done on the SSC dipole. Topics discussed are cable development and production, cryostat design, cold mass design, and model magnet testing.
Test results from recent 1.8-M SSC model dipoles

   P. Wanderer, J.G. Cottingham, P. Dahl, M. Garber, A. Ghosh, C. Goodzeit, A. Greene, J. Herrera, S. Kahn, E. Kelly, G. Morgan, A. Prodell, W. Sampson, W. Schneider, R. Shutt, P. Thomspon and E. Willen

Summary: The authors report results for four 1.8-m-long dipoles built as part of the Superconducting Super Collider (SSC) research and development program. Except for length, these models have the features of the SSC design, which is based on a two-layer cosine theta coil with a 4-cm aperture. Compared to the 17-m design-length SSC dipoles, the 1.8-m magnets are faster and more economical way of testing changes in field shape design, conductor support in the coil straight section and ends, etc. The four magnets reported all reach fields in excess of 7.5 T with little training and have excellent field shape.
Tests of full scale SSC R&D dipole magnets

   J. Strait, B.C. Brown, R. Hanft, M. Kuchnir, M. Lamm, R. Lundy, P. Mantsch, P.O. Mazur, A. McInturff, J.R. Orr, J.G. Cottingham, P. Dahl, G. Ganetis, M. Gerber, A. Ghosh, C. Goodzeit, A. Greene, J. Herrera, S. Kahn, E. Kelly, G. Morgan, A. Prodell, W. Sampson, W. Schneider, R. Shutt, P. Thompson, P. Wanderer, E. Willen, S. Caspi, W. Gilbert, R. Meuser, C. Peters, J. Rechen, R. Royer, R. Scanlan, C. Taylor, J. Zbasnik, M. Chapman, A. Devred, J. Kaugerts, J. Peoples, J. Tompkins and R. Schermer

Summary: Four full-scale SSC (Superconducting Super Collider) research and development dipole magnets, incorporating successive mechanical design improvements, have been quench-tested. Three of the magnets are heavily instrumented with sensors to measure their mechanical behavior and verify the effectiveness of the mechanical improvements and with multiple voltage taps to locate the origin of quenches. The last two magnets of this series reach the SSC design operating field of 6.6 T in two or fewer quenches. Load cells and motion sensors show that in these two magnets the azimuthal clamping stress is higher at zero current and drops more slowly with excitation that in previous long magnets, and that the axial motion of the coil upon excitation has been greatly reduced. Quenches are found to originate preferentially in several locations, suggesting other design improvements.
Magnetic field decay in model SSC dipoles

   W.S. Gilbert, R.F. Althaus, P.J. Barale, R.W. Benjegerdes, M.A. Green, M.I. Green and R.M. Scanlan

Summary: The authors have observed that some of the model SSC dipoles have long-time-constant decays of the magnetic field harmonics with amplitudes large enough to result in significant beam loss, if they are not corrected. The magnets were run at constant current at the SSC injection field level of 0.3 Tesla for one to three hours, and changes in the magnetic field were observed. One explanation for the observed field decay is time-dependent superconductor magnetization. Another explanation involves flux creep or flux flow. Data are presented on how the decay changes with previous flux history. Similar magnets with different Nb-Ti filament spacings and matrix materials have different long time field decay. A theoretical model using proximity coupling and flux creep as mechanisms for the observed field decay is discussed.
Measurement of internal forces in superconducting accelerator magnets with strain gauge transducers

   C.L. Goodzeit, M.D. Anerella and G.L. Ganetis

Summary: An improved method has been developed for the measurement of internal forces in superconducting accelerator magnets, in particular the comprehensive stresses in coils and the end restraint forces on the coils. The transducers have been designed to provide improved sensitivity to purely mechanical strain by using bending mode deflections for sensing the applied loads. Strain gauge resistance measurements are made with a new system that eliminates sources of errors due to spurious resistance changes in interconnecting wiring and solder joints. The design of the transducers and their measurement system is presented along with a discussion of the method of compensation for thermal and magnetic effects, methods of calibration with typical calibration data, and measured effects in actual magnets of the thermal stress changes from cool-down and the Lorentz forces during magnet excitation.
Magnet systems for the International Thermonuclear Experimental Reactor

   C.D. Henning and J.R. Miller

Summary: Preliminary parameters for the superconducting magnet system for the International Thermonuclear Experimental Reactor has been established to guide more detailed design work. Radiation tolerance of the superconductors and insulators has been important because it sets requirements for the neutron-shield dimension and sensitively influences reactor size. Major levels of mechanical stress appear in the structural cases of the inboard legs of toroidal-field (TF) coils. The winding packs of the TF coils include significant fractions of steel that provide support against in-plane separating loads, but they offer little support against out-of-plane separating loads unless shear-bonding of the conductors can be maintained. Removal of heat from nuclear and AC loads has not limited the fundamental design, but it has nonnegligible economic consequences.
TORE SUPRA: a tokamak with superconducting toroidal field coils-status report after the first plasmas

   B. Turck

Summary: The technology for TORE SUPRA involves all the problems related to the fabrication and the operation of large cryogenic superconducting coils and of the associated cryogenic system, so is expected to provide significant experience for developing the next generation of machines for controlled fusion. TORE SUPRA has been designed to operate with plasma pulses in excess of 30 s. Operation started in April 1988 with a toroidal field of 2 Teslas. Discharges of 500 kA with a 3-s current flat top were obtained after a few days. Machine parameters where then raised to their normal values (B approximately 4.5 and I/sub p/ approximately 1.7 MA). the discussion covers the goals of the SUPRA, an overview of the basic machine, the conductor the toroidal field coil system, and the cryogenic system.
The design of a high field ohmic heating coil for a superconducting tokamak based on the US-DPC test coil

   M.O. Hoenig and M.M. Steeves

Summary: The fabrication of the US-DPC (demonstration poloidal coil) test coil in the US is using industrial processes capable of manufacturing advanced 30- to 40-kA ternary Nb/sub 3/Sn cable-in-conduit conductors (CICCs) and coils for compact, high-field tokamaks. The authors examine the feasibility of 1- to 1-m-bore 15-T ohmic heating (OH) coils using state-of-the-art CICC conductors. The proof of concept of this technology is expected to be confirmed in the 1990 US-DPC tests at the Japanese Demonstration Poloidal Coil Test Facility. The OH coil design concepts presented appear to satisfy all known superconducting, magnetic, pulsed loss, structural, hydraulic, thermodynamic, and economic requirements of an ohmic heating central solenoid for a compact steady-state tokamak.
Recent progress in the demo poloidal coil program

   H. Tsuji, K. Okuno, H. Nakajima, T. Ando, Y. Takahashi, M. Nishi, K. Yoshida, E. Tada, K. Koizumi, T. Kato, T. Isono, M. Oshikiri, T. Hiyama, K. Kawano, H. Yamamura, M. Sato, J. Yoshida, N. Itoh, S. Shimamoto, T. Satou and T. Ichihara

Summary: The fabrication of two 30-kA NbTi pulsed coils and one 10-kA Nb/sub 3/Sn coil with a total stored energy of 40 MJ is in progress as a part of the DPC (Demonstration Poloidal Coil) Program. All the Nb-Ti superconducting strands have been fabricated, and their loss time-constant has been measured at 0.32 ms at 7 T, which is well below the initial target of less than 1 ms. A novel winding technique is described for the large current conductor which provides good mechanical contact.
Design of the prototype conductors for the Fusion Experimental Reactor

   K. Yoshida, M.F. Nishi, Y. Takahashi, H. Tsuji, K. Koizumi, K. Okuno and T. Ando

Summary: The prototype conductors of the toroidal coil for the Fusion Experimental Reactor have been investigated. Specifications of the conductor are as follows: forced flow cooling; rated current of 30 kA at 12 T and 4.2 K; margin of critical current of 2; current density in winding of 30-40 A/mm/sup 2/; inlet helium at 4.2 K and 4-10 bar; and minimum bending radius of 1.5 m. Three types of conductors were considered as candidates: a test module coil of FF type (hollow cooling type using test module coil Nb/sub 3/Sn conductor techniques); preformed armor type; and advanced disk type. Detailed design parameters and analysis results are given for the three candidate conductors.
Calculation of normal zone propagating velocities and transient thermal effects dependence on the superconducting wire parameters

   J. Casas and L. Rinderer

Summary: Normal phase propagation velocities along superconducting wires immersed in a cooling normal helium bath were investigated experimentally and theoretically. The measurements have been done for bare tin wires with different radii and resistivities. The theoretical calculations of the normal zone propagation velocity versus the circulating current assume a transient mechanism for heat transfer between the wire wall and the normal helium bath. The transient-heat-transfer term is of the form alpha theta /sup 2/ delta theta / delta t, where theta is the temperature relative to the normal helium bath temperature. The transient-heat-transfer coefficient, alpha , is then defined, and good agreement between the theoretical and experimental data is obtained. The coefficient depends on the bath temperature and, nonrandomly, on the maximum power per unit surface released to the normal helium bath, which in turn depends on the wire radius, critical current, and resistivity.
Thermo-electromagnetic stability of ultrafine multifilamentary superconducting wires for 50-60 Hertz use

   A. Fevrier, A. Gueraud, J.P. Tavergnier, Y. Laumond and A. Lacaze

Summary: The authors present calculations of the theoretical thermoelectromagnetic stability of ultrafine multifilamentary superconducting wires. These calculations take into account the self-field effect of the transport current. The authors then compare theoretical and experimental results for conductors comprising typically several hundred thousand 0.17- mu m diameter filaments. These first measurements of the electromagnetic stability of multifilamentary wires under AC conditions have given encouraging results and have shown good agreement with theory. The results are pertinent to the development of Nb-Ti ultrafine filamentary wires for 50-60-Hz applications.
Investigation of the pressure rise during the quench of a force cooled superconducting coil

   Y. Wachi, M. Ono, S. Kimura, A. Tanaka, Y. Sanada, A. Miura and T. Fujioka

Summary: Pressure rise during the quench of NbTi/Cu cable-in-conduit conductor has been experimentally and analytically investigated. The pressure rise under full-length quenching of the conductor is shown to be in good agreement with the calculated pressure rise based on Miller's equation, independently of joule power density. The time elapsed to maximum pressure rise depends on the transport current, which is determined by the joule power density. Pressure rise during quench with a local normal zone strongly depends on the time from the quench to the dump. The measured pressure rise under local quench condition is in good agreement with the calculated value based on L. Dresner's (1986) analytical equation. It is concluded that the maximum pressure rise of a conduit conductor can be restricted by quick discharge in actual fusion magnets.
Analysis of transient thermally-induced convection of supercritical helium in a conduit

   P.E. Phelan, S.M. Kuo and C.L. Tien

Summary: The author investigates the thermally induced transient flow and heat transfer in cable-in-conduit conductors (CICCs) cooled with initially stagnant supercritical helium. Prior studies have demonstrated that thermally induced flow results in a high heat-transfer coefficient and a large thermal stability margin. Accurate prediction of the stability margin requires a quantitative description of the variation of heat transfer with heat flux. This study focuses on the heat-transfer/heat-flux relationship and on the basic mechanisms governing the early stages of transient heating. For modeling the problem is divided into two parts: a low-heat-flux regime and a high-heat-flux regime. Results from the models indicate that the heat-transfer coefficient exhibits a minimum, as observed experimentally in previous study, and that, in general, heat transfer can be considerably enhanced by using a high compressible fluid like supercritical helium. For low heat fluxes, heat transfer decreases with increasing heat flux because the thermal boundary layer is thickened by the expansion-driven velocity directed away from the heat transfer surface. For high heat fluxes, heat transfer increases with increasing heat flux because the thermal boundary layer thickness is reduced by the action of the expansion-driven axial velocity.
Two dimensional transient heat transfer in He II

   J.M. Pfotenhauer and X. Huang

Summary: A comparison is presented of transient heat flow in He II as measured experimentally and as predicted by analysis based on the Gorter-Mellink equation. The geometry is that envisioned for the He II cooling of a SMES (superconducting magnetic energy storage) system, namely, an annular layer of He II in direct contact with one layer of a solenoid and extending the full height of the coil. A normal zone over a fraction of a turn provides for two-dimensional heat flow in the annular layer of the He II. The comparison is given for both adiabatic and isothermal boundary conditions at the end of the channel. Good agreement between the analysis and the experimental data is found, verifying the usefulness of the analysis for large-scale systems. In addition, discrepancies between the analysis and data provide insight into the stability process of the He II cooled superconductor.
Pressure drop measurements on supercritical helium cooled cable in conduit conductors

   M.A. Daugherty, Y. Huang and S.W. Van Sciver

Summary: For extensive projects such as the International Thermonuclear Experimental Reactor design cooperation it is essential to know the pressure drops to be expected from different conductor geometries and operating conditions. To measure these drops a flow loop was constructed to circulate supercritical helium through different conductors. The loop is surrounded by a 5-K radiation shield to allow for stable operation at the required temperatures. A coil heat exchanger immersed in a helium bath is used to remove the heat generated by the pump. Pressure drops are measured across 1-m lengths of the conductors for various mass flow rates. Plots of friction factor versus Reynolds number are used to correlate the data. Supercritical helium flow through the two cable-in-conduit conductors tested in the 3 K to 7 K temperature range appears to undergo laminar to turbulent transition at Reynolds numbers varying from 1000 to 7000. It is concluded that flow area and cooled perimeter alone do not adequately correlate the observed pressure drop along the conductors.
Stability projections for high temperature superconductors

   H.L. Laquer, F.J. Edeskuty, W.V. Hassenzahl and S.L. Wipf

Summary: The stability of the high-temperature superconducting oxides has been analyzed, using the methodology developed for conventional type II superconductors. The results are presented in graphical form for the temperature range from 4 to 100 K. For a 90-K superconductor the first flux jump field peaks above 7 T at 60 K, and for a 120-K superconductor it peaks above 12 T at 75 K. The maximum adiabatically stable thickness increases greatly. The linear dimension of the minimum propagating zone increases by a factor of 3 to 5, and the quench propagation velocity drops by four orders of magnitude. It is concluded that the high-temperature superconducting materials will have much higher stability than conventional type II superconductors and that their high flux jump fields will make ultrafine multifilamentary conductors unnecessary and improve the outlook for tape conductors. The energy required to create a propagating zone is increased. However, methods of coil protection will have to be modified.
Quench detection of superconducting magnets using ultrasonic wave

   A. Ninomiya, K. Sakaniwa, H. Kado, T. Ishigohka and Y. Higo

Summary: An ultrasonic quench-detection method for superconducting magnets is presented. This nondestructive method monitors the change of the acoustic transfer function of a superconducting magnet induced by a local temperature rise or an epoxy crack. Experiments were carried out on a small epoxy-impregnated magnet. The experimental results show that a local temperature rise of about 2-3 K can be detected by this method. It is concluded that the technique can provide early quench warning by monitoring continuously the change of the acoustic transfer function of the magnet.
Instabilities of impregnated windings induced by epoxy cracking

   T. Yamashita, S. Nishijima, K. Takahata, T. Okada, T. Fukutsuka, K. Matsumoto and M. Hamada

Summary: Changes in the mechanical behaviour and the instabilities of impregnated windings induced by epoxy cracking have been studied in order to establish a methodology for constructing a superconducting magnet. Epoxy cracks are inevitably induced in the process of training. The cracks degrade the rigidity of the superconducting windings, hence the evaluation of epoxy cracks in impregnated windings is important in analyzing the stability of the windings. Test windings in which epoxy cracks were purposely introduced were used, and the degradation and the training behavior were measured before and after crack introduction. Before crack introduction the winding showed training, that is, the quench current increased with quench number. After crack introduction the quench current did not increase with quench number.
Stabilization of superconducting dry solenoids

   M. Urata and H. Maeda

Summary: Premature quenches in superconducting solenoids wound with Formvar-coated NbTi conductors have been studied. Some model coils wound with various tensions were tested. The experimental results are discussed with attention given to the stress distribution for coil winding, cool-down to liquid helium temperature, and energization at 4.2 K. Some mechanisms of premature quench are classified according to the winding tension, and some stabilization methods are presented on the basis of these quench mechanisms. It is found that if a solenoid is wound loosely, macroscopic slips occur in inner layers due to low frictional force. Although such motions are removed if the coil is wound tightly, shear stress concentration at the interface between the winding and the bore tube then causes quenches by microslips. Inserted polymer films affect the sliding behavior of the conductor, which can improve the coil performance.
High current density aluminium stabilized conductor concepts for space applications

   X. Huang, Y.M. Eyssa and M.A. Hilal

Summary: The authors report on a high-current-density aluminium-stabilized conductor concept for large spaceborne energy storage inductors. High-purity-aluminium-stabilized NbTi composite conductors cooled by 1.8-K helium can provide a winding current density up to 15 kA/cm/sup 2/ at fields up to 10 T. The conductors are edge-cooled with enough surface area to provide recovery following a normalizing disturbance. The conductors are designed so that current diffusion time in the high-purity aluminium is smaller than the thermal diffusion time in helium. Conductor design, stability, and current diffusion are considered. The numerical analysis of transient stability shows that aluminium-stabilized conductors with final resistivity ratio greater than 800 can be stable in a 1.8-K pressurized helium II bath up to 50 kA (J=15 kA/cm/sup 2/) at fields up to 10 T. single-layer toroids are preferred over multilayer ones because of their simplicity of construction, large current requirement, and better magnetoresistance.
Effects of insulation on potted superconducting coils

   A.F. Zeller, J.C. DeKamp, C.T. Magsig, J.A. Nolen and A.D. McInturff

Summary: The authors studied the effects of the insulation on potted superconducting coils wet-wound with Stycast 2850 FT epoxy. The wire was insulated with one or two insulating varnishes: Formvar (a polyvinyl formal resin) or Polyesterimid (a phenolic resin). Although differences in maximum currents were observed, it was found that the type of insulation did not affect the training behavior.
Quenching of multisection superconducting magnets and internal and external shunt resistors

   A.A. Konjukhov, V.A. Malginov, V.V. Matokhin and V.R. Karasik

Summary: Self-protection of superconducting magnets by subdivision using internal and external shunt resistors was investigated. Temperature rise at various points of the winding was measured by means of thermocouples soldered to the conductor. The velocity of the normal-zone propagation along radial and axial directions was obtained. Initial current was varied from 0.3 to 0.9I/sub q/=1000 A. The effectiveness of protection by subdivision with external shunts depended on the number and dimensions of sections. It increased with decreasing single section size. When placed in the magnet, shunts work as a heater and diminish the quenching time and maximum winding temperature.
Protection of superconducting magnets with high current density

   V.R. Karasik, A.I. Rusinov, V.S. Vysotsky and A.A. Konujkhov

Summary: The effectiveness of superconducting-magnet protection by subdivision is demonstrated. An analytical model of quenching is proposed which is consistent with experimental results and makes it possible to estimate maximum temperature and voltage, the correct volume of a single section, and other parameters of protected winding. It is shown that subdivision decreases overheating and transient voltage in the winding.
Study of quench propagation velocity in superconducting magnets for UNK

   I.V. Bogdanov, P.A. Shcherbakov, V.P. Snitko, N.P. Tkachenko, L.M. Vasiliev, M.G. Vybornov and A.V. Zlobin

Summary: Two superconducting magnet models, warm-iron and cold-iron designs, are studied. The authors describe a method for measuring quench propagation velocity in superconducting cables with a transport current in an external field under cooling conditions typical for those of the magnet winding. Results on measuring quench propagation velocities in warm-iron and cold-iron designs are presented, and the results obtained for short samples and model coils are compared. They make it possible to simulate numerically a quench process in the coil.
Magnets for 150 GHz gyrotrons

   W. Maurer, B. Piosczyk, M. Forster, D. Krischel and H. Peschel

Summary: The development of three magnet sets for a 150-GHz gyrotron is described. This development has the ultimate goal of producing a 150-GHz gyrotron unit with 1-MW power in steady-state operation for plasma heating. The design criteria and the problems and difficulties during development phase are discussed. The first set, consisting of normal-conducting and superconducting solenoids and normal-conducting steering coils, showed problems during operation. The second magnet set, with only two normal-conducting magnets in the emitter zone, is working without any problems. The third set, (in the construction phase), is all superconducting. Using the second set an output RF power of 200 kW was achieved for a few milliseconds.
Impact of high temperature superconductors on the possibility of radio-frequency confinement

   S.O. Dean

Summary: It is suggested that recent high-temperature superconductors may impact the feasibility of RF confinement in two important ways: higher-temperature superconductors should have higher critical B fields and consequently may allow higher critical B fields to be sustained in the cavity, thus allowing the necessary confining pressure to be achieved; and the higher-temperature superconductors lower the refrigeration power necessary to maintain the superconducting cavity, thus allowing a favorable energy balance. Issues discussed include the frequency condition and the pressure balance, the maintenance of a superconductor near a thermonuclear plasma, and the field configuration. It is concluded that the old bases for rejecting the possibility of RF confinement of thermonuclear plasma are no longer valid.
Standard-II and extended tests of the Swiss LCT-coil

   J.A. Zichy, B. Jakob, K. Kwasnitza, C. Sborchia, G. Vecsey, M.S. Lubell and S.S. Shen

Summary: The Swiss contribution to the international Large Coil Task was a D-shaped 2.5-m*3.5-m-bore, superconducting toroidal field coil of 8 T. The conductor was made from copper-stabilized, fully transposed NbTi filaments, cabled in three stages and cooled with pressurized supercritical helium. The testing of the six coils was successfully finished last year at Oak Ridge National Laboratory. The AC loss measurement data taken during the standard-II tests are presented. The results are compared with predictions made while designing the coil. The results of the extended-condition tests are discussed. Recently analyzed quench data, taken during the entire test period, are presented. The data showed that a fully transposed filamentary conductor with short twist pitch and well-designed resistive barriers reduces substantially the AC losses in the windings. The overall current density reached 33 A/mm/sup 2/ at 8.96 T and 29.6 T/mm/sup 2/ at 9.1 T in the high- and maximum-field torus tests, respectively. This demonstrated that the NbTi-based CH conductor had a sufficient current margin.
Advanced superconducting MHD magnet design for a retrofit power plant

   P.G. Marston, J.R. Hale and A.M. Dawson

Summary: A magnet has been designed for an MHD (magnetohydrodynamic) topping cycle retrofit of a conventional power plant. The channel power output will be approximately 35 MWe. The magnet which will have 4.5-T peak on-axis field, will be constructed of an unusual NbTi superconductor wound into four subunits per dipole half. These will consist of three 45 degrees saddle coils with circular or ellipsoidal end turns and a single planar coil with a modified racetrack shape that will serve principally as a field-shaping coil. This planar coil also allows a substantial reduction in the ratio of peak to central field strength. Among the unique features of this design will be the use of flexible bands in tension as the primary element of the transverse force containment structure. The conductor will be of the cable-in-conduit type with a cable having a low copper-to-superconductor ratio and a thick-walled aluminum conduit sheath. The sheath will support the axial loads on the saddles and will also provide thermal mass for protection against overheating in the event of an energy dump. The analysis and design of this magnet system and its projected advantages in both performance and economics are discussed.
Comparison of two ICCS conductors for MHD application

   J.R. Hale, P.G. Marston and A.M. Dawson

Summary: Two subscale, internally cooled, cabled superconductors (ICCSs) have been examined as candidates for use in a retrofit MHD (magnetohydrodynamic) topping cycle magnet. One of these was a 3*3*3 cable in which all the strands were multifilamentary NbTi stabilized with copper. The other was a 3*3*3 cable in which two strands in each of the nine triplets wa OFHC copper and one was multifilamentary NbTi. The overall copper-to-superconductor ratio for each of the two 27-strand cables was approximately the same. The two conductors were cowound onto a grooved mandrel in such a way that they could be tested alternately. Each sample was instrumented with a heater at the center of the conductor length and with a pressure transducer, four pairs of voltage taps, and one iron-doped gold/constantan thermocouple. Performance tests of the conductors were made at 6-, 7-, and 7.8-T background magnetic fields and at heater input energies ranging from 60 mJ/cm/sup 3/ to 1758 mJ/cm/sup 3/ of conductor. The results of these tests and their significance for MHD magnet design and economics are discussed.
An overview of the SMES ETM program: the Bechtel team's perspective

   R.J. Loyd, T.E. Walsh, E.R. Kimmy and B.E. Dick

Summary: Phase I of the conceptual design and component development for the SMES/ETM (Superconducting Magnetic Energy Storage/Engineering Test Model) program is discussed. The approach chosen is to develop and test all key components at full scale; in particular, the selected operating current for the conductor is 200 kA. The ETM is supposed to deliver from 400 to 1000 MW for 100 s and from 10 to 20 MW for 2 to 3 h. The lower end of each range was chosen for the design described. The result is a 21-MWh coil discharging 56% of its energy at 400 MW in 100 s or discharging 95% of its energy at 10 MW over 2 h. The design philosophy is discussed.
Current diffusion effects on the performance of large monolithic conductors

   C.A. Luongo, R.J. Loyd and C.L. Chang

Summary: Describes a mathematical model developed to study the effects of slow current diffusion on the performance of large monolithic conductors. The model is based on the numerical solution of the coupled heat and magnetic flux (current) diffusion equations in slab geometry. It is used to calculate stability margins for large monoliths; relatively low margins are predicted. Normal-zone propagation velocities are also calculated. It is shown that for large monolithic conductors with long current diffusion times a propagating normal zone can be established even in a conductor designed under the traditional cryostability criterion. Examples are given to illustrate the fact that for large monoliths cryostability must be assigned a new meaning (or lack of). The results are pertinent to the development of full-scale superconducting magnetic energy storage.
AC losses in the SMES conductor and coil structure

   H. Gurol, L. Motowidlo and C. Luongo

Summary: The authors present a methodology for calculating AC losses in the SMES/ETM (Superconducting Magnetic Energy Storage/Engineering Test Model) conductor and coil structure. Coupling and eddy current losses are discussed for a 100-s discharge of a 143-m-diameter ETM with a total stored energy of 21 MWh. The chosen pitch length, filament size, and winding configuration are shown to result in coupling losses that are small during this 400-MW. The total coupling losses are about 0.0048 J/cm/sup 3/. The structural current losses result in energy deposition of about 0.05 J/cm/sup 3/ during the same discharge. The energy is being deposited in the structure (away from the conductor) and over a very long time as far as stability is concerned (100/s). In addition, the highest power deposition occurs toward the end of the discharge, when the conductor current is lowest. The AC losses during slow utility discharge, calculated using the proposed methodology, represent part of the steady-state heat load to be removed by the refrigeration system.
SMES conductor test program

   J. Colvin, F.R. Huson, P. Pissanetzky, R. Rocha, W. Schmidt, G. Shotzman, D. Stanko, J. Zeigler, P. VanderArend and J. Purcell

Summary: Phase I of the Superconducting Magnetic Energy Storage/Engineering Test Model (SMES/ETM) project includes a test program to evaluate superconductors under development. Key aspects of this program are presented including the operation of the high test facility at 1.8 K. Descriptions are given of the 1.8-K refrigeration, the background field, the current supply, and the test setup.
Thermal-hydraulic simulation of helium expulsion from a cable-in-conduit conductor

   C.A. Luongo, R.J. Loyd, F.K. Chen and S.D. Peck

Summary: The authors present simulation results for a quenching cable-in-conduit conductor (CICC) for application in superconducting magnetic energy storage (SMES). The details of the model and its computational implementation (the code HEDUMP) are discussed. An extensive verification process shows that HEDUMP can accurately model a quenching CICC. Preliminary results of the simulation are given and discussed. In particular, the normal zone propagation is studied. It is shown that CICCs exhibit a thermohydraulic quench-back behavior whereby superconducting regions ahead of the normals front are suddenly driven normal by frictional dissipation and/or compression heating of the fluid.
SMES conductor design

   D.L. Walker, F.M. Kimball, E.R. Kimmy, S.D. Peck, H.H. van den Bergh, R.J. Loyd and C.A. Luongo

Summary: The authors report the current status of the 200-kA SMES (superconducting magnetic energy storage) conductor design and the future test and development plans. The basis is given for selecting the design criteria for each requirement used in the conductor tradeoff study. A CICC (cable-in-conduit conductor) concept has been selected for the SMES system because it represents the most appropriate route for current scale-up to 200 kA (or more) as required by SMES. A CICC has a high stability margin, utilizes proven manufacturing processes, eliminates the need for a high-risk helium vessel and complex helium dump system, and is cost-effective. The results of thermal and stress analyses are given for stability and thermal and magnetic loadings. Finally, a preliminary manufacturing plan is described.
Design for a superconductive power cable for SMES

   Q. Xiuying, R.L. Kustom and J.J. Skiles

Summary: Superconductive power cables are considered for use as the busbar between a 5500-MWh superconductive magnetic energy storage (SMES) coil and the power-conditioning circuits. The busbar is configured to minimize forces due to the magnetic field. Three design options for the superconducting cable are presented. The peak operating current is 230 kA. Room-temperature copper cable is connected in parallel to the superconductive cable for redundant operation in the event of loss of cooling of the superconductor. Calculations of temperature rise versus time without cooling are presented.
Self protection of high current density superconducting magnets

   M.A. Hilal and Y.M. Eyssa

Summary: Two schemes are proposed for superconducting magnet protection. The first is a self-protection scheme for high-current-density conductors using a metallic structure such as beryllium to act as a transformer secondary, with the conductor winding acting as the primary. A dump resistor is proposed as the second protection scheme for comparison. It requires the use of a lightweight high-temperature dump resistor with the current density limited to 15 kA cm/sup 2/. The self-protection scheme is being developed for spaceborne and mobile magnet systems.
A unique cabling machine designed to produce Rutherford-type superconducting cable for the SSC project

   J. Grisel, J.M. Royet, R.M. Scanlan and R. Armer

Summary: Up to 25000 km of keystoned flat cable must be produced for the SCC (Superconducting Super Collider) project. Starting from a specification developed by Lawrence Berkeley Laboratory, a special cabling machine has been designed to run at a speed corresponding to a maximum production rate of 10 m/min. This cabling machine is the key part of the production line, which consists of a precision Turkshead equipped with a variable power drive, a caterpillar, a dimensional control bench, a data acquisition system, and a take-up unit. The main features of the cabling unit described are a design with nearly equal path between spool and assembling point for all the wires and the possibility of running the machine with several over- or under-twisting ratios between cable and wires. These requirements led to the choice of an unconventional mechanical concept. With this equipment, the first trial run using 30 strands of superconducting wire produced cable within the dimensional tolerances at speeds up to 10 m/min without any crossovers.
An alternate method for designing dipole magnet ends

   W.L. Pope, M.A. Green, C. Peters, S. Caspi and C.E. Taylor

Summary: The authors present a novel procedure for designing dipole magnet ends which can be applied to magnets with either cylindrical or conical bulged ends to produce integrated field multipoles which meet the constraints imposed by the SSC (Superconducting Super Collider) lattice. The method makes it possible to couple existing multiparameters optimization routines (i.e. MINUIT with suitable independent parameter constraints) with a computer code DIPEND, which describes the multiples, so that any reasonable objective (i.e. minimizing integrated sextupole and decapole) can be met. The authors describe how the computer method was used to analyze the bulged conical ends for an SSC dipole.
Superconducting Super Collider second generation dipole magnet cryostat design

   R.C. Niemann, R.C. Bossert, J.A. Carson, N.H. Engler, J.D. Gonczy, E.T. Larson, T.H. Nicol and T. Ohmori

Summary: The second-generation cryostat design for the Superconducting Super Collider has been developed utilizing the experiences gained during the construction, installation and operation of several full-length first-generation dipole magnet models. The nature of the cryostat improvements is described. Considered are the connections between the magnet cold mass and its supports, cryogenic supports, cold mass axial anchor, thermal shields, insulation, vacuum vessel, and interconnections. The details of the improvements are enumerated and the results of available component and system evaluations are presented.
SSC detector solenoid

   R.W. Fast, J.H. Grimson, R.D. Kephart, H.J. Krebs, M.E. Stone, E.D. Theriot and R.H. Wands

Summary: A detector utilizing a superconducting solenoid is being discussed for the Superconducting Super Collider (SSC). A useful field volume of 8-m diameter*16-m length at 1.5-2 T ( approximately 1 GJ at 2 T) is required. It has been decided that all of the particle physics calorimetry will be inside the bore of the solenoid and that there is no need for the coil and cryostat to be thin in radiation lengths. An iron yoke will reduce the excitation required and will provide muon identification and a redundant momentum measurement of the muons. A conceptual design was developed to meet these requirements. The magnet will use a copper-stabilized Nb-Ti conductor sized for a cryostable pool boiling heat flux of approximately 0.025 W/cm/sup 2/. The operating current, current density, coil subdivision, and dump resistor have been chosen to guarantee that the coil will be undamaged should a quench occur. The 5000 metric tons of calorimetry will be supported from the iron yoke through a trussed cylindrical shell structure separate from the cryostat. The coil and case, radiation shield, and stainless vacuum vessel would be fabricated and cryogenically tested as two 8-m sections.
Integrated thermal analysis of the production dipole magnets for the superconducting super collider

   G.E. Hardy and S.D. Peck

Summary: A thermal model of a 16.6-m-long Superconducting Super Collider dipole cryostat was developed to evaluate the system thermal behavior of the dipoles. The model incorporates in detail all the heat flow paths in the cryostat with the capacity to model all steady-state and transient thermal boundary conditions to which the cryostat is subjected during normal and upset conditions. The model predicts heat leaks to the cryogenics of 25.4 W per dipole to 80 K, 2.64 W per dipole to 20 K, and 0.174 W per dipole to 4.35 K during normal operation, which compare favorably to the established heat leak budgets. The model shows that the synchrotron radiation does not raise the temperature of the winding more than 0.2 K relative to the inlet temperature of the helium. Cooldown from room temperature to 55 K is shown to take from 1.5 to 3 h with flow rates of the order of 100-200 g/s. Warmup to room temperature from steady-state operating conditions takes approximately 17.5 h using 5-kW heaters. Recooling of the winding following a quench takes about 3.5 min from 70 K and 9 min from 300 K.
Design study on future accelerator magnets using largely keystoned cables

   K. Ishibashi, K. Kamezawa, A. Katase, A. Terashima, Y. Sakakibara, Y. Funahashi and H. Hirabayashi

Summary: In the near future, superconducting magnets with a small beam aperture will be required for high-energy proton colliders. When coils are designed to be self-arched over a small beam pipe, the magnet construction is simplified both in the winding procedure and in the field quality control. Fabrication of these coils requires cables with large keystone angles. A braid-in-strand structure was devised to produce these cables. Two types of self-arched coils were found to produce good field homogeneity. Prior to construction of a whole magnet, a straight section of a circular-aperture magnet was fabricated to obtain detailed information on the cable position. Strand positions have been measured on the cross section of the coil. Magnetic field analysis is made on the basis of the position of the strands.
The first, industry made, model magnet for the CERN Large Hadron Collider

   R. Perin, D. Leroy and G. Spigo

Summary: The first magnet model for the LHC (Large Hadron Collider) is a single-aperture, 1-m-long, dipole magnet based on NbTi cable technology and designed for an 8-T nominal field at 2 K. It reached and passed its nominal field without any quench and attained 9.1 T, where it operated without quenching before the first campaign of tests was voluntarily stopped. In a second test campaign a 9.3 T central field was attained. After a description of the magnet, the authors discuss the cable characteristics, manufacturing tools, and magnet performance.
Towards a 1 m high field Nb/sub 3/Sn dipole magnet of the ELIN-CERN collaboration for the LHC-project-development and technological aspects

   S. Wenger, F. Zerobin and A. Asner

Summary: The main design features of the 1-m-long Nb/sub 3/Sn superconducting dipole model for the Large Hadron Collider (LHC) are presented. The magnets are designed to operate at 4.2 K with a nominal field of about 9-10 T. After describing the general design of the model magnet, the authors discuss electrical and mechanical computations, short-model tests, cable tests, and coil-winding experience.
Optimization of multiwire coil ends having 45 degree bends

   G.H. Morgan

Summary: Multiwire is the name of a proprietary process for affixing small-diameter wires to a flat substrate using digitally controlled machinery. It is currently being used to wind trim coils for the SSC (Superconducting Super Collider) dipoles on a flexible substrate which is wrapped around the beam tube. The current multiwire process does not permit a change in direction of the wire other than 45 degrees . The author investigates the location of 45 degrees bends in the flattened coil along straight lines in such a way as to eliminate or reduce higher harmonics in the ends.
Time variations of fields in superconducting magnets and their effects on accelerators

   D.A. Herrup, M.J. Syphers, D.E. Johnson, R.P. Johnson, A.V. Tollestrup, R.W. Hanft, B.C. Brown, M.J. Lamm, M. Kuchnir and A.D. McInturff

Summary: The time dependence of magnetic fields in the superconducting magnets of the Fermilab Tevatron is discussed. A field variation of order 1 G at the aperture radius is observed. Studies on both full-sized Tevatron dipoles and prototype magnets have been used to elucidate these effects. Explanations based on eddy currents in the coil matrix or on flux creep in the superconducting filaments are explored with these tests. Measurement results and techniques for controlling the effect based on novel laboratory tests and the latest accelerator operation are presented. It is shown that small but important changes in the fields occur with (ln t) time dependencies. For accelerator operation, in both laboratory and accelerator measurements, some events which might be associated with nonsmooth behavior (sudden changes on the relevant time scale) and with deviations at long times from observed (ln t) behavior have been seen.
Studies of time dependence of fields in Tevatron superconducting dipole magnets

   R.W. Hanft, B.C. Brown, D.A. Herrup, M.J. Lamm, A.D. McInturff and M.J. Syphers

Summary: The time variation in the magnetic field of a model Tevatron dipole magnet at constant excitation current has been studied. Variations in symmetry allowed harmonic components over long time ranges show a log t behavior indicative of 'flux creep'. Both short-time-range and long-time-range behavior depend on the excitation history. Similar effects are seen in the remnant fields present in full-scale Tevatron dipoles following current ramping. Both magnitudes and time dependences are observed to depend on details such as ramp rate, flattop duration, and number of ramps. In a few magnets, variations are also seen in symmetry-disallowed harmonics.
Experience during series production of the superconducting HERA dipole magnets

   C.-H. Dustmann, M. Forster and D. Bonmann

Summary: A production flow chart for the series production of the superconducting HERA dipoles at a rate of one magnet per day is presented. Some of the major problems which occurred during the series production of the HERA magnets and their solution are discussed. Experience obtained with collared coil production, coil sizes, and quench heaters is outlined.
Manufacture and testing of 465 km superconducting cable for the HERA dipole magnets

   R.K. Maix, D. Salathe, S.L. Wipf and M. Garber

Summary: Experience with strand and cable manufacturing are presented together with mechanical and electrical data. A comparison of the critical currents of the cables with the sum of the critical currents of the 24 individual strands before cabling shows that with the usual definition the cables have practically no degradation. Finally, it is shown how different cable compactions and an additional calibration run through the cabling machine influence the critical current.
First industry made superconducting quadrupoles for HERA

   R. Auzolle, J. Perot, J.M. Rifflet, A. Fokken, O. Peters and S. Wolff

Summary: 246 superconducting quadrupoles of ten different kinds have to be built for the HERA proton machine at DESY, Hamburg, West Germany. After several prototypes were made and tested in the SACLAY laboratory the mass fabrication was committed to industry. Three different European firms have been selected to build both the magnets and their cryostats. The technology transfer from laboratory to industry, the fabrication control, and the results on the first magnets made are described.
Prototype thin superconducting solenoid for particle astrophysics in space

   T. Mito, A. Yamamoto, Y. Makida, T. Haruyama, H. Inoue, N. Kimura, N. Minowa, H. Yamaoka and Y. Doi

Summary: A description is given of a prototype magnet which is a very thin and lightweight superconducting solenoid 1 m in diameter, 1.3 m in length and with a 1.27 T central field. The authors plan to use this device in balloon experiments scheduled for 1990 to measure high-energy cosmic rays as preliminaries to the experiment in space. They have constructed the model magnet, which is the same size as the prototype magnet and has 1/4 superconducting wire and 3/4 dummy wire. The cooling, exciting, and quench properties of this magnet were measured and compared with design values to verify the coil winding technique and the static indirect cooling method using pure aluminum.
Design of a large superconducting spectrometer magnet

   T. Shintomi, O. Hashimoto, Y. Makida, T. Mito, T. Nagae and Y. Yamanoi

Summary: A superconducting spectrometer magnet for nuclear physics experiments is currently under construction. The magnet has a sector-type coil. The magnetic field is 3 T with a magnet gap of 50 cm, and the stored energy is 11.8 MJ. Ease of operation and maintenance are taken into consideration in the design. Three-dimensional magnetic field calculations and the stress analysis have been performed. The code QUENCH was applied to determine the operating current and check coil safety. A current of 500 A was selected. Heat leaks were checked and estimated to be <2 W at 4 K. A small refrigerator is to be used for thermal insulations at 80 and 20 K.
Magnetic structure for a superconducting variable frequency electron cyclotron resonance ion source

   T.A. Antaya, A.F. Zeller, J.M. Moskalik, H.G. Blosser, J.A. Nolen and K.A. Harrison

Summary: Electron cyclotron resonance (ECR) ion source are, at present, the leading source of highly charged DC beams of positive ions. Fully stripped light ions through argon have been obtained, and ionization levels of 25-35 electrons removed have been obtained for heavy mass species. Major applications of ECR ion sources for highly charged ions now include approximately 30 nuclear, atomic, and high-energy physics laboratories worldwide.
A 17 T NbTi-Nb/sub 3/Sn superconducting magnet with low-purity holmium core

   L.Z. Lin, K.W. Li, C.Y. Lin, S. Han, X.S. Li and L.G. Yan

Summary: A 14-T NbTi-Nb/sub 3/Sn superconducting magnet system with 31-mm bore has been constructed and tested. The magnet system consists of three coils one of NbTi and two of Nb/sub 3/Sn. Two different cross sections of Nb/sub 3/Sn wire constructed using the bronze method were chosen for the outer Nb/sub 3/Sn coil of 80-mm bore, and an (NbTi)/sub 3/Sn wire made by the high-tin-content Nb tube method was used to build the inner Nb/sub 3/Sn coil. The NbTi-Nb/sub 3/ magnet system has successfully achieved a 14.42 T central field at 4.2 K. To obtain a higher magnetic field, a pair of low-purity holmium cores of 25-mm diameter were used. The test of the NbTi-Nb/sub 3/Sn magnet with the holmium cores shows that the central field increases from 14 T to 17 T at 4.2 K.
The optimization of NbTi-Nb/sub 3/Sn high field superconducting magnet used for physics experiments

   B. Han, S. Han and Z.X. Feng

Summary: An approach to optimum-cost design of a multigraded NbTi-Nb/sub 3/Sn high-field superconducting magnet is proposed. Investigation shows that by reasonable choice of the contribution of NbTi and Nb/sub 3/Sn coils to the central field and by properly increasing the beta of both, an optimum-cost design of the NbTi-Nb/sub 3/Sn solenoid magnet can be obtained. As an example, a calculation of a 14-T three-graded NbTi-Nb/sub 3/Sn superconducting magnet with a bore of 31-mm diameter is given.
Design and model tests of a 7.5 T wiggler for the Max-Lab synchrotron radiation facility

   J.-T. Eriksson, L. Kettunen, R. Mikkonen and L. Soderlund

Summary: A three-pole superconducting wiggler magnet has been designed to provide a peak flux density of 7.5 T. Two-dimensional software was used for narrowing down size parameters and a 3-D program was used for calculating the end fields. The design criteria were maximum peak flux density at minimum overall length and minimum helium boil-off. A 2/3-scale model magnet has been built and tested in order to gain information about the three-pole concept. Experimental verification of the calculated flux densities along the beam track has been obtained.
Construction of optimized superconducting spin precession magnets for neutron spectroscopy

   H.H.J. ten Kate, R.A. Hartmann, C.M.E. Zeyen, B. ten Haken and L.J.M. van de Klundert

Summary: The design and construction of a superconducting magnet system for a high-resolution neutron spin echo spectrometer. The principal solution for the field shape of optimal precession magnets is B/sub 0/cos/sup 2/( pi z/L). In practical precession magnets, this field shape is approximated by 30 superimposed concentric solenoids with a bore of 80 mm. The required field integral of 1 Tm, providing 10/sup 4/ precession turns, is achieved in a magnet with a length of about 1.5 m. The field in the center is 1.5 T maximum. The relative line integral inhomogeneity of about 10/sup -3/ obtained with such a coil is improved to less than 10/sup -6/ by two in-beam correction coils. The advanced homogeneity level means that after 10000 precession turns the precession angle remains still well defined without using tedious correction procedures.
Some aspects of modern theory of applied superconductivity

   N.N. Martovetsky

Summary: Insight into applied superconductivity (SC) based on C.P. Bean's model (1964) of critical state concerning processes which take place in the SC wires is used to develop a series of recommendations for superconductor advances. There are many principal facts from experiments and practice which can not be explained within the framework of this understand, especially for nonstabilized conductors with high currents. This contradiction originates from the fact that a transition characteristic of a superconductor is smoothed in a region of electrical fields where modern superconductors work. This fact required revision of many aspects of the theory and practice of applied superconductivity. A review of the main results which have been obtained is presented. The possibility of stable performance of SC composites with high currents and poor cooling with various types of disturbances is given.
General formulas for the adiabatic propagation velocity of the normal zone

   A. Devred

Summary: The influence on the propagation velocity of the normal zone of four phenomena was investigated: (1) the temperature dependence of the specific heat and the thermal conductivity; (2) the current-sharing zone; (3) the electromagnetic diffusion of current through a possible superstabilizer; and (4) the thermal diffusion through a possible insulator. At the beginning, these influences were studied independently of each other. In all cases, after a model of the particular phenomenon was created, the equations of thermal and electromagnetic behavior were solved analytically and the expressions for the propagation velocity obtained. These expressions were then put into nondimensional forms, which have allowed four correction factors to be defined that take into account the influences studied, and depend only on one or two nondimensional parameters. Subsequent studies were made to investigate how to combine these correction factors to obtain general formulas for the velocity, taking into account a part or all of these influences. A review is presented of these formulas, which are of interest for the superconducting windings where the heat transfer to helium can be neglected on the time scale of the quench process.
Designing for superconducting magnet stability using minimum propagating zone theory

   P.W. Eckels

Summary: Minimum propagating zone (MPZ) theory has been applied to the design of several superconducting coils which were, at the time of their conceptualization, novel and unique concepts. Each of the coils, the 300-kJ pulsed discharge coil, the Nb/sub 3/Sn forced flow-cooled Large Coil, and an epoxy potted coil, utilized a form of the MPZ theory to relate a different type of cooling and structural support system to the chosen magnet stability criterion. The design philosophy, analysis, and performance of the magnets are reviewed, and correlation of the quench conditions with conductor diameter is clearly indicated. The MPZ concept is shown to be a powerful tool, and it has had a major impact on the design parameters and operating modes of these coils.
Quench pressure, thermal expulsion, and normal zone propagation in internally cooled superconductors

   L. Dresner

Summary: When a nonrecovering normal zone appears in an internally cooled superconductor, the pressure in the conductor rises, helium is expelled from its ends, and the normal zone grows in size. A model of these processes is presented that allows calculation of the pressure, the expulsion velocity, and the propagation velocity with simple formulas. The model is intended to apply to conductors such as the cable-in-conduit conductor of the Westinghouse LCT (Large Coil Task) coil, the helium volumes of which have very large length-to-diameter ratios (3*10/sup 5/). The predictions of the model agree with the rather limited data available from propagation experiments carried out on the coil.
Quantification of disturbance energy due to conductor motion and stability analysis of superconducting composite wire

   O. Tsukamoto, T. Takao and S. Honjo

Summary: The authors propose a model to quantify the disturbance energy due to conductor motion. The model relates the disturbance energy to mechanical properties of the conductor, electromagnetic force, and winding structure. The stability of a superconducting composite conductor subject to an abrupt conductor motion is analyzed on the basis of the proposed model. It is pointed out that the stability of the conductor is improved by decreasing the distance between spacers placed between the conductors. However, it is pointed out that there is a limit to the improvement, because of limited accuracies of the conductor and spacer dimensions.
Influence of dump voltage and allowable temperature rise on stabilizer requirements in superconducting coils

   S.W. Schwenterly

Summary: The authors present some simple relations between the dump voltage and the stored energy, temperature rise, and coil geometry that are useful in scoping the required amount of stabilizer. Comparison with some recently proposed fusion magnet system designs indicate that excessive dump voltages could result in some cases. High-temperature superconductors may require more stabilizer than the conventional alloys. Calculations with simple model coil systems indicate how tradeoffs between between various coil parameters affect the dump voltage.
Development of a forced-cooled superconducting coil with high average current density (DPC-TJ)

   T. Hamajima, A. Tanaka, H. Shiraki, M. Shibui, Y. Sanada, M. Naganuma, M. Shimada, T. Fujioka, M. Nishi, H. Nakajima, K. Koizumi, Y. Takahashi, T. Ando, H. Tsuji and S. Shimamoto

Summary: A forced-cooled superconducting coil (DPC-TJ) using a double-walled cable-in-conduit, the so-called Performed Armor CICC, has been developed. The DPC-TJ is an advanced coil with an average current density of 40 A/mm/sup 2/, operating current of 24 kA, and field of 12 T. The DPC-TJ coil has several advantages such as mechanical rigidity, negligible degradation of critical current, sound electrical insulation, and excellent winding tolerance compared with a conventional forced-cooled coil. A superconducting strand was developed with the aim of improving the critical current density and resistivity. The resulting Nb-tube-processed (NbTi)/sub 3/Sn strand fulfils the requirement that the critical current density be more than 600 A/mm/sup 2/ at 12 T and the RRR (residual resistivity ratio) be higher than 50.
Structural characteristics of proposed ITER TF coil conductor

   C.R. Gibson and J.R. Miller

Summary: An analysis has been conducted of the effect of transverse loading on a cable-in-conduit conductor which has been proposed for the toroidal field coils of the International Thermonuclear Experiment Reactor. The primary components of this conductor are a loose cable of superconducting wires, a thin-wall tube for helium containment, and a U-shaped structural channel. A method is given where the geometry of this conductor can be optimized for a given set of operating conditions. It is shown, using finite-element modeling, that the structural channel is effective in supporting loads due to transverse forces and internal pressure. In addition, it is shown that the superconducting cable is effectively shielded from external transverse loads that might otherwise degrade its current-carrying capacity.
Detailed distribution of AC loss in the NET TF coils

   L. Bottura and J. Minervini

Summary: The AC loss in the NET (Next European Torus) TF (toroidal field) coil has been computed as a function of space and time using a field map of the DC toroidal field components and AC poloidal field components for three proposed conductor designs. Resolving the field B, field change Delta B, and field derivative dB/dt into components transversal and parallel to the conductors, the value of the coupling, eddy currents, and hysteresis losses was computed using a set of simplified expressions. The calculation performed on the whole coil is presented, using the distributions along a developed pancake of the instantaneous and average values of AC loss.
Large Coil Task instrumentation and diagnostics-a review

   J.W. Lue, J.F. Ellis, W.A. Fietz, M.S. Lubell, J.N. Luton, S.W. Schwenterly, C.T. Wilson and R.E. Winterberg

Summary: The goal of the Large Coil Task (LCT) was to develop large toroidal superconducting magnets for fusion reactors. Each of the six coils built for this task was heavily instrumented with some 200 to 400 sensors and diagnostic voltage taps to test its performance and characteristics. In addition, more than a thousand sensors were installed in the facility and test-stand components to ensure safe and controlled operation. A review is presented of the various types of thermometers, pressure transducers, flowmeters, strain gages, displacement transducers, acoustic emission sensors, field probes, and other diagnostic instrumentation used in the LCT. The usefulness of the sensors, the difficulties with some of them, and the reliability of different groups of sensors in this task are described.
Progress in the manufacture of the US-DPC test coil

   M.O. Hoenig, M. Takayasu, R.N. Randall, J.E. Tracey, J.R. Hale, M.M. Morra, I. Hwang and P. Marti

Summary: A superconducting ohmic heating coil is being built by MIT to be tested in early 1990 at the Japan Atomic Energy Research Institute (JAERI). This 2-m-diameter coil will be wound from Nb/sub 3/Sn cable-in-conduit conductor. The coil and conductor are briefly described. Manufacturing procedures and problems encountered in the fabrication of the conductor up to August 1988 are considered. Included are descriptions of wire chrome plating, cable manufacture, and conduit fabrication.
Current leads with high T/sub c/ superconducting bus bars

   A. Matrone, G. Rosatelli and R. Vaccarone

Summary: The feasibility of combined current leads with a superconducting extension using high-T/sub c/ superconductors is demonstrated. The performance of systems with heatsink at room temperature or at LN/sub 2/ temperature are compared. In both cases the leads and the busbars are cooled by counterflowing helium gas and the superconducting part can be, depending on T and I, in the superconducting state, in the normal state, or in the current-sharing regime. The improvement obtained by such a system is important notwithstanding the limited current capacity of today high-T/sub c/ superconductors, at least for the LN/sub 2/-cooled system.
Superconducting cyclotron for medical application

   H. Blosser, J. Bailey, R. Burleigh, D. Johnson, E. Kashy, T. Kuo, F. Marti, J. Vincent, A. Zeller, E. Blosser, G. Blosser, R. Maughan, W. Powers and J. Wagner

Summary: A medical superconducting cyclotron, the first such project to be undertaken, is under construction. The cyclotron will be used to produce neutron beams for use in radiation treatment of cancer. The purpose of such treatment is to administer lethal doses of radiation to tumor cells while minimizing dose to normal tissue; rather intense neutron beams are required for the treatments to occur in a reasonably expeditious time and the device needs to be able to fire the neutrons at the patient from any angle. The authors briefly review the medical rationale for such a device and then describe the cyclotron design with special emphasis on details of the superconducting coil and cryostat.
Superconducting magnets for whole body magnetic resonance imaging

   M.F. Murphy

Summary: Superconducting magnets have achieved preeminence in the magnetic resonance imaging (MRI) industry. Further growth in this market will depend on reducing system costs, extending medical applications, and easing the present siting problem. Novel magnet designs are described that address these issues. Compact magnets are economical to build and operate. Two 4-T whole-body magnets for research in magnetic resonance spectroscopy (MRS) are now in operation. Active-shield magnets, by greatly reducing the magnetic fringe fields, will allow MRI systems with superconducting magnets to be located in previously inaccessible sites.
A 5 Telsa imaging magnet for imaging laboratory animals

   J.L. Carolan, W.A. Burns and M.A. Green

Summary: A report is presented on the construction of the first of a series of magnetic resonance imaging (MRI) imaging magnets for laboratory animals. The magnet has a 33-cm warm bore with a design central induction of 5.5 T without active shielding and 5.0 T with active shielding. The magnet will be used for both imaging and spectroscopy of living animals. The active shield system is designed so that the 5-G line is less than 3 m from the magnet center when the magnet operates at design field. This permits the magnet to be used within an experimental space commonly available within a university building.
A 4.7-T magnet with a 0.3 M bore for P-31 magnetic resonance spectroscopic imaging

   H. Maeda, M. Urata, T. Wada, T. Yazawa and A. Sato

Summary: A 0.3-m-bore, 4.7-T, high-homogeneity magnet, used for P-31 magnetic resonance imaging, has been constructed and installed. The magnets are comprised of a set of solenoids, which attained designed 94.8-A current (1.8 MJ) without quenching. Diodes in the cryostat resulted in a fast ramp rate of 3 T in 10 min. The field inhomogeneity for the bare magnet was -250 p.p.m./0.1 m dsv, which was finally reduced to 6 p.p.m./0.1 m dsv by shim coils. The field decay was less than 0.05 p.p.m./h. The magnet system is currently used for P-31 magnetic resonance spectroscopic imaging experiments on living animals in the laboratory.
600 MHz spectrometer magnet

   J.E.C. Williams, S. Pourrahimi, Y. Iwasa, L.J. Neuringer and L. Motowidlo

Summary: An NMR-grade superconducting magnet has been constructed which operates in persistent mode at 14.25 T at reduced temperature. The stored energy is 840 kJ. The magnet incorporates niobium-titanium and niobium-tin multifilamentary conductors. In the persistent mode all windings are in series with superconducting joints between sections. Six of the joints are hybrids, niobium-tin joined to niobium-titanium. The niobium-titanium windings reached short sample without training. The niobium-tin sections suffered two training quenches before reaching 14.25 T.
A full scale superconducting rectifier for powering an MRI-magnet

   J. Sikkenga and H.H.J. ten Kate

Summary: The design, construction, and experimental investigation of a full-scale superconducting rectifier is described. A short description of the principles of superconducting rectifiers is given. The results of the experiments are very satisfactory. The main goal, to establish the reliability of the superconducting rectifier as power supply for an MRI magnet system, was fully achieved. The demonstrated behavior of the rectifying system was as theoretically expected.
Transient characteristics of parallel running of the 20 kVA superconducting synchronous generator and a conventional one

   T. Nitta and T. Okada

Summary: A description is given of electrical transient characteristics of the parallel operation of a 20-kVA superconducting synchronous generator and a conventional one. In the experimental power system, the superconducting generator is connected through reactors (artificial transmission lines) to a regional power system (infinite bus), and the conventional generator (20 kVA) is connected to the terminal of the superconducting generator. Synchronous closing tests, loss of synchronism tests, and disconnecting and reclosing tests were performed. It was found that by installing a superconducting generator (SCG) in power systems, voltage stability and power system stability can be improved in transient states as well as in steady states, and the variation of armature current of SCG during a transient period is much larger than that of the conventional one. Simulation results in good agreement with the experimental results were also obtained.
Using a small hybrid pulse power transformer unit as component of a high-current opening switch for a railgun

   E.M.W. Leung, R.E. Bailey and P.H. Michels

Summary: The hybrid pulse power transformer (HPPT) is a unique concept utilizing the ultrafast superconducting-to-normal transition process of a superconductor. When used in the form of a hybrid transformer current-zero switch (HTCS), this creates an approach in which the large, high-power, high-current opening switch in a conventional railgun system can be eliminated. This represents an innovative application of superconductivity to pulsed power conditioning required for the Strategic Defense Initiative (SDI). The authors explain the working principles of a 100-kJ unit capable of switching up to 500 kA at a frequency of 0.5 Hz and with a system efficiency of greater than 90%. Circuit analysis using a computer code called SPICE PLUS was used to verify the HTCS concept. This concept can be scaled up to applications in the several mega-ampere levels.
Future development of large superconducting generators

   S.K. Singh and C.J. Mole

Summary: Scientific and technological progress in superconductivity and cryogenics that has brought the use of superconductors to reduce the electrical power dissipation in power equipment closer to reality are briefly reviewed. Recently completed US programs and current foreign and US programs are described. A US development program to maintain leadership in the field is proposed.
Impact of high temperature superconductors on pulsed power systems

   S.K. Singh, J.H. Murphy, P.W. Eckels, C.J. Mole, A.T. Male and C.K. Jones

Summary: Some recent parametric analyses conducted on a series of alternative baseline designs of 5-50-MVA pulsed AC generators with low-temperature-superconductor, high-temperature superconductor, and cryocooled windings are discussed with emphasis of the influence of operating temperature from liquid helium to liquid nitrogen coolant system design, conductor configuration, and consequent energy economics of the machine. These are related to the projected performance of a novel conductor concept presently under development.
Practical experience on the operation of a 320 kVA synchronous generator with a superconducting field winding

   H. Bischof, W. Engl, H.-P. Groter, H.W. Lorenzen and J. Schaller

Summary: Eight years of experiments carried out on a 320-kVA two-pole, external-pole-synchronous generator with a superconducting field winding. A summary is presented of practical experience and empirical results, which were obtained in 39 test cycles. On back-strokes, difficulties and problems concerning the generator and the whole test setup are reported as well as successes.
Controller action and control of a 330 kVA synchronous generator with a superconducting excitation winding

   H. Bischof, H.-P. Groter and H.W. Lorenzen

Summary: Theoretical and experimental investigations were conducted during the last two years on the control of a 330-kVA synchronous generator with a superconducting field winding. The generator is connected either to the mains or to an island network. The superconducting field winding of the two-pole external pole synchronous generator is cooled indirectly by supercritical helium in a closed cooling circuit. The machine is controlled digitally by microcomputers at grid or island operation. A summary is given of test results on controlled generator operation (load decrease, variation of active and reactive power). Measured values are compared to the values gained from simulation are discussed.
A comparison of the conductor requirements for energy storage devices made with ideal coil geometries

   W. Hassenzahl

Summary: Superconducting magnetic energy storage (SMES) plants have previously been proposed in both solenoidal and toroidal geometries. The former is efficient in terms of the quantity of superconductor required per unit of stored energy. For applications where a fringe field could be a problem, the toroidal geometry, which requires at least a factor of two more material, has been proposed. In addition to the solenoid and toroid, other geometries are possible, such as linear multipoles and spherical coils. These geometries have been considered for use in applications other than energy storage. Here the effectiveness (quantity of superconductor/stored energy) is calculated for various coil geometries.
Lightweight power bus for a baseload nuclear reactor in space

   C.E. Oberly, L.D. Massie and D.J. Hoffmann

Summary: Space environmental interactions with the power distribution/power processing subsystem can become a serious problem for power systems rated at tens to hundreds of kilowatts. Utilization of ceramic superconductors at 1000 A/cm/sup 2/, which has already been demonstrated at 77 K, in a conductor configuration may eliminate both bus mass and distribution voltage problems in a high-power satellite. The analytical results presented demonstrate that a superconducting coaxial power transmission bus offers significant benefits in reduced distribution voltage and mass.
Economic potential of applying HiT/sub c/ superconductors to magnetic energy storage

   J.-T. Eriksson and J. Korpijarvi

Summary: The authors verify the technical and economic specifications of SMES (superconducting magnetic energy storage) units of arbitrary sizes, i.e. to provide models for further, energy-management-related simulations. The weekly energy efficiency is based on a five/seven days discharge duty cycle (51 out of 52 weeks a year). The efficiency includes thermal heat leak through walls and reinforcement, current lead losses, power equipment losses, and nitrogen production losses. Superconductor AC losses and losses due to eddy currents in massive aluminum parts are the only major sources that the authors have not tried to estimate so far. The cost distribution of the 500-MWh facility is presented.
Experimental results of an experimental three-phase AC superconducting armature

   Y. Brunet, P. Tixador and P. Vedrine

Summary: Owing to the recent development of low-loss AC superconducting conductors, 50/60-Hz applications of superconductivity in electrical engineering can be developed, and power transformers and limiters, AC cables, and full-superconducting machines can be investigated. As a first step in the realization of a full-superconducting synchronous generator, a three-phase superconducting armature has been manufactured and tested with a normal rotor inside. Cryogenic and electrical tests have been made during more than 100 h, and include transients, connection to the power grid and asynchronous start-up and operation. The results are relevant for the next step of the experiment which is to complete a 20-kVA, 3000-r.p.m. machine with a superconducting rotating field winding, which is now under construction.
A two-phase full-wave superconducting rectifier

   T. Ariga and A. Ishiyama

Summary: A two-phase full-wave superconducting rectifier has been developed as a small cryogenic power supply of superconducting magnets for magnetically levitation trains. Those magnets will be operated in the persistent current mode. However, small ohmic loss caused at resistive joints, and AC loss induced by the vibration of the train cannot be avoided. Therefore, the low-power cryogenic power supply will be required to compensate for the reduction in magnet current. The superconducting rectifiers consists of two identical full-wave rectifiers connected in series. The main components of each rectifier are a toroidal superconducting setup transformer and two thermally controlled switches. The test results using a 47.5-mH-load magnet at 0.2 Hz and 0.5 Hz operations are described. To estimate the characteristics of the superconducting rectifier, the authors have developed a simulation code. From the experiments and the simulations, the transfer efficiency is determined.
Thermally and magnetically controlled superconducting rectifiers

   G.B.J. Mulder, H.H.J. ten Kate, H.J.G. Krooshoop and L.J.M. van de Klundert

Summary: The switches of a superconducting rectifier can be controlled either magnetically or thermally. The authors point out the differences between these methods of switching and discuss the consequences for the operation of the rectifier. The discussion is illustrated by the experimental results of a rectifier which was tested with magnetically as well as thermally controlled switches. It has an input current of 30 A, an output current of more than 1 kA and an operating frequency of a few Hz. A superconducting magnet connected to this rectifier can be energized at a rate exceeding 1 MJ/h and an efficiency of about 97%.
Method for critical current testing: software corrections

   M.B. Siddall and D.B. Smathers

Summary: A digital method for accumulating critical current date allows the test to be automated. Digital techniques provide the opportunity to make corrections for self field, protection shunt, and transient voltages which are not feasible with an analog system. Automation also allows rapid data analysis to inspect the test for bad data. The digital current incrementing method deviates from the ASTM test method, but the authors' measurements on the NbTi SRM and the Japan-US B sample from round robin testing show it to be accurate to within the limits set by ASTM.
The aluminum stabilized Nb-Ti conductor for the ZEUS thin solenoid

   R. Bruzzese, S. Ceresara, G. Donati, S. Rossi, N. Sacchetti and M. Spadoni

Summary: The ZEUS experiment, an experimental apparatus for high-energy physics that is to be installed on the hadron electron ring accelerator HERA at DESY-Hamburg, West Germany, will use a superconducting thin solenoid surrounding a number of particle detectors. The essential features of this magnet are 1.8-T magnetic field on the axis, 2.3-T maximum field on the conductor, inner diameter of 2 m, and solenoid length of 2.5 m. As physics requirements call for a total solenoid thickness less than 0.9 radiation length, a conductor consisting of a Rutherford-type Nb-Ti cable clad with a high purity aluminum has been developed. A report is presented on measurements of the main parameters needed for a complete characterization of a conductor to be used in this particular kind of magnet. Data on critical current, transfer length, and residual resistivity ratio are given and discussed, including the influence that the various fabrication steps can have on them.
Training in test samples of superconducting cables for accelerator magnets

   A.K. Ghosh, M. Garber, K.E. Robins and W.B. Sampson

Summary: In the critical current measurement of some high-current NbTi cables, the samples have to be 'trained' by repeated quenching to obtain a usable voltage-current curve for I/sub c/ determination. This training behavior is most pronounced when the applied field is perpendicular to the wide face of the conductor and is strongly dependent on the copper-to-superconductor ratio and the clamping pressure. Data are given for SSC (Superconducting Super Collider) prototype cables as well as for HERA production conductors. Although a quantitative understanding of the experimental data is still lacking, some speculations regarding stability are presented.
The effect of transverse stress on the critical current of Nb/sub 3/Sn cable-in-conduit superconductors

   L.T. Summers and J.R. Miller

Summary: An investigation has been conducted of the effects of transverse stress on the critical current of Nb/sub 3/Sn cable-in-conduit conductors (CICC). The sensitivity of the critical current (I/sub c/) to applied stress at 12 T has been determined for CICCs with helium void fractions (f/sub He/) in the range of 0.25-0.4. I/sub c/ has been found to be a function of transverse stress with good correlation with single-wire data up to stress levels of 50 MPa. At higher stress levels with the CICCs show significantly higher degradation with transverse stress. No clear correlation has been found between the stress sensitivity of I/sub c/ and f/sub He/. The results fall into a broadband, suggesting that geometric factors, such as wire position within the cable bundle, exert a strong influence on the I/sub c/ vs. stress dependence.
Flux creep in a Tevatron cable

   M. Kuchnir and A.V. Tollestrup

Summary: The authors measured the slow magnetization decay of short sample (2.3 cm) of Tevatron cable in fields up to 0.3 T. The special susceptometer in development for these measurements is based on a commercial SQUID (superconducting quantum interference device) and is described in detail. The observed decay is logarithmic in time as expected from flux creep in the NbTi filaments. A strong correlation was found between the decay and the magnetization status of the sample. It is too early yet to present a quantitative correlation between what the authors observed and the decay observed in the sextupole component of Tevatron dipoles. The detailed understanding of this phenomenon may be instrumental in guiding the search for efficient superconducting synchrotron operational procedures.
Self field effects on the superconducting to normal transition of S/C cables

   P. Fabbricatore, P. Fernandes, R. Parodi and R. Vaccarone

Summary: The onset of the transition of a superconducting (S/C) cable to the normal state is described by the relation V=V/sub c/ (the critical voltage, i/sup n+1/) where V is the voltage drop per unit length, V/sub c/ the critical voltage, i the reduced current I/I/sub c/ (I/sub c/ is the critical current), and n an integer ranging from 10 to 40 depending on the cable quality. A correct evaluation of the critical current and n value must take into account the effects due to the self-field at the cable. For high-current cables the self-field can affect the measurement by about 15%. A theoretical model is developed and it is applied to the results obtained in the critical current measurements of the S/C cables for HERA dipoles. It is found that the critical current and n are strongly dependent on the self-field.
Application of current simulation method for calculating magnetic field of superconducting AC generator

   Qingfu Li and Fei Wang

Summary: A current simulation method is presented for calculating the three-dimensional magnetic field of a superconducting AC generator. The method represents the influence of the boundaries by a large number of current loops appropriately positioned at a distance behind the boundary surface so that the boundary conditions on the actual surface of the boundaries are satisfied. The calculated results obtained for the model of the superconducting AC generator are close to the measured values.
Application of image method to calculate 3-D magnetic field and parameters of SC alternator

   Qingfu Li and Fei Wang

Summary: The image method has been used for calculating the three-dimensional magnetic field and parameters of a superconducting AC generator. The method can represent the actual shape of the coils and take account of the conductor cross-section. The influence of the magnetic and conducting boundaries are represented approximately by their images in the boundaries. The influence of either conical or stepped boundaries in the end region is represented by forming images on an adjustable conical surface in association with the boundary condition, improving the accuracy of the calculation.
Considerations against a force compensated coil

   W. Hassenzahl

Summary: The cost of structural components in a large superconducting coil such as SMES may well exceed the coil and cryostat cost. As a result, the idea of constructing a system composed of two different coil types assembled in such a way that the forces balance and reduce the total structural requirement is often proposed. A suitable geometry has never been found for the fundamental reason that there can be no force-compensated solution. The general problem is presented, and an analysis of the energy stored and stresses produced in the structure is described in a fundamental way. Finally, relation between structural mass M and stored energy E that is valid for all magnetic systems is developed.
Structure optimization of space borne toroidal magnets

   X. Huang, Y.M. Eyssa, M.K. Abdelsalam, L. El-Marazki, M.H. Abdelmohsen, M.A. Hilal and G.E. McIntosh

Summary: An optimization study aimed at minimum weight under certain constraints on module size and weight has been carried out. This study includes a structural material survey of materials with high specific strength and modulus, and an analysis of the effectiveness of coil configuration parameters on the value of E/M, energy stored per unit mass. Some typical structure problems, such as buckling in the bucking cylinder, are also discussed.
Nb/sub 3/Sn coating of high purity Nb cavities

   D. Dasbach, G. Muller, M. Peiniger, H. Piel and R.W. Roth

Summary: The authors have developed a modified vapor diffusion technique using specially constructed UHV furnaces to produce uniform Nb/sub 3/Sn layers on 1- and 3-GHz accelerator cavities without losing the high thermal conductivity of the Nb wall. In a first experiment with a single-cell 3-GHz cavity of medium Nb purity (residual resistivity ratio, RRR=156) they have achieved E/sub acc/=10 MV/m with an 0.6- mu m-thick Nb/sub 3/Sn layer. This is so far the highest accelerating field for their Nb/sub 3/Sn cavities, but it is low compared to the 25 MV/m achieved in the same cavity before coating. Possible reasons for the reduced breakdown field for Nb/sub 3/Sn are discussed on the basis of the local thermal breakdown model.
Superconducting properties of B1 nitrides film obtained by gas-metal reaction for RF application

   P. Fabbricatore, P. Fernandes, G.C. Gualco, R. Musenich and R. Parodi

Summary: The authors investigated the RF behavior of the B1-type superconductors NbN obtained by reacting reactor-grade niobium samples in high-purity (10 p.p.m. of total impurities) nitrogen atmosphere after a baking at high temperature (800 degrees C) in an UHV furnace. They obtained a critical temperature of 14.6 K for a tetragonally distorted cubic lattice with cell parameters a=4.381 AA and c=4.324 AA, as determined by X-ray diffraction. The RF test showed for the resonator, operating at 4.5 GHz, a surface resistance at 4.2 K of 1 mu Omega in good agreement with the value predicted by the BCS theory.
Influence of condensed gases on field emission and the performance of superconducting RF cavities

   Q.S. Shu, K. Gendreau, W. Hartung, J. Kirchgessner, D. Moffat, R. Noer, H. Padamsee, D.L. Rubin and J. Sears

Summary: In a program to study the field emission (FE) and to improve the performance of one-cell 1500-MHz superconducting Nb microwave particle accelerator cavities, the authors recently achieved peak surface fields as high as 51 MV/m through the use of 1200 degrees C UHV annealing, methanol rinsing, and high-power He processing. Performance is limited by excess FE from localized points on the cavity walls. Cycling of these cavities to room temperature and admission of He processing gas frequently produce large changes in Q correlating with the appearance or disappearance of the dominant field emitter, suggesting that condensed residual and impurity gases play a significant role in enhancing FE. By intentionally condensing O/sub 2/ into a cold cavity, the authors have produced similar effects, increasing the dissipated power and reducing Q, each by an order of magnitude at the same field level. Preliminary tests have also been carried out with H/sub 2/ and water vapor. These results suggest that improvements in the outgassing and vacuum environment of these cavities may be important.
A laboratory superconducting high gradient magnetic separator

   L.G. Yan, Y.J. Yu, Z.K. Wang, Z.Y. Kao, Z.X. Ye, C.L. Xue, P. Ye, Y.L. Cheng, X.M. Li, Q.W. Kong, S.S. Song, H.L. Nan, Y.M. Dai and H.T. Tang

Summary: To determine the effectiveness of high-gradient magnetic separation (HGMS) for kaolin clay purification and coal desulfurization in China and to develop suitable technology, a superconducting HGMS facility has been constructed and put into operation. The working separation chamber is 80 mm in diameter and 400 mm in length. The magnet is wound with 0.75-mm and 0.5-mm diameter NbTi superconducting composite. The winding is compact and wax-filled. Tests prove that the magnet can operate at 5 T. Special attention has been paid to design and construction of the magnet cryostat. In the wet benefication mode, there are two separation systems available; one is an upward pumping feeding system and another is downward gravity feeding. The rate of flow and the linear velocity are 0-0.5 L/s and 0-100 cm/s, respectively. Preliminary sample test results for kaolin clay purification and coal desulfurization show the feasibility of magnetic separation.
Superconducting permanent magnets

   S.L. Wipf and H.L. Laquer

Summary: The authors discuss means to verify the analysis and the limitations imposed by the low critical current densities in presently available high-temperature superconductors. Based on experimental data, it is concluded that : (1) high-temperature superconductors can be used as permanent magnets with trapped fields of at least 3 T at 77 K; (2) their energy product should be as high as 1.8 MJ/m/sup 3/ or 255 MG-Oe; (3) the magnetizing field has to be four times as large as the trapped field, or 12 T; (4) permanent-magnet use of high-temperature superconductors bypasses the problems of wire or tape manufacture; and (5) widespread use of this concept will depend on improved critical current densities.
The investigation of the superconducting NMR-imaging main magnets

   Y. Zhang, S. Han and Z.X. Feng

Summary: The design principles of MRI (magnetic resonance imaging) main magnets and the problems in the design process are analyzed. A computer program in which the critical characteristics of superconductor, the uniformity of the magnetic field, the economization of the magnet, and the selection of magnet constructions are considered has been established. The program can also be used to design high-uniformity superconducting magnets in some other uses. Five different magnet constructions are treated. By analyzing the computer results some conclusions useful for the practical design of the magnets are obtained.
Optimal design of MRI magnets with magnetic shielding

   A. Ishiyama, M. Hondoh, N. Ishida and T. Onuki

Summary: A novel optimal design method has been developed for a highly homogeneous superconducting coil system with magnetic shielding for magnetic resonance imaging (MRI). The design method is based on a combination of the hybrid finite-element-boundary-element method for analysis of an axially symmetric nonlinear open-boundary magnetic-field problem and a mathematical programming method for solving the corresponding optimization problem. The goal programming and the nonlinear least-squares methods have been adopted. The relative merits of a combination of an active shielding and a room shielding have been investigated. The proposed design method can optimize both an MRI magnet and its magnetic shielding system simultaneously, taking into account the maximum permissible intensity of stray field at a specified distance from the magnet center. Several design procedures and results of a 1-T magnet system are shown.
Magnetic shielding by a tubular superconducting winding in parallel and transverse fields

   K. Takahata, S. Nishijima, M. Ohgami, T. Okada, S. Nakagawa and M. Yoshiwa

Summary: The shielding efficiency for parallel and transverse fields was examined using three types of shield, and the possibility of magnetic shielding with superconducting multifilament wire was investigated. It was concluded that the magnetic shields with superconducting windings could shield not only the parallel but also the transverse fields to the axis. The stability of the superconducting shield is discussed.
Development of superconducting networks for a large scale magnetic shield

   K. Takahata, S. Nishijima, T. Okada, S. Nakagawa and M. Yoshiwa

Summary: The shielding capabilities of a multiringed disk were analyzed to design the shielding networks. The applicability to a large-scale shield was examined experimentally and four conclusions are drawn: (1) the multiringed shields show the highest performance when the diameter of the rings is half of that of the disks; (2) if the diameters of the rings are adequate, a multiringed shield can control the field distribution; (3) the shielding efficiency is almost independent of the external field and the field sweep rate when the shielding currents in the rings does not exceed the effective critical current; when the shielding current reaches the effective critical current, the efficiency decreases with increasing external field, and in this case, flux jumps are apt to occur; and (4) for a large-scale shielding network, the effective critical current of rings must be enlarged.
CEBAF superconducting spectrometer design

   P. Brindza, J. Alcorn, R. Carlini, L. Harwood, J. LeRose, B. Mecking, J. Mougey and J. O'Meara

Summary: The CEBAF (Continuous Electron Beam Accelerator Facility) Experimental Nuclear Physics Program is based on three independent facilities, each with unique capabilities. Hall A consists of a pair of high-resolution spectrometers (HRSs), hall B features a large acceptance spectrometer (LAS), and hall C will have a high-acceptance, high-energy electron spectrometer and matching special-purpose hadron spectrometer. The authors demonstrate that the performance and operational requirements of these devices can be met effectively through the use of superconducting devices. The physics requirements and the rational basis for design selection are discussed. An analysis that supports the cost-effectiveness of the selected design is presented. The cryogenic system is covered as well as the integration of the experimental hall cryogenic system and main CEBAF central helium refrigerator.
A superconducting toroidal magnet for the CEBAF large acceptance spectrometer

   J. O'Meara, J. Alcorn, P. Brindza, M.-S. Chew, G. Doolittle, M. Fowler, B. Mecking, C. Riggs, D. Tilles and W. Tuzel

Summary: The CEBAF (Continuous Electron Beam Accelerator Facility) physics program requires a large acceptance spectrometer covering nearly all of the 4 pi solid angle for studying complex electronuclear interactions. This device relies on a six-coil toroidal magnetic field to provide momentum analysis. The desire to maximize solid angle coverage led to a thin superconducting toroid design. The main device has an outside diameter of 4.6 m, an active length of 5 m, a peak field in the toroidal volume of 1.2 T, and a stored energy of 18 MJ. An intrinsically stable design was selected to minimize the overall space requirements of the toroid. The individual coils of the toroid are approximately kidney-shaped; the negative curvature provides a field-free region for targets coming from the requirement to have good particle focusing properties. The overall design is presented.
A superconducting dipole concept for the CEBAF high resolution spectrometers

   J. Alcorn, P. Brindza, M. Fowler, L. Harwood, T. Hunter and W. Tuzel

Summary: CEBAF (Continuous Electron Beam Accelerator Facility) requires a pair of high-resolution spectrometers (HRS) for performance of electron/hadron coincidence experiments at up to 4 GeV/c. Momentum analysis for each arm is provided by a 45 degrees vertical bending dipole having a useful field volume 6.0 m long * 30-40 cm wide (pole gap) * 80 cm high. A resistive 30-cm-gap dipole has been selected for the reference 4-GeV/c HRS, utilizing a qQQDQQ magnet configuration. However, recent studies aimed at equipment cost reduction indicate that a 40-cm-gap superconducting dipole based on less stringent field uniformity requirements may be attractive, either with the reference HRS or with a revised design, using fewer magnet elements. The concept described is an H-frame superconducting magnet, with contoured poles and resistive interpole field shaping coils, to achieve a field quality of 1 G/cm across the aperture at all useful excitation levels. This approach yields minimal pole width and requires only conventional fabrication tolerances.
A superconducting iron-dominated quadrupole for CEBAF

   L.H. Harwood, S. Lassiter and W. Tuzel

Summary: The current design for the high-resolution spectrometers at CEBAF (Continuous Electron Beam Accelerator Facility) requires a front quadrupole that has a gradient * length of 6.8 T with a 'good field' aperture (1*10/sup -3/ uniformity in gradient) of 16 cm radius. A room-temperature design was found too power hungry and interferred with the beam. Engineering and construction of a small cos 2 theta magnet was considered to be quite expensive. A Panofsky design was not considered due to the extreme sensitivity of the field quality to errors in conductor placement. A conformal mapping of a window-frame dipole into quadrupole geometry worked well. A conceptual design has been developed with the following characteristics: physical length (total)=1.2 ; iron length=1.1 m; iron outer dimensions=54 cm*80 cm; peak gradient=6.2 T/m; pole radius=20 cm; 'good field' radius=16 cm; coil peak field=1.5 T; conductors=1 mm diameter; Cu/NbTi=7:1; current=400 A; turns=250/quadrant; and stored energy=50 kJ.
A superconducting cos 2/spl theta/ quadrupole design for the CEBAF high resolution spectrometer

   W. Tuzel, J. Alcorn, P. Brindza, A. Gavalya, J. Mougey and S. Nanda

Summary: The pair of high-resolution spectrometers at CEBAF (Continuous Electron Beam Accelerator Facility) require large-aperture, high-gradient quadrupoles. A superconducting cos 2 theta design is under consideration to meet these requirements. The quadrupole has a coil diameter of 1 m and a peak gradient of 5 T/m with an effective field length of 1.8 m. The stored energy of this quad is 3.0 MJ. The details of the design of the coil, shrink fit support collar, and cryostat are presented. The analysis of the superconductor, quench behavior, and coil protection system is covered.
Microstructure control in high Ti NbTi alloys

   P.J. Lee, J.C. McKinnell and D.C. Larbalestier

Summary: The microstructures of five high-Ti NbTi alloys (Nb49-62-wt.%Ti) and a ternary Nb-54-wt.%Ti, 4-wt.%Zr alloy have been observed following heat treatments of 80 h at 420 degrees C at prestrains of between 8.3 and 12.6. It was found that increasing prestrain suppressed the formation of deleterious Widmanstatten alpha -Ti and omega phases and that the higher the Ti content, the higher the prestrain required for elimination of these forms of precipitation. The Zr addition increased the precipitation rate and reduced the precipitate size without promoting the formation of Widmanstatten alpha -Ti or omega .
Fine filament NbTi conductors for the SSC

   H.C. Kanithi, C.G. King, B.A. Zeitlin and R.M. Scanlan

Summary: Inner and outer grades of wire have been processed with NbTi filament diameters of 5 to 9 mu m, depending on the magnet design requirements. An increase in billet diameter from 10-in to 12-in resulted in an improved critical current density approaching 3000 A/mm/sup 2/ at 5 T. The authors report on the electrical properties (J/sub c/ and n value) and mechanical properties (tensile, springback, and bend characteristics) of the strand. Piece length distributions obtained for various production billets are presented. The performance of cables fabricated from the strand is discussed. Specifically, the critical current degradation due to cabling and residual twist in the cable are addressed.
A conductor, with uncoupled 2.5 mu m diameter filaments, designed for the outer cable of SSC dipole magnets

   E. Gregory, T.S. Kreilick, J. Wong, E.W. Collings, K.R. Marken Jr., R.M. Scanlan and C.E. Taylor

Summary: A conductor with a stabilizer-to-superconductor ratio of 1.8/1 and containing 22900 2.5- mu m diameter filaments at a wire diameter of 0.65 mm has been produced for the outer cable of the Superconducting Super Collider (SSC). The fabrication procedures used to make this material from a full production-size billet 305 mm in diameter are described. Metallographic, electrical, and magnetization data are presented, and these illustrate the filaments are completely uncoupled at the size used in the outer SSC cable. This work indicates the feasibility of the commercial manufacture of such a 2.5- mu m-diameter filamentary material. Preliminary tests show relatively low J/sub c/ and n values. It is likely that materials with smaller spacings than those used here will be required before the J/sub c/ values specified for the SSC can be obtained reproducibly.
The effect of titanium content on the pinning force in Nb44wt.%Ti to Nb62wt.%Ti

   J.C. McKinnell, P.J. Lee and D.C. Larbalestier

Summary: The authors have been studying high Ti alloys to establish whether they offer higher low-field J/sub c/ values than Nb46.5wt.%Ti and find that they do, with values, as high as 7500 A/mm/sup 2/ at 2 T, 4.2K. They have established that the pinning centers are alpha -Ti precipitates for all alloys from Nb44wt.%Ti to Nb62wt.%Ti, but find a steady shift in the pinning curve peak to lower reduced fields at 4.2 K. Recently, it was shown that both Delta H/sub c/ and Delta kappa pinning can be recognized in Nb47wt.%Ti. Since T/sub c/ and H/sub c/ vary rapidly in the high Ti alloys, Delta H/sub c/ pinning should be proportionately stronger in the high Ti alloys, leading to a displacement of the peak in the pinning force curves to lower fields. The authors present pinning force data at 1.8 K and 4.2 K across the alloy range and find that while lower Ti alloys do exhibit b(1-b) behavior, the higher Ti alloys never realize b/sup 1/2/(1-b)/sup 2/ behavior.
High current density of NbTi composite

   S. Hong, D. Geschwindner, A. Mantone, W. Marancik, S. Zalek and R. Zhou

Summary: Various NbTi composites that can sustain very high current density are reported. J/sub c/=3000 A/mm/sup 2/ in a 5-T background field has been achieved with 0.85-mm-diameter wire for production and J/sub c/=38000 A/mm/sup 2/ has been achieved in some experimental composites. The development results on a fine filament composite to be used in conjunction with SSC are reported.
Refinements in billet design for SSC strand

   P. Valaris, T.S. Kreilick, E. Gregory and J. Wong

Summary: Refinements in the design of superconducting strand to be used in the manufacture of magnets for the Superconducting Super Collider (SSC) are described that have considerably improved performance characteristics in key areas; first, by maintaining geometric uniformity and second, by contributing to piece length yield. With 2.5- mu m-diameter filaments and a copper-to-superconductor ratio of 1.8:1, the total number of filaments required is approximately 23000. Stacking hexagon units and reducing the amount of void space has enabled the production of largely uniform arrays and consequently uniform spacing. A strand with approximately 23000 fine filaments has been produced with a mostly uniform filament array.
The effect of self field on the critical current determination of multifilamentary superconductors

   M. Garber, A.K. Ghosh and W.B. Sampson

Summary: In determining the short sample critical current of conductors of large cross section or high current density, the self-field produced by the transport current must be taken into account to obtain a true value for the critical current. A simple model calculation for determining this effect is described. Measurements on wires, cables, and monoliths show the validity and self-consistency of the procedures.
Reduction of AC losses in ultra-fine multifilamentary NbTi wires

   J.R. Cave, A. Fevrier, T. Verhaege, A. Lacaze and Y. Laumond

Summary: The authors present AC loss measurements for a series of wires in which the proximity effect has been greatly reduced by increasing the distance between the filaments while retaining high values of the overall critical current density, typically 3000 A/mm/sup 2/ at 0.5 T. For the best performing wires, 50-Hz AC losses in W/(Am) (=(losses in W/m/sup 3/)/(overall J/sub c/ in A/m/sup 2/)) for small test coils are a factor of ten lower for 0.5-T peak field and a factor of three lower at 1-T peak field. For wires with negligible proximity coupling, losses at low fields are reduced compared to that calculated by the Bean model, due to the small number of flux lines that thread across the width of each filament.
Current capacity degradation in superconducting cable strands

   L.F. Goodrich and S.L. Bray

Summary: The electromagnetic properties of NbTi strands extracted from Rutherford cables were studied to clarify the effect of mechanical deformation, caused by the cabling process, on the current capacity of the strands. Three different cables were studied, all of which are prototypes for the Superconducting Super Collider's dipole magnets. The extracted cable strands were instrumented to allow measurement of the voltage across several key regions of mechanical deformation as a function of current and the orientation of the applied magnetic field. The resulting data are presented in terms of the strand's voltage profile as well as its critical current to more thoroughly characterize the conductor's electromagnetic properties. The cable strands show very localized reductions in current capacity that are well correlated with the regions of high mechanical deformation.
Magnetic evaluation of Cu-Mn matrix material for fine-filament Nb-Ti superconductors

   R.B. Goldfarb, D.L. Ried, T.S. Kreilick and E. Gregory

Summary: The authors have examined some of the magnetic properties of Cu-Mn alloys with Mn content in the range 0.16 to 3.75 wt.% to determine whether spin-glass effects could impair the performance of fine-filament Nb-Ti conductors. It appears that for Mn content in this range, the adverse magnetic properties of the matrix are not significant. Magnetization and susceptibility measurements show that adverse magnetic effects arising from spin-glass properties are minimal for concentrations of Mn up to at least 4%.
The critical current of NbTi multifilamentary wire: a comparison between critical current densities using AC magnetization techniques (J/sub CM/) and DC transport measurement (J/sub CT/)

   D.P. Hampshire and D.C. Larbalestier

Summary: AC magnetization measurements are presented for transverse field orientation on a NbTi standard reference material supplied by the National Bureau of Standards. These data, generated in DC background fields for the range 0
Calculations of plastic strain and resistivity increase in a composite conductor subjected to cyclic strain

   K.T. Hartwig, J.T. Gehan and G.L. Richards

Summary: Graphical calculations are presented for plastic strain per cycle and accumulated plastic strain in aluminum composite conductors subjected to cyclic strain at 4.2 K. The graphical model is based on a constant-strain-range experiment with monolithic pure aluminum. Calculations are derived from synthesized stress-strain hysteresis loops. The resistivity increase expected from force controlled cyclic stress is shown to be substantially less than that arising from constant strain range cycling. Suggestions are given for decreasing resistivity degradation in the composite conductors of cycled magnets.
Intermediate scale industrially processed Nb/sub 3/Sn(Ti) by powder metallurgy

   S. Pourrahimi, C.L.H. Thieme and S. Foner

Summary: Powder metallurgy processing of Nb/sub 3/Sn(Ti) wire was scaled up to 75-mm-diameter billets, each containing 4 kg of pressed powder composite. Prealloyed Nb-1.5-wt.% Ti powder was used for optimum high-field properties. An initial hot extrusion step provided complete consolidation and excellent integrity of the powder composite. Using the extruded bars, various single and multiple tin core billets were prepared and hydrostatically extruded to 12-mm-diameter bars. Long lengths of internal tin core wire were drawn without any breakage to less than 1 mm diameter. To evaluate the performance of long-length wires, small magnets were fabricated from these wires and tested in background fields of water-cooled Bitter magnets up to 20 T. The processing, performance, and microstructure of these small magnets are discussed. This intermediate-scale process used conventional metal-forming techniques that can be scaled to larger scale industrial processing.
Hysteresis losses in hollow superconductors

   J.A. Eikelboom, R.A. Hartmann and L.J.M. van de Klundert

Summary: Flux penetration into a hollow superconducting filament in a time-varying transverse magnetic field is determined numerically. The magnetization of the filaments is calculated for field variations below and above the penetration field of the filament. The influence of the inner radius of the superconducting filament on the magnetization and the hysteresis losses in the filament is shown. The critical current density is taken to be constant during the external field cycle and depends within the superconducting filament on the local magnetic field, which is the sum of the externally applied field and the field induced by the local screening currents. Calculations based on the theory presented here show good agreement with experimental results.
Mo-Re superconducting thin films by single target magnetron sputtering

   A. Andreone, A. Barone, A. Di Chiara, G. Mascolo, V. Palmieri, G. Peluso and U. Scotti di Uccio

Summary: The authors prepared Mo/sub 60/Re/sub 40/ thin films by single target magnetron sputtering. All the films analyzed exhibited a sharp superconductive transition and values of the critical temperature T/sub c/ up to 13 K were achieved. Structural analyses (EDS and X-rays) were performed on the samples. A15 phase was obtained even at low deposition temperatures. From the measured low temperature resistivity O/sub c/ and critical temperature T/sub c/ an estimate of the theoretical BCS surface resistance is inferred and compared with that of niobium.
The influence of transverse, compressive stress on the critical current of multifilamentary Nb/sub 3/Sn and NbTi wires

   H. Boschman, P.P.E. Fornerod and L.J.M. van de Klundert

Summary: To investigate the critical current of multifilamentary wires as a function of the applied field and transverse compressive stress, a special experimental arrangement has been developed. The repulsive Lorentz force generated by a set of magnets is used to press a sample between two parallel surfaces. From the first experimental results on a multifilamentary NbTi wire, it is concluded that this approach functions properly.
Mechanical properties of composite conductors containing niobium filaments in bronze matrix

   A.D. Nikulin, A.K. Shikov, A.E. Vorob'eva, I.V. Golikov, I.I. Davydov, V.N. Shishov and T.N. Izmailova

Summary: A discussion is presented of an investigation into mechanical properties of multifilamentary composites 0.3-1.5 mm in diameter and containing up to some tens of thousands of Nb filaments in a bronze matrix. The influence of design features, geometrical sizes, and heat treatment schedules on the strength and plasticity of the materials was studied. Using metallographic and electron microscopic analysis, data were obtained on the structure and morphology of multifilamentary conductors that give an explanation of the observed differences in the mechanical properties of the composites discussed.
Nb/sub 3/Al formation process in powder metallurgy processed wires and sputtered multilayer films

   K. Watanabe, K. Noto, H. Morita, H. Fujimori and Y. Muto

Summary: The formation of Nb/sub 3/Al by a solid-state reaction between Nb and Al is examined for both powder-metallurgy-processed wires and sputtered multilayer films. It is found that the diffusion of Al into the Nb layer plays an important role in the formation of Nb/sub 3/Al. However, an extremely thin Nb film is not necessarily needed for the solid-state reaction, as indicated by the results obtained with multilayered films. A discussion is presented of the relationship of the Nb layer thickness and the areal reduction ratio to Nb/sub 3/Al formation in the powder-metallurgy process.
Comparison of Al5-Nb/sub 3/Al superconductors produced by laser alloying and infiltration

   W. Schaper, M. Kehlenbeck, I. Zimmermann and H.C. Freyhardt

Summary: Nb/sub 3/(Al, Si, Bi) and Nb/sub 3/Al superconductors were successfully prepared by a laser alloying and an infiltration process. Continuous CO/sub 2/ laser irradiation of Nb-sheathed Nb-25-at.% Al composite tapes prepared by a conventional powder metallurgical method was carried out. For a laser power of less than 3.5 kW and specimen velocities up to 30 m/min, almost stoichiometric Nb/sub 3/Al with critical temperatures of 16.6 K and critical current densities of 10/sup 4/ A/cm/sup 2/ at 15 T was obtained. For infiltration, sintered Nb powder was immersed in a liquid (Al/sub 88.7/Si/sub 11.3/)/sub 99/Bi/sub 1/ alloy. Subsequently the infiltrated rod was deformed and reacted at temperatures up to 2000 degrees C. The microstructure and the superconducting properties have been studied as a function of the degree of deformation and the reaction temperature. Critical temperatures between 14 and 18 K, upper critical fields B/sub c2/ of 21 T and critical current densities of 10/sup 4/ A/cm/sup 2/ at 16 T were obtained.
Nb/sub 3/Al wire produced by powder metallurgy and rapid quenching from high temperatures

   C.L.H. Thieme, S. Pourrahimi and S. Foner

Summary: Powder-metallurgy-processed Nb-25-at.% Al wires were annealed at temperatures just below the melting temperature. Depending on anneal conditions, the entire Nb-Al part of the wire could be rapidly quenched as a metastable Al Nb(Al) solid solution with an Al concentration exceeding 23 at.%. This A2 phase is sufficiently ductile to be bent without incurring damage. A second anneal at 950 degrees C converted the A2 into A15. J/sub c/ was 10/sup 4/ A/cm/sup 2/ at 22 T, and T/sub c/ was 17.8 K. The rapid quenching of Nb-Al powder metallurgy processed wire is a possible alternative to obtain improved high-field properties.
Further studies of a laser quenched superconducting opening switch

   T.L. Francavilla, H.H. Nelson, A.P. Baronavski, S.A. Wolf, D.U. Gubser and R.A. Hein

Summary: NbN films were prepared on planar sapphire and on small-diameter cylindrical quartz and sapphire substrates. Films prepared on cylindrical substrates had a greater critical current density than those prepared on planar substrates. The highest current densities of 1*10/sup 7/ A/cm/sup 2/ were achieved on cylindrical sapphire substrates. Measurements of the laser power required to drive the switch into the normal state were made as a function of current being carried by the NbN-clad sapphire rod. These experiments indicated that near J/sub c/ very small amounts of laser energy were needed to drive the sample normal as expected. At current values well below J/sub c/, much larger energies were required. These large energies, which are roughly 10/sup 3/ larger than the condensation energy, were attributed to heating of the sapphire rod necessary to raise the NbN above its transition temperature. The desirable properties of a superconducting switch are the ability to carry large currents in the superconducting state and have a high resistance in the normal state. Considerations for using the high-T/sub c/ oxides in a superconducting switch are examined.
Superconducting properties of TaN and VN films

   V.M. Pan, V.G. Prokhorov, V.A. Komashko, G.G. Kaminsky, M.A. Kousenetsov and C.G. Tretiatchenko

Summary: Thin superconducting TaN and VN films produced by reactive cathode sputtering have been investigated. Superconducting-phase-transition smearing in applied field seems to be due to spatial fluctuations of the electron diffusion coefficient as well as dimensional crossover of dynamical superconducting order parameter fluctuations. Flux pinning occurs at grain boundaries by electron scattering mechanism. Transition to a dissipative state is induced by flux line separation from the pins but not by flux line lattice plastic shear.
Effects of alloying on the superconducting properties of ErBa/sub 2/Cu/sub 3/O/sub 7/

   C.S. Pande, H.A. Hoff, A.K. Singh, M.S. Osofsky, M.A. Imam, K. Sadananda and L.E. Richards

Summary: In high-T/sub c/ superconductors, the low critical current densities in polycrystalline materials have been attributed to a combination of critical current anisotropy and poor superconducting coupling across grain boundaries. Theoretical calculations indicate that although the flux pinning should vary roughly inversely as grain size, the polycrystalline critical current behavior could possibly be understood in terms of stresses due to the grain boundary. Experiments have been conducted to increase the coupling between adjacent grains by modifying grain boundary chemistry. These include adding either a conducting layer or a superconducting layer at the interfaces. The effect of additions such as Ag, B, Bi, Ga, and In to produce a conducting layer and the alloying of RBa/sub 2/Cu/sub 3/O/sub 7/ with another superconductor to produce a superconducting layer were analyzed by measuring T/sub c/ and J/sub c/ and observing changes to the microstructure. Early results indicate some J/sub c/ enhancement with silver addition. However, the addition of a different superconductor appears more promising.
Preparation of dense bulk high T/sub c/ superconducting materials using hot isostatic pressing

   M.A. Imam, A.K. Singh, K. Sadananda and M. Osofsky

Summary: Sintered superconducting materials were encapsulated in evacuated stainless-steel or pyrex glass containers and processed in a hot isostatic pressing (HIP) unit at high temperatures and pressures. Optimum HIP conditions to obtain bulk samples of nearly theoretical density were determined. Results indicate that in addition to density, HIP also improved T/sub c/. For the one-two-three system, the grain size is significantly reduced during HIP. This is attributed to fracturing of coarse particles in the sintered compact due to high strain rates experienced during the pressurization. HIP materials can be machined to any shape and size, and the process being used for making specimens for J/sub c/ measurements and superconducting devices.
Properties of high-T/sub c/ oxide fibers from laser heated pedestal growth

   J.Z. Sun, R.S. Feigelson, D. Gazit, D. Fork, T.H. Geballe and A. Kapitulnik

Summary: Bi-containing oxide superconductors have been made into fine fibers using the laser-heated pedestal growth (LHPG) method. These fibers grow with the c-axis of the grain normal to the growth direction. Studies of critical currents obtained by pulsed-current transport measurement and by magnetic shielding studies are compared. The transport and magnetic properties are promising for 60-Hz power applications and devices where the current is maintained by an outside source and a small amount of dissipation can be tolerated. Low pinning barriers and consequently appreciable flux creep seem to be intrinsic characteristics of the high-T/sub c/ oxide superconductors. To utilize them in situations where persistent currents are required, it will be necessary to incorporate more pinning centers.
Bi-Sr-Ca-Cu-O bulk superconductors with zero resistance above 110 K

   H.S. Huang, S.N. Mao, Z.T. Yao, M.L. Liu, X.D. Ren, K.S. Zhang, Z.Y. Wu, X. Zhao and Y.-Z. Liu

Summary: Optimized processing to obtain bulk superconductors in Bi-Sr-Ca-Cu-O system with zero resistance above 110 K has been studied. The superconducting path of the high-T/sub c/ phase has been realized in multiphase polycrystalline samples. The resistance of a typical sample reaches zero at 111 K. The usual resistive tail extended to 80 K has been successfully cut off. The importance of the role CuO played in the sintering reactions for the formation of the 110 K phase is discussed on the basis of the results of DTA (differential thermal analysis) and TG experiments.
Preparation and characterization of magnetically textured Y and DY 123 compounds

   J. Seuntjens, X. Cai and D.C. Larbalestier

Summary: The authors prepared homogeneously (i.e through volume-textured material in comparison to sinter-forged samples where the texture is preferentially at the surface) c-axis-textured samples with approximately 200 mu Omega -cm resistivity at 100 K and approximately 88% density by aligning powders in a magnetic field and then sintering. Light microscopy, X-ray diffraction, and transport J/sub c/ measurements were used to characterize the samples. Longer sintering times improved the texture. Dilute suspensions in which particles did not touch could be very well aligned. Such samples, encased in epoxy, had 50% of
Zero resistance above 100 K in Bi-based superconductors

   S.M. Green, C. Jiang, Y. Mei, H.L. Luo and C. Politis

Summary: The authors have concentrated on the effect of Pb on the superconducting properties of the Bi-Sr-Ca-Cu-O system. Preliminary results are also presented on the effect of varying the Sr:Ca and Bi:Ca ratios in Pb-substituted samples. It is shown that the addition of Pb does not guarantee a step-free resistive transition. The steps in the resistivity become more pronounced as the Bi:Ca ratio is increased. This gradual, systematic change suggests that the reduced continuity is not the result of an abrupt reduction in the c-spacing near grain boundaries as observed in Pb-free samples.
Preparation of high-T/sub c/ superconducting thick films and power conducting tubes by a low-pressure plasma spraying

   K. Tachikawa, M. Ono, Y. Shinbo, T. Suzuki, M. Kabasawa and S. Kosuge

Summary: Superconducting thick films of YBaCuO and BiSrCaCuO systems have been prepared using a low-pressure plasma spraying technique. The chemical composition of the deposits was very close to that of the spraying powders. After postannealing the films showed zero resistance temperatures, T/sub c/ of approximately 90 K for YBaCuO and approximately 60 K for BiSrCaCuO. Superconducting power tubes were successfully produced by a low-pressure plasma spraying. 100-200- mu m-thick YBaCuO superconducting films were deposited on the outer surface of the Ni-plated Cu tubes. After postannealing at 930 degrees C for 1 h the films exhibited T/sub c/ of 85-90 K. An improved film preparation process in which a flux layer is coated on the Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub x/ matrix layer by a low-pressure plasma spraying has been developed. Enhanced critical currents have been achieved by this process.
Round robin tests of T/sub c/ and I/sub c/ on YBa/sub 2/Cu/sub 3/O/sub x/

   Y. Kimura, N. Higuchi, S. Meguro, K. Takahashi, K. Uyeda, T. Ishihara, E. Inukai and M. Umeda

Summary: Methods for measuring the critical properties such as critical temperature and critical current were investigated and studied by round robin tests. The investigation was carried out in five steps: (1) decision on the specifications of common samples and measuring methods; (2) preparation and characterization of common samples; (3) distribution of samples to ten member research organizations; (4) experimental measurement at the respective research organizations; and (5) analysis of measurement results. The measurement of critical temperature and critical current were made mainly by the four-probe methods and partially by the magnetization method. The results were found to disperse, depending on the measurement methods and definitions of T/sub c/ and I/sub c/.
Relation of the N-value of the resistive transition to microstructure and inhomogeneity for YBa/sub 2/Cu/sub 3/O/sub 7/ wires

   J.E. Evetts, B.A. Glowacki, P.L. Sampson, M.G. Blamire, N.M. Alford and M.A. Harmer

Summary: Measurements are reported of resistive transitions at 77 K for a series of YBa/sub 2/Cu/sub 3/O/sub 7/ wires as a function of applied magnetic field. The transitions are very broad and for electric fields in the range 10/sup -6/ to 10/sup -3/ V m/sup -1/ can be fitted approximately by a power law with n-values in the range 4-60. The n-value is observed to fall with increasing applied magnetic field and shows strong hysteresis related to trapped flux when the field is cycled. The variation of both critical current and n-value with applied field is related to the microstructure of wires with different additives, and on a series of wires of different bulk density prepared using viscous processing techniques. Extensions to the analysis for conventional composites makes it possible to relate the n-value to the statistical critical current distribution.
Deterioration mechanism of oxide superconductor

   K. Imai and H. Matsuba

Summary: Deterioration of oxide superconductors has been investigated by evaluating the critical current densities, J/sub c/, at 77 K and the conductivity at room temperature. The oxide superconductors were exposed to both moisture and heat cycles. The authors observed slow decreases in J/sub c/ often followed by fast decreases. The experimental results indicate that an external substance penetrates into the superconductors and brings about chemical reactions to form nonsuperconducting products so that volume expansion occurs at the site causing cracks.
Low resistance ohmic contacts to high-T/sub c/ superconducting thin films

   Y. Tazoh, K. Aihara, K. Miyabara, K. Hohkawa and M. Oshima

Summary: Metal contacts to high-T/sub c/ superconducting thin films have been studied. By analyzing the I-V characteristics at contact junctions and by synchrotron radiation photoemission spectroscopy, the effect of contact metal and surface treatment before depositing contact metal on the metal-superconductor interface characteristics has been investigated. Low-resistance ohmic contacts are realized by the following sequence of processes: (1) oxygen ion sputter etching; (2) high-pressure oxygen plasma treatment, and (3) in situ deposition of Au with no interfacial reaction with the superconductor. A low-contact resistivity equal to 5.5*10/sup -7/ Omega -cm/sup 2/ at 77 K is realized experimentally.
Low contact-resistivity junctions to ceramic superconductors

   M.P. Maley, J.O. Willis, J.D. Katz, R.G. Castro and R.M. Aikin

Summary: A report is presented on the development of a plasma-arc spray process for the application of low-resistivity silver contact junctions onto YBa/sub 2/Cu/sub 3/O/sub 7/ sintered ceramic materials. The contact resistances decrease montonically with decreasing temperature and are typically approximately 10/sup -8/ Omega -cm/sup 2/ at 75 K. I-V characteristics are linear up to a critical current density that agrees with that of the underlying superconducting material. Advantages over other contact methods include ease of application, absence of any postprocessing treatment, and applicability to large areas and arbitrary shapes.
Ag screen contacts to sintered YBa/sub 2/Cu/sub 3/O/sub x/ powder for rapid superconductor characterization

   J. Moreland and L.F. Goodrich

Summary: The authors have developed a method for making current contacts and voltage taps to YBa/sub 2/Cu/sub 3/O/sub x/ sintered pellets for rapid superconductor characterization. Ag wire screens are interleaved between calcined powder sections and then fired at 930 degrees C to form a composite pellet for resistivity and critical current measurements. The Ag diffuses into the powder during the sintering process forming a proximity contact that is permeable to O/sub 2/. Contact surface resistivities (area-resistance product) range from 1 to 10 mu Omega -cm/sup 2/ at 77 K for the Ag-powder interface. In this configuration, current can be uniformly injected into the ends of the pellet through the bonded Ag screen electrodes. Ag screen voltage contacts, which span a cross section of the pellet, may provide an ideal geometry for detecting voltage drops along the pellet, minimizing current transfer effects.
Experimental study of flux pinning in NbN films and multilayers: ultimate limits on critical currents in superconductors

   K.E. Gray, R.T. Kampwirth, D.W. Capone II and J.M. Murdock

Summary: A flux-pinning model is presented which predicts the maximum critical current density attainable in superconductors. That such a limit must exist comes from the realization that flux pinning is strongest in regions of weak superconductivity, but these regions cannot carry a large supercurrent. Since the same regions within the superconductor cannot be used for both pinning and supercurrent conduction, there must be an optimum mix, leading to a maximum J/sub c/. Measurements on films and multilayers of NbN have verified many details of the model including anisotropy effects and a strong reduction in J/sub c/ for defect spacings smaller than the flux core diameter. In an optimized multilayer the pinning force reached approximately 22% of the theoretical maximum. The implications of these results on the practical applications of NbN films and on the maximum critical current density in the high-temperature oxide superconductors are also discussed.
Effects of additive elements on continuous ultra-fine Nb/sub 3/Al MF superconductor

   T. Takeuchi, Y. Iijima, M. Kosuge, T. Kuroda, M. Yuyama and K. Inoue

Summary: Nb/sub 3/Al multifilamentary (MF) wire can be fabricated by the composite process using various Al-based alloy cores and pure Nb matrix. Additive elements of Mg, Ag, Cu and Zn harden the Al core preferentially and then improve the workability of the Nb/Al composite, permitting it to be cold-drawn into a wire with ultrafine Al-based alloy filaments (filament number: 1.8 million, diameter: about 0.1 mu m). Reacted wires at 700-900 degrees C show T/sub c/ of 15-16 K, mu /sub 0/H/sub c2/ (4.2 K) of 21-22 T and J/sub c/ (4.2 K, 10 T) of 1-1.5*10/sup 9/ A/m/sup 2/. A two-stage reaction consisting of a reaction above 950 degrees C and a subsequent reaction around 700 degrees C is carried out to improve critical values; T/sub c/ and mu /sub 0/H/sub c2/ are increased to 17.4 K and 25.4 T, respectively. Excellent superconducting properties involving good strain tolerance ( epsilon /sub irrev/=1.3%) indicate that this Nb/sub 3/Al is very promising for practical high-field superconducting cables.
Local pinning-force distribution in NbN films

   A. Pruymboom, W.H.B. Hoondert and P.H. Kes

Summary: The authors performed measurements of the flux-flow resistivity on a thin film of NbN. By fitting the resistivity, measured as a function of the current, to a theoretical expression, they were able to obtain the distribution function of local depinning forces in the film. It appears that the distribution is very broad and that only a minor fraction of flux lines is flowing at what is usually defined as J/sub c/. These observations are in agreement with the results of the pinning-force measurements. The measurements reveal that at high fields pinning is limited by flux-line shear and that the effective channel width for shear is equal to the flux-line spacing. They suggest that variations of the local depinning force on various length scales always allow the flow of single rows of flux lines.
Neutron irradiation of sputtered NbN films

   H.W. Weber, P. Gregshammer, K.E. Gray and R.T. Kampwirth

Summary: The authors report neutron irradiation experiments on sputtered NbN films, up to a fluence of 10/sup 23/ m/sup -2/ (E> 0.1 MeV), which prove that NbN films are also extremely radiation-hard high-field superconductors. Both the transition temperatures, T/sub c/, and the normal state resistivities show only small changes with neutron fluence. Concerning the critical current densities, j/sub c/, degradations by as much as 30% are observed at low fields, whereas in an intermediate field range (11-15 T), virtually no change of j/sub c/ is seen, and at high fields (near 20 T), even an increase of j/sub c/ is found. The latter observation is ascribed to a radiation-induced increase of the upper critical field, B/sub c2/, and to the occurrence of peak effects near B/sub c2/.
Process control for the low temperature deposition of niobium-nitride thin films

   A.C. Anderson, D.J. Lichtenwalner and W.T. Brogan

Summary: The authors investigated the process of DC and RF magnetron reactive sputtering of NbN with the purpose of clarifying the issues which are important for process control. Based on a simple physical model of the deposition process, parameters (plasma impedance and plasma concentration of reactive species) have been selected for study and their effects on the properties of the films (transition temperature, room temperature resistance, and RF surface impedance) have been evaluated experimentally. Based on these experiments, a simple feedback scheme using the plasma impedance as a control parameter was implemented, allowing for the consistent deposition of high-quality films. The same scheme can be used for the control of the stoichiometry of any reactive sputtering process, including the deposition of the high-transition-temperature oxide films.
Fabrication of multifilamentary Nb/sub 3/(Al,Ge) wires through a modified jelly roll process

   K. Tachikawa, Y. Kamisada and E. Suzuki

Summary: Nb/Al-Ge alloy composites were fabricated into multifilamentary wires through a modified jelly roll (MJR) process. A Nb mesh sheet was used as the Nb component. An Al-Ge alloy prepared by a conventional casting process was forged and rolled into a sheet of 0.2 mm in thickness. The Nb/Al-Ge composite was prepared by wrapping the Nb mesh sheet together with the Al-Ge alloy sheet around a Nb core into a jelly-roll form. The MJR composite was encased in a Cu-Ni alloy tube of which the outer diameter was 43 mm. The resulting composite was hydrostatically pressed and extruded into a rod of 18 mm in diameter. A Nb barrier was then inserted between the MJR and the Cu-Ni jacket. The composite rod was swaged and drawn into a wire without any intermediate annealing. The wire was able to be drawn down to a very small diameter of 0.1 mm. The cross-sectional configuration of the MJR composite was not much disturbed by the fabrication. An onset T/sub c/ of 19.3 K has been achieved.
Reaction kinetics of phase formation in Nb-Al powder metallurgy processed wire

   K.R. Coffey, K. Barmak, D.A. Rudman, C.L.H. Thieme and S. Foner

Summary: The sequence of phases formed in the low-temperature reaction of niobium and aluminium to form the A15 superconductor, Nb/sub 3/Al, was studied in high areal reduction powder metallurgy processed wire samples. The reaction path observed was the same as that reported previously for multilayer Nb/Al thin films. The reaction proceeds without the formation of the sigma phase, Nb/sub 2/Al resulting in a metastable A15 of higher Al concentration. The extent of this metastable extension is estimated to be 22-24 at.% Al, based on the resistive T/sub c/ of 17.0 K observed. The reaction kinetics of the wire samples were examined by scanning heat flux calorimetry, and the activation energy of A15 formation was found to be 3.1 eV. The formation of NbAl/sub 3/ and dissolution of Al into the Nb lattice were both observed as precursor reactions with much lower activation energies.
Normal state resistance and low temperature magnetoresistance of superconducting cables for accelerator magnets

   W.B. Sampson, M. Garber and A.K. Ghosh

Summary: Resistance measurements which are routinely made on superconducting wires and cables for accelerator magnets can provide an accurate measure of the copper-to-superconductor ratio. Compared to the etch and weight technique, a resistance specification for Cu/Sc is preferable for monitoring of this parameter during wire and cable production. Results shown here indicate that by using the 4 K magnetoresistance data of bulk copper and the size effect formula for the resistivity enhancement of copper, the measured residual resistance ratio can be used to estimate the resistance at high fields.
Losses in superconducting wires with inhomogeneous and anisotropic matrix conductivity over cross section

   E.N. Aksenova

Summary: Methods of calculating energy losses for multifilamentary wires with anisotropic and inhomogeneous conductivity of a matrix over the cross section are developed, in particular, for wires with a cluster assembly. Analysis of diffusion of the magnetic flux and dissipative characteristics for the multifilamentary wire in the transverse AC magnetic field shows that: (1) in the case of the matrix anisotropic conductivity the processes of current coupling are antiparallel, making a contribution to losses, which is proportional to one of the matrix components, sigma /sub 1/; (2) the presence of the matrix conductivity inhomogeneity causes peculiarities in the saturation process, namely, that the longitudinal-to-the-filaments electric field has local maxima at the outer and the inner radii; (3) this circumstance explains the process of parallel saturation of groups of filaments and the wire as a whole, taking place in the wire with cluster assembly; and (4) the rise of the ratio of hysteresis losses to the filament diameter with decrease of the latter for diameter approximately 1 mu m can be accounted for by the cluster saturation and increase of filament inhomogeneity in their thinning without recourse to the proximity effect.
AC losses of NbTi superconducting wires with fine filament

   K. Ohmatsu, M. Nagata, M. Kawashima, H. Tateishi and T. Onishi

Summary: An investigation was conducted of the AC losses in coils with NbTi superconducting wires. The authors used the multiple-stacking procedure to prepare the wires, which varied in filament size from 10 mu m to 0.07 mu m. Three kinds of wires with 0.07- mu m filament were specially fabricated to estimate the proximity effect on AC losses. The distances between the filaments of these wires were 21 nm, 42 nm, and 70 nm, respectively. AC losses were measured for small coils at 60 Hz. The proximity effect was observed for the wires with 0.07- mu m filament when the distance was 21 nm. Conversely, when the distance was 42 nm, the loss decreased to the small value of 11 kW/m/sup 3/ at 0.5 T and 4.2 K.
Initiation of flux jump in SC composite by heat pulse

   E.Y. Klimenko and N.N. Martovetsky

Summary: Nonisothermal diffusion of magnetic flux after a heat pulse shot on the surface of SC (superconductor) composite has been studied numerically taking into account the smoothed transition characteristic of the SC. It is shown that for an SC composite with poor stabilization, the current and heat redistribution change significantly the estimations of stability based on steady-state functions of heat generation and heat transfer. The critical pulsed energy strongly depends on the initial current distribution over the conductor cross section, and the energy may be much less for a conductor with growing current than for a conductor with the same current in steady state. It has been found that undercritical heat pulses only slightly affect current density profile, but stability increases as time delay increases between the current input halt and the pulse shot. It has also been found that for a SC composite with poor stabilization, the transverse thermal conductivity is more important than the electrical resistivity of the matrix from the stability standpoint.
Simplified loss expressions for superconductors carrying DC transport current in an AC field

   J.V. Minervini

Summary: Simplified expressions are reported for the shielding and transport loss components as a function of the applied transverse field and the transport current. These expressions are based on a numerical solution but are approximated by analytic expressions in such a way that they are as simple to use as the equivalent expressions derived from the one-dimensional slab model. A comparison of the two models is presented.
Study of serviceability of superconducting wires at 50-Hz frequency

   E.N. Aksenova, P.V. Aksenov, V.S. Kruglov, G.K. Zelensky and E.V. Nikulenkov

Summary: A stationary equation for thermal conductivity is solved for a multifilamentary superconducting wire in the AC external magnetic field with an in-phase varying transport current of the amplitude j/sub m/<
Calculating the J/sub c/, B, T surface for niobium titanium using a reduced-state model

   M.A. Green

Summary: A method is presented for calculating the J/sub c/, B, T surface for commercial niobium titanium superconductor given T/sub c/, B/sub c2/ and J/sub c/ over a range B at a given temperature. The J/sub c/ calculated as a function of B and T agrees with measured values of J/sub c/ quite well over a range of T from 1.5 K to 7 K and a range of B from 0.1 T to 10 T. The values of J/sub c/ given by this theory are good enough to be used to calculate the performance of superconducting magnets at temperatures other than 4.2 K, and the theory can be used to predict the magnetization effects of superconductors over a wide range of temperatures and inductions.
Temperature dependence of penetration depth in thin film niobium

   N. More, B. Muhlfelder and J. Lockhart

Summary: A novel technique is presented which should allow precise determination of the temperature dependence of the inductance, and hence of the penetration depth, of superconducting niobium thin-film structures. Four niobium thin-film stripline inductors are arranged in a bridge configuration, and inductance differences are measured using a potentiometric technique with a SQUID (superconducting quantum interference device) as the null detector. Numerical simulations of the stripline inductances are presented which allow the performance of the measurement technique to be evaluated. The prediction of the two-fluid model for the penetration-depth temperature dependence is given for reduced temperatures of 0.3 to 0.9. The experimental apparatus and its resolution and accuracy are discussed.
Current distribution and AC losses in twisted multifilamentary AC superconductors

   A.J.M. Roovers and L.J.M. van de Klundert

Summary: The development of AC superconductors has led to multifilamentary wires having a highly resistive matrix material and a small twist pitch and filament diameter. A numerical one-dimensional model is presented which enables the authors to calculate the current distribution as well as the magnetization and transport current loss in a current-carrying AC superconductor subjected to a transverse alternating magnetic field. The impact on wire design is also discussed.
Numerical solution of the transverse resistivity of superconducting cables under AC conditions

   R.A. Hartmann, D. Dijkstra, F.P.H. van Beckum and L.J.M. van de Klundert

Summary: The authors develop a numerical method for calculating the transverse resistivity of superconducting cables. A superconducting cable consists of a twisted bundle of strands with a nonconducting inner region. If such a cable is placed in an external magnetic field, the induced currents will not merely flow in the axial direction, but also around the center, in the plane of the cross section. It is shown that the transverse transport current, which is induced by external fields acting on the cable, can saturate most of the filaments of the superconducting layer. This results in a smaller maximal value of a longitudinal transport current and small coupling losses.
Formation of metal/superconducting oxide composites by oxidation of melt spun metallic precursors

   H. Hsu, L. Masur, C. Joshi, K. Sandhage, W. Carter and G.J. Yurek

Summary: Melt spinning was used to produce homogeneous, melt-spun ribbons of Yb/sub 1/Ba/sub 2/Cu/sub 3/ and Yb/sub 1/Ba/sub 2/Cu/sub 3/ plus various amounts of Ag. While none of these alloys was completely glassy, they did contain glassy alloy and they were homogeneous. Metallic precursors as long as 12 m were produced; the widths were typically 1 to 2 mm, and the thicknesses ranged from 25 to 170 mu m. The dimensions of the specimens varied with the alloy composition and the processing conditions.
Critical current densities for the high temperature ceramic superconductors YBa/sub 2/Cu/sub 3/O/sub 7/ and Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10+ delta /

   W.C. McGinnis, T.E. Jones, E.W. Jacobs, R.D. Boss and J.W. Schindler

Summary: A pulsed transport technique has been used to measure the zero-field critical current densities of YBa/sub 2/Cu/sub 3/O/sub 7/ ceramic superconductors prepared under different sintering conditions. This low duty-cycle, pulsed technique, used on specially prepared samples with low-resistance current contacts, allows one to determine the entire superconducting/normal phase boundary without the problems associated with sample heating. The results can be interpreted in terms of two different critical-current densities. The intergrain critical current is low and is limited by the weak links between the grains; the intrinsic intragrain critical current is greater than 10/sup 4/ A/cm/sup 2/ at 77 K. Critical-current values inferred from magnetic hysteresis measurements made on the same samples agree with the intrinsic intragrain critical currents obtained using the pulsed transport technique. In addition, the magnetization-derived critical-current density has been determined for the high T/sub c/ phase Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10+ delta / at 77 K.
Size effects in the magnetisation of high T/sub c/ powders

   A.D. Hibbs and A.M. Campbell

Summary: The critical-current and flux profile within a series of different size powders of YBa/sub 2/Cu/sub 3/O/sub 7/ has been measured. At zero field, supercurrents flow unimpeded within the grains. However, for fields above 100 mT, it appears that the grains are subdivided on a scale smaller than 1 mu m. Using this interpretation it is found that the interaction of the fluxoids with the pinning centers is very similar to that taking place in V/sub 3/Si and commercial NbTi.
Flux trapping and magnetisation of hollow superconducting cylinders

   F.J. Eberhardt, A.D. Hibbs and A.M. Campbell

Summary: The magnetisation of hollow cylinders of high T/sub c/ materials and the field trapped inside them have been measured by integrating the signal from coils outside and inside the cylinders. The two coils allow the field trapped in the grains themselves to be separated from the field due to the circulating currents in the bulk material. The trapped field indicates the maximum field that can be expected in a magnet. For practical purposes the most important parameter is the field at which J/sub c/ drops to half its zero-field value. Cylinders have been made from yttrium-barium-copper oxide and from bismuth-strontium-calcium-copper oxide. Various preparation methods have been used.
High-T/sub c/ superconducting glass ceramics based on the Bi-Ca-Sr-Cu-O system

   T. Komatsu, R. Sato, K. Imai, K. Matusita and T. Yamashita

Summary: Various high-T/sub c/ superconducting glass ceramics based on the Bi-Ca-Sr-Cu-O system were prepared by the melt-quenching method. The melt-quenched sample of Bi/sub 1.2/CaSrCu/sub 2/O/sub x/ was found to be a glass that became a high-T/sub c/ superconductor with T/sub c/ (zero)=85 K by annealing at 820 degrees C. The Bi/sub 1-x/Pb/sub x/CaSrCu/sub 2/O/sub y/ glasses also became high-T/sub c/ superconductors upon annealing at temperatures above 800 degrees C. The glass ceramics of Bi/sub 0.9/Pb/sub 0.1/CaSrCu/sub 2/O/sub x/ exhibited superconductivity with T/sub c/ (onset)=116 and T/sub c/ (zero)=100 K.
Superconductivity and crystal structure in the Bi-Pb-Sr-Ca-Cu-O system

   Xing Zhu, Sungi Feng, Jian Zhang and Zizhao Gan

Summary: BiPbSrCaCuO superconductors with various nominal compositions have been studied. T/sub c,zer0/=111 K and an AC Meissner effect of 93.1% have been obtained in a (Bi/sub 0.8/Pb/sub 0.2/)/sub 2/Sr/sub 2/Ca/sub 2/-Cu/sub 3/O/sub x/ sample. The authors have also synthesized a single-phase (Bi/sub 0.8/Pb/sub 0.2/)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ sample. The crystal structure of the superconducting phase has been determined by transmission electron microscopy, convergent beam electron diffraction, and powder X-ray diffraction. The crystal structure of the Pb-doped system has a tetragonal unit cell (a=b=3.823 AA, c=37.074 AA), space group I4/MMM. The atomic coordinates have been determined. Unlike the Bi-based system without Pb, the Pb-doped 2223 phase has very weak or no modulation structure, which in turn changes the symmetry from pseudo-tetragonal to tetragonal. The relationship between synthesis conditions and superconductivity is discussed.
Effect of synthesis condition on superconducting transmission temperature in Tl-Ba-Ca-Cu-O system

   Liu Chunfang, Zhou Lian, Yang Zhaoling, Wang Shugian, Du Shejun, Xiu Jingren and Ye Yongcai

Summary: The formation of the high-T/sub c/ superconducting phases in the Tl-Ba-Ca-Cu-O system has been investigated. Stable superconductivity up to 119 K was observed. One of the superconducting phases displays an onset temperature of 122 K. The resistance of the TlBaCaCu/sub 2/O/sub y/ sample, which is almost single-phase, starts to drop sharply above 113 K and reaches zero at 108 K. The bulk samples with different compositions in the Tl-Ba-Ca-Cu-O system were synthesized. The electrical resistivity and AC magnetic susceptibility dependence on the temperature show that the zero-resistance transition temperature in most of the samples is above 96 K.
Promoting effects of steam on the sintering process of YBCO ceramic superconductors

   S.T. Chen, X.S. Li, F.C. Yin and X. Yao

Summary: The effects of steam on the sintering of Y-Ba-Cu-O (YBCO) ceramic superconductors are reported. It has been found that steam is favourable for promoting the sintering of YBCO ceramics and increasing the bulk density of the material as well as the critical-current density. The linear contraction coefficient increases with increasing steam pressure. The samples of YBCO made by this method have shown good resistance against H/sub 2/O and CO/sub 2/. The reason why steam promotes the sintering process is explained.
Studies on the non rare earth oxide superconductors fabricated by sintering

   H. Sekine, K. Inoue, H. Maeda, K. Numata, K. Mori and H. Yamamoto

Summary: Wire, tape, and bulk specimens of Bi-(Pb)-Sr-Ca-Cu-O material have been prepared. Studies on the superconducting properties and metallurgical studies have been conducted. The results of thermogravimetric analysis indicate that the phase transformation which accompanies absorption of oxygen does not occur in this material from 860 degrees C down to 400 degrees C. Tape specimens prepared by a combination of cold work and sintering showed J/sub c/ of 1100 A/cm/sup 2/ at 77 K with a good reproducibility. In these tape specimens, the c-axis of the grains tends to align perpendicularly to the tape surface. A 1330-filament Bi-Pb-Sr-Ca-Cu-O wire with a Ag matrix has been fabricated, showing high-T/sub c/ transitions when sintered at relatively low temperature. The concentration of Pb in the oxide must be controlled (reduced) before packing into an Ag sheath for the superconducting phase to be formed in a long wire. The results of this study indicate that the Bi-Sr-Ca-Cu-O system material has several favorable features which could make practical use of this material possible.
The manufacturing process and properties of the high T/sub c/ oxide superconducting wire

   M. Kawashima, M. Nagata, Y. Hosoda, S. Takano, N. Shibuta, H. Mukai and T. Hikata

Summary: The critical-current densities (J/sub c/) of Ag-sheathed tapes of oxide superconductors were investigated using both the yttrium and bismuth systems. Using a press process for Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/, BiSrCaCu/sub 2/O/sub x/, and Bi/sub 0.8/Pb/sub 0.2/SrCaCu/sub 2/O/sub x/, increases in J/sub c/ were inconsistently observed. J/sub c/ showed an increase for Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ but not for BiSrCaCu/sub 2/O/sub x/. The Bi/sub 0.8/Pb/sub 0.2/SrCaCu/sub 2/O/sub x/ superconductor also showed increased J/sub c/. The press processing improved the superconducting properties of Ag-sheathed wire not only for J/sub c/ but also for T/sub c/. The authors obtained high T/sub c/ phase T/sub c(R=zero)/=104 K and J/sub c/=1850 A/cm/sup 2/ for Bi/sub 0.8/Pb/sub 0.2/SrCaCu/sub 2/O/sub x/ superconductor.
Oxygen kinetics and superconductivity in the high-T/sub c/ oxide YBa/sub 2/Cu/sub 3/O/sub x/

   O.F. de Lima, R.F. Jardim, S. Gama and I. Torriani

Summary: Disk-shaped samples of the nominal compositions YBa/sub 2/Cu/sub 3/O/sub 7/, Y/sub 2/BaCuO/sub 5/ and BaCuO/sub 2/ were initially produced through the solid diffusion method. These samples were then cut into several small pieces, which were used for oxygen intercalation and desorption studies for temperatures between 330 degrees C and 700 degrees C. The compound YBa/sub 2/Cu/sub 3/O/sub x/ went through a gradual transformation, going from the pure superconducting orthorhombic phase (x=7.0) to the pure semiconducting tetragonal phase (x=6.3). The compound BaCuO/sub y/ also varied its oxygen content, in the range 2.00
Compacted 1-2-3 ceramic powders treated as superconducting composites

   E.W. Collings, A.J. Markworth and K.R. Marken Jr.

Summary: Magnetization studies of closely spaced fine-filamentary Cu/NbTi composites have shown that, at very low applied field strengths, proximity-effect coupling (across the Cu matrix) between the filaments causes the assembly to exclude flux in the manner of a solid block of superconductor of the same outside diameter as the filamentary bundle. Then at somewhat higher applied field strengths (but still with H
Critical current density of Y-Ba-Cu oxide superconductor prepared by a diffusion process

   N. Sadakata, M. Sugimoto, O. Kohno and K. Tachikawa

Summary: The formation of the YBa/sub 2/Cu/sub 3/O/sub 7-y/ layer has been investigated by a diffusion process as basic research for high-T/sub c/ superconductor fabrication. The starting materials were Y/sub 2/BaCuO/sub 5/ and barium cuprate. A dense layer of YBa/sub 2/Cu/sub 3/O/sub 7-y/ was formed on a Y/sub 2/BaCuO/sub 5/ substrate, and the starting barium cuprate layer was fully converted to the superconducting oxide. X-ray diffractometry revealed that the layer consisted of an orthorhombic crystal structure. The reacted specimens showed good superconductivity. A zero-resistance temperature of 91.5 K and a critical-current density of 1900 A/cm/sup 2/ (77 K, 0 T) were achieved in the layer. Preparation conditions and superconducting properties, particularly J/sub c/ characteristics, are investigated. The diffusion phenomena that result in the formation of the YBa/sub 2/Cu/sub 3/O/sub 7-y/ phase by this process are also discussed.
Grain size control in powder processed Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub x/

   K. No, J.D. Verhoeven, R.W. McCallum and E.D. Gison

Summary: It is demonstrated that small grained YBa2Cu30x (123) material can be made from powders of Y2O3, BaC03 and CuO by avoiding liquid phase formation in the high temperature treatments. Techniques for avoiding liquid phase formation are demonstrated and transport Jc measurements versus grain size are presented .
Synthesis of a high T/sub c/ superconducting phase in Bi-Sr-Ca-Cu-O system

   S. Miyashita, M. Wakata, A. Nozaki, K. Egawa, T. Ogama and K. Yoshizaki

Summary: The synthesis of a high-T/sub c/ phase in the Bi-Sr-Ca-Cu-O system by the solid-state reaction and the J/sub c/ characteristics are reported. The partial pressure of oxygen near 0.1 atm is preferable as a sintering atmosphere, and Pb addition is effective to produce a large amount of high-T/sub c/ phase. Two classes of amorphouslike metastable superconducting phases with T/sub c/ of approximately 90 K and approximately 40 K, respectively, are found. It is thought that they have a randomly stacked structure. J/sub c/ of 93 A/cm/sup 2/ at zero field, 77 K is obtained for the sample with T/sub c/( rho =0)=107 K, which includes a high-T/sub c/ phase and a small amount of a low-T/sub c/ phase covered with the former phase. J/sub c/ is exponentially decreased by increasing the field. It is found that the transport J/sub c/ is limited by the weak-link regions in this system, as evidenced by the observation of a low resistive state above the J/sub c/ and of superconductivity in that state.
Composite core Nb/sub 3/Sn wires: preparation and characterization

   R. Flukiger, W. Specking, M. Klemm and S. Gauss

Summary: Powder metallurgically processed composite-core Nb/sub 3/Sn wires, a novel type with filaments containing controlled amounts of normal conducting inclusions elongated in the wire axis, e.g., Ta or NbTi, have recently been developed. Composite cores replace the Nb cores, which are inserted either in a CuSn or in a Cu matrix for producing wires by the bronze route or by the internal Sn diffusion process, respectively. The ductile inclusions are deformed during the wire drawing process to long ribbons being <100 nm apart. If the reaction temperature is sufficiently low, the Ta or NbTi shows little reaction with the Nb/sub 3/Sn phase but reduces the A15 grain growth in the radial direction. The resulting enhanced pinning at the grain boundaries (artificial pinning) leads to higher critical-current densities, particularly in the field range B<14 T. A difference between the observed field dependence for Ta and NbTi inclusions in the present configuration is explained by different degrees of prestress. The achievement of higher J/sub c/ values at 10-12 T may be advantageous for their application in fusion magnets.
Influence of cyclic pumped diffusion on the morphology and microstructure of A15 layers in bronze processed multifilamentary wire

   B.A. Glowacki and J.E. Evetts

Summary: The authors have used a novel reaction method called cyclic-pumped diffusion (CPD) to achieve near uniform A15 reaction layers on filaments throughout the cross-section of a multifilamentary composite. A detailed investigation of the spatial variation of the lattice parameter during reaction in filaments and in the bronze matrix has enabled them to optimize the time and temperature for successive reaction cycles. A 61*61 filament Nb-7.5% wt Ta-bronze composite reacted using CPD in the range 600-800 degrees C shows a compound thickness variation between the inner and outer filaments of approximately 30%, while the same composite given a conventional isothermal heat treatment at 700 degrees C shows a corresponding layer thickness variation of approximately 200%. The consequences of the CPD reaction method for the design of composites containing tin reservoirs are discussed.
Low loss and high current Nb/sub 3/Sn conductors made by the internal-tin method

   H.C. Kanithi, L.R. Motowidlo, G.M. Ozeryansky, D.W. Hazelton and B.A. Zeitlin

Summary: Upon reaction heat treatment of Nb/sub 3/Sn-type conductors, niobium filaments grow in size due to a volume expansion. In conductors made by the internal-tin method, the filaments are generally closer to each other than in the bronze-route conductors. This can lead to filament bridging after the reaction heat treatment. For magnet applications such as in fusion and high-energy physics where AC losses have to be limited, the authors have designed and fabricated conductors with sufficiently large filament separation. The conductors incorporate tantalum as a diffusion barrier. An outline is given of the manufacturing process, with details of significant design parameters. Required heat-treatment conditions are addressed. Critical-current performance and AC loss characteristics are presented and compared to those of other internal-tin processed conductors.
Ductility enhancement in unreacted internal-Sn Nb/sub 3/Sn through low-temperature anneals

   M.J. Strum, L.T. Summers and J.R. Miller

Summary: It is shown that a lack of tensile ductility in as-drawn superconducting wires at room temperature can lead to damage during magnet fabrication steps such as cabling and coil winding. The tensile elongation of 0.42 mm internal-Sn Nb/sub 3/Sn conductor in the as-drawn unreacted condition is limited to less than 3% at room temperature. The tensile elongation is substantially enhanced through low-temperature annealing treatments at 200 degrees C, increasing to as high as 10% after 24 h at 200 degrees C. This effect is attributed to increased work hardening capacity from softening, which reduces yield strengths up to 50% while maintaining 90% of the tensile strength. Fracture surfaces of annealed wires reveal increased adhesion between the Sn cores and the surrounding Cu as well as an increase in ductile void coalescence as the failure mechanism within the Cu. Preliminary results on the prereaction strain sensitivity of reacted wire critical currents confirm the increased strain tolerance in annealed wires.
Metallurgy and superconductivity in bronze-processed Nb/sub 3/Sn doped cerium and cerium-titanium

   Liu Chunfang, Zhou Lian and Yang Zhaoling

Summary: Metallurgy and superconductivity in Ce-doped and Ce-Ti-doped Nb/sub 3/Sn samples were investigated. The wires containing Ce-bronze and Ce-Te-bronze were not noticeably difficult to draw. The addition of Ce to the bronze not only enhances the growth rate of the Nb/sub 3/Sn layer but also improves the composition distribution within the wire. The critical temperature T/sub c/ of Ce-doped samples treated at 700 degrees C is obviously higher than that of pure Nb/sub 3/Sn. The J/sub c/ difference between samples with small amounts of Ce and pure Nb/sub 3/Sn is not obvious. J/sub c/ decreases slightly in low field with increasing Ce content.
Internal tin-Nb/sub 3/Sn composite

   S. Hong, D. Geschwindner, A. Mantone, W. Marancik and R. Zhou

Summary: Investigations are conducted of Nb/sub 3/Sn multifilamentry composite fabrication by the internal-tin method. One method is to distribute tin around each filament uniformly, and the other approach is to distribute tin semiuniformly. The authors report the preliminary performance results for these two composites.
YBa/sub 2/Cu/sub 3/O/sub 7/ thin films grown by high pressure reactive evaporation and high pressure reactive sputtering

   D.K. Lathrop, S.E. Russek, K. Tanabe and R.A. Buhrman

Summary: A high-pressure reactive evaporation process and a high-pressure reactive sputtering process have been developed for the growth of high-quality thin films of YBa/sub 2/Cu/sub 3/O/sub 7/. Both techniques, when used with heated substrates, are effective in the formation of the 123 phase in situ during the film growth. With reactive evaporation only a cooldown anneal in a higher-pressure oxygen ambient is necessary to obtain good superconducting properties. For the reactive sputtering process, a brief, postgrowth, rapid thermal anneal step is required for best results. Fully epitaxial growth has been achieved with single-crystal MgO substrates. The resultant films, which can be quite smooth and uniform, have been patterned to micron and submicron dimensions, and the transport properties of these microstructures have been examined.
Superconducting properties of magnetron sputtered high T/sub c/ thin films containing oxide compounds of yttrium, bismuth, or thallium

   J.H. Kang, R.T. Kampwirth and K.E. Gray

Summary: The authors have used multiple-source magnetron sputtering to prepare thin films of Y-Ba-Cu-O, Bi-Ca-Sr-Cu-O, and Tl-Ca-Ba-Cu-O on
Electronic noise in Ba/sub 2/YCu/sub 3/O/sub 7/ films at high temperatures: a possible connection to stress relaxation

   A. Davidson, N.F. Pedersen, A. Palevski and M.R. Scheuermann

Summary: Two types of electronic noise have been observed in Ba/sub 2/YCu/sub 3/O/sub 7/ at high temperature. One type is probably due to temperature and pressure fluctuations in the environment of the sample. Because of the known sensitivity of Ba/sub 2/YCu/sub 3/O/sub 7/ resistance to both temperature and pressure, this mechanism translates into 10 to 100 nV per root Hz of noise at temperatures above 750 K. The second type is more intrinsic, and may be related to stress relaxation in the film induced by the structural changes associated with the orthorhombic-tetragonal transition near 950 K.
Inductive measurements of critical current density in superconducting thin films

   J.H. Claassen

Summary: A noncontacting method of probing the current-induced breakdown of superconductivity (i.e., J/sub c/) in thin films is described which makes use of a single pancake coil pressed against the film surface. The technique has a sensitivity that is approximately 100 times greater than direct transport measurements using room-temperature electronics, and it eliminates many of the attendant difficulties of the latter. Preliminary results on Nb and Y-Ba-Cu-O films at 4.2 K reveal an exponential voltage-current dependence, as expected from the activated flux creep model. It is noted that, this being the case, no unique critical-current density can be defined. In the case of the oxide superconductors the flux-pinning parameters are such that even a practical J/sub c/ definition is probably not useful.
Dissipation in high T/sub c/ thin films

   P. England, T. Venkatesan, T.L. Cheeks, H.G. Craighead, C.T. Rogers, S.-W. Chan, X.D. Wu and A. Inam

Summary: Current methods of fabricating Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7- delta / thin films by pulsed laser deposition result in films that are multicrystalline, with grain sizes of typically 1 mu m, or are quasi-monocrystalline, with no discernable grain boundaries, according to whether the deposition is carried out at high or low temperatures, respectively. The authors studied the electrical characteristics of both these types of material. It was found that the I-V characteristics of the granular material follow the rule V alpha (I-I/sub c/)/sup x(T)/ over at least six orders of magnitude in voltage, at all temperatures and magnetic fields. In addition, x(T) changes sharply from x=1 to x=2 at the temperature at which I/sub c/ becomes finite. This behavior can be explained quantitatively by a phase-ordering transition. The nongranular material has a much sharper resistive transition and larger critical current. The authors examined the variation of critical current with magnetic field and temperature in this material and observed an exponential suppression of J/sub c/ with magnetic field.
Effects of irradiation induced lattice disorder in superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ films

   P. Schmitt, H. Adrian, W. Gerhauser, G. Adrian and R. Stumpf

Summary: A report is presented on the preparation of thin films of the high-T/sub c/ superconductor YBa/sub 2/Cu/sub 3/O/sub 7/ by DC-magnetron sputtering and the effects of structural disorder introduced by irradiation with 25 MeV /sup 16/O-ions on superconductivity and normal state electrical resistivity. By suitable heat treatments polycrystalline films of different quality could be prepared on SrTiO/sub 3/ and Al/sub 2/O/sub 3/ substrates. The upper critical field B/sub c2/(T) of high-T/sub c/ films measured up to 6 T is linear with dB/sub c2//dT=-2 T/K. Irradiation with 25 Me oxygen ions leads to a linear reduction of T/sub c/ and an increase of rho (100 K) with fluence. The sensitivity of T/sub c/ to irradiation depends significantly on the quality of the films. For high-T/sub c/ films B/sub c2/(T) remains linear with increasing slope for defect-induced T/sub c/-depressions of about 30 K. As possible mechanisms for the observed T/sub c/-degradation, a defect-induced metal-to-semiconductor transition, which may be caused by a change of the local stoichiometry, and electron localization are discussed.
Microstructural characterization of YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films on SrTiO/sub 3/ using four-axis X-ray diffraction

   J. Sizemore, R. Barton, A. Marshall, J.C. Bravman, M. Naito and K. Char

Summary: Microstructural characteristics of YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films on SrTiO/sub 3/ have an important influence on their physical properties. Four-axis X-ray diffraction methods have been used to characterize textured and nontextured phases in several YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films deposited on single-crystal SrTiO/sub 3/. The type of epitaxial orientation of a- and c-axis textured films has been analyzed by tilting the specimen and observing the distribution of YBa/sub 2/Cu/sub 3/O/sub 7- delta / (102) plane X-ray intensities over 95% of the reciprocal lattice hemisphere. The ratio of a- to c-axis material was determined. Several films were found to contain nonepitaxially oriented YBa/sub 2/Cu/sub 3/O/sub 7- delta /, Y/sub 2/BaCuO/sub 5/, and BaCuO/sub 2/. Methods for quantifying the amounts of these random phases are discussed. The existence of stacking faults, such as those caused by the presence of extra Cu-O planes in YBa/sub 2/Cu/sub 3/O/sub 7- delta /, can sometimes manifest itself as a broadening and shifting of diffraction peaks. Consistent with the X-ray data, the stacking faults are readily seen in high-resolution electron microscopy images.
Spatial resolution limit for the investigation of high-T/sub c/ films by low temperature scanning electron microscopy

   R. Gross, M. Hartmann, K. Hipler, R.P. Huebener, F. Kober and D. Koelle

Summary: Low-temperature scanning electron microscopy represents a promising technique for studying the local superconducting properties of high-T/sub c/ films. The spatial and temporal structure of the electron-beam-induced thermal perturbation of high-T/sub c/ films and the resulting spatial resolution limit are discussed. Typical examples illustrating the imaging technique are presented.
Oxidation kinetics in oxygen deficient YBa/sub 2/Cu/sub 3/O/sub 7-x/ studied by neutron powder diffraction

   J. Als-Nielsen, N.H. Andersen, C. Broholm, K.N. Clausen, B. Lebech, M. Nielsen and H.F. Poulsen

Summary: A high-resolution, multidetector neutron powder diffractometer has been constructed and used for online studies of the oxidation kinetics in ceramic powders of oxygen-deficient YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBACUO). The structural phase transition between ordered orthorhombic and disordered tetragonal phase has been studied in pure oxygen and under vacuum. A continuous transition at 655 degrees C is observed in a pure oxygen atmosphere under equilibrium conditions, whereas an irreversible transition is observed at 470 degrees C under vacuum. Reduced YBACUO corresponding to x approximately=1.0 has been obtained by evacuation at 705 degrees C and has been shown to be stable in air. The oxidation processes of reduced YBACUO in a pure oxygen atmosphere have been studied using a semidynamical stepwise increase in temperature and under isothermal conditions. The results show that the in-diffusion under oxidation of reduced YBACUO is more easily accomplished than the corresponding out-diffusion process under reduction. From the structural data it is concluded that oxidation takes place in a mixed-phase medium of coexisting tetragonal and orthorhombic phases.
Superconductivity and crystal structure peculiarities of the oxygen deficient YBa/sub 2/Cu/sub 3/O/sub 7- delta / compounds

   V.G. Bar'yakhtar, I.G. Mikhailov, A.E. Morozovsky, V.V. Nemoshkalenko, V.M. Pan, S.K. Tolpygo, M.G. Vasilenko-Sheremetiev, V.S. Melnikov and N.P. Pshentsova

Summary: Crystal structure peculiarities, oxygen atom and vacancy ordering, and superconducting properties of YBa/sub 2/Cu/sub 3/O/sub 7- delta / compounds were investigated for the oxygen deficiency range O< delta <0.8. It was shown that the orthorhombic-to-tetragonal phase transition and oxygen-atom-ordering process are quite different phenomena and are observed at different temperature ranges. Oxygen disordering in the z=o plane is thermally activated and occurs mainly at low temperatures, when oxygen depletion by heating above 400 degrees C leads to the significant local reduction of the negative charge at the z=o plane. To restore a charge balance, lattice negative and positive ions have to be driven to shift along the z-axis in opposite directions. These structure changes cause an increase in the distances between layers. The superconducting transition temperature T/sub c/ appears to decrease along with delta . T/sub c/ versus delta dependence has a two-step-like shape, for which an explanation is offered.
Superconductivity, critical current density, and magnetic properties of Fe-substituted Y/sub 1/Ba/sub 2/(Cu/sub 1-x/Fe/sub x/)/sub 3/O/sub z/ materials

   S.T. Sekula, J. Brynestad, D.K. Christen, J.R. Thompson and Y.C. Kim

Summary: The superconductive properties of a series of Fe-substituted Y/sub 1/Ba/sub 2/(Cu/sub 1-x/Fe/sub x/)/sub 3/O/sub z/ materials, with x=0 to 10 at.%Fe, have been studied. It was found that the T/sub c/ decreased linearly with Fe content x at the rate of 6.7 K/at.%. The intragranular critical-current density J/sub c/ decreased exponentially both with reduced temperature, T/T/sub c/, and Fe concentration. Since the addition of Fe strongly drives the structure toward tetragonality, it is concluded that neither copper-oxygen chains nor macroscopic twinning is essential for high-temperature superconductivity.
Applicability of oxide superconductor to magnetic shielding

   T. Okada, K. Takahata, S. Nishijima, S. Yoshida and T. Hanasaka

Summary: Magnetic shielding capability has been investigated on the Y-B-Cu-O oxide superconductor, aiming at a practical use of oxide superconductors. Critical-transport-current density and magnetization were measured using the four-terminal and electromagnetic methods at temperatures of 77 K and 4.2 K. The results indicated that the critical-current density by the transport measurement was two orders of magnitude lower than that by the magnetization. This means that the larger shielding currents were found to be induced in the grain. The magnetic field behind the disk-shaped specimen was measured using a magnetic sensor. The shielding capability does not depend upon the critical-current density derived from magnetization but the critical-transport-current density. The applicability of oxide superconductors to magnetic shielding is discussed.
A superconductive shielding can for high T/sub c/ SQUID

   G.J. Cui, S.G. Wang, H.M. Jiang, J.Z. Li, C.Y. Li, C.D. Lin, R.Z. Liu, Q.L. Zheng, Y.S. Fu, Z.L. Luo and W.C. Qiao

Summary: The authors have fabricated yttrium-barium-copper-oxygen ceramic superconductive shielding cans and measured the magnetic shielding properties at liquid-nitrogen temperature by using a Hall magnetic sensor and high-T/sub c/ SQUID (superconducting quantum interference device). They report the fabrication processing of the shielding cans and the measurement results. The magnetic properties of the bulk samples are very different from those of conventional superconductors. There are lots of grain boundaries and defects inside the ceramic samples. The magnetic field can penetrate through those defects into the sample easily. The physical density of the samples is of great importance for their superconductive magnetic shielding ability. The isostatic pressing technique, which has been used in this work to prepare a dense and uniform cylinder, is a key processing method.
DC critical currents in superconducting ceramic samples of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/

   G. Paterno, C. Alvani, S. Casadio, U. Gambardella and L. Maritato

Summary: DC transport critical currents have been measured on Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ pellets, sintered under different conditions. Samples with a density ranging from 3.8 to 5.42 g/cm/sup 3/ have been investigated. The magnetic-field dependence of the critical current has been measured at liquid-nitrogen temperature. High-density samples, sintered at temperatures exceeding 950 degrees C, exhibit lower critical-current densities and a stronger dependence on a weak magnetic field.
Voltage-current characteristics of bulk YBa/sub 2/Cu/sub 3/O/sub 7-x/ superconductors

   Dingan Yu, Junping Tang and Dunhou Zhang

Summary: V-I characteristics of the sintered bulk YBa/sub 2/Cu/sub 3/O/sub 7-x/ superconducting samples with J/sub c/ ranging from 30 to 1000 A/cm/sup 2/ were measured in zero applied magnetic fields and at liquid-nitrogen temperatures by using a microcomputer-controlled I/sub c/ measuring system. The results show that the V-I characteristics of these oxide superconductors can be divided into four stages. In the first stage, where voltage starts to go upwards, the voltage can be expressed as an exponential function of the transport current, which is different from the power relation often seen in the cases of traditional superconductors such as NbTi alloys. In the second stage, the voltage is a linear function of the current, but its slope is much smaller than the normal-state resistance of the sample. Finally, an unstable stage characterized by a sharply rising voltage appears before the V-I characteristic is turned into a normal-state one. These features of the V-I characteristics are closely related to the inhomogeneity existing in the sintered oxide superconductors.
Superconductivity and crystal structure of high T/sub c/ Bi-Ca-Sr-Cu-O compounds

   V.M. Pan, V.P. Dovgopol, A.G. Popov, V.B. Spivakovskij, V.S. Flis, A.V. Zhalko-Titarenko, V.G. Bar'jakhtar, A.E. Pashitskij, V.S. Melnikov, N.P. Pshencova, D.P. Demenko and S.M. Rjabchenko

Summary: The superconducting properties, phase chemical composition and crystal structure of Bi-Ca-Sr-Cu-O system sintered samples were investigated. Twostep resistive superconducting transitions with a 120 K T/sub c/ onset were observed. The dominant phase composition might be formulated as Bi/sub 2/CaSr/sub 2/Cu/sub 2+x/O/sub y/ where x=0.4-1.0, depending upon the heat-treatment procedure.
Critical current characteristics in high T/sub c/ superconductors

   T. Matsushita and B. Ni

Summary: Critical-current densities of superconducting oxides are theoretically estimated for single-crystalline thin films and polycrystalline bulk materials with oriented and random textures. The percolation theory is used, and the effect of depression of the transport current through grain boundaries is taken into account. The results are compared in detail to previously published experimental results.
Estimation of stability and critical current density of oxide superconducting wires

   S. Nishijima, K. Takahata, T. Okada, Y. Sakai, K. Ikisawa, T. Mori, N. Takasu, K. Ikeda and K. Ueminami

Summary: The critical-current density of the high-T/sub c/ oxide superconductor, YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO), has been measured changing the temperature down to liquid-nitrogen temperature (LNT) in order to estimate the adiabatic and cryogenic stabilities at LNT. In estimating the critical-current density, both four-terminal and magnetization measurements were made. The specific heat was also measured. The adiabatic stability was found to be much higher than that of conventional superconductors at liquid-helium temperature. The cryogenic stability, however, is found to be poor.
Hall effect and Hall resistivity in REBa/sub 2/Cu/sub 3/O/sub 7- delta /

   N. Thier and K. Winzer

Summary: Results of Hall effect and Hall resistivity measurements for single-phase REBa/sub 2/Cu/sub 3/O/sub 7- delta / (RE=Y, Sm, Gd, Dy, Tm, Yb) and YBa/sub 2/Cu/sub 3/O/sub 7- delta / single crystals around and above T/sub c/ are reported. For all polycrystalline samples the Hall numbers V/sub 0//R/sub H/e are positive and show a linear temperature dependence in the range 120 K
Characterizing the current carrying capacity of different high T/sub c/ superconductors with as much sensitivity as versatility

   P. Metra, L. Gherardi and R. Mele

Summary: To qualify quickly new or optimized versions of high-T/sub c/ ceramic superconductors that are not available in the shape of a wire, two simple and accurate methods have been set up. The first measures the transport critical-current density of small sintered specimens or films with no electrical contacts, using a standard magnetic-core transformer with a washer of superconducting material fitted as a shorted, one-turn secondary winding. The current is induced in the specimen by exciting the primary coil with AC, and the resulting magnetic flux is very accurately measured with a pick-up coil and a lock-in amplifier. A similar approach, in which a small superconducting disk is introduced to replace an air gap in the magnetic circuit, measures the AC susceptibility components. This method can be used to study the effect of both temperature and magnetic field (up to 80 Oe) by clearly discriminating between intra- and inter-grain conduction transitions. Results of measurements on YBa/sub 2/Cu/sub 3/O/sub 7- delta / and bismuth compounds are presented.
Influence of fast neutron irradiation on inter- and intragrain properties of ceramic YBa/sub 2/Cu/sub 3/O/sub 7/

   H. Kupfer, U. Wiech, I. Apfelstedt, R. Flukiger, R. Meier-Hirmer, T. Wolf and H. Scheurer

Summary: Fast neutron irradiation of YBa/sub 2/Cu/sub 3/O/sub 7/ leads to a decrease of T/sub c/, the variation of the ratio T/sub c/( Phi t)/T/sub c/(O) being comparable to that observed in conventional superconducting compounds. Superconductivity vanishes above a fluence of 2*10/sup 19/ cm/sup 2/. The phase-locking temperature of the intergrain junctions decreases faster with fluence than T/sub c/. Lower AC losses due to a complete destruction of weak links and lower intergrain critical-current densities with increasing fluence reflect in addition a larger radiation sensitivity of the intergrain junction properties. The intragrain critical-current density j/sub cG/ increases with increasing fluence, but its dependence on B and Phi t is not at all in accordance with increasing pinning by radiation-induced defects and decreasing T/sub c/. The intragrain current drops remarkably at low fields, passing a minimum and a subsequent maximum beyond which the common decrease of j/sub cG/ with increasing field is observed. The low-field behavior, together with the much lower increase of j/sub cG/ with fluence than above the maximum, points to a junction character of the current in this field range.
Substitution of Mn for Cu in the high T/sub c/ superconductor YBa/sub 2/Cu/sub 3/O/sub 7- delta /

   R.F. Jardim, S. Gama, O.F. de Lima and I. Torriani

Summary: Samples of YBa/sub 2/(Cu/sub 1-x/Mn/sub x/)/sub 3/O/sub 7- delta /, with x=0.0, 0.025, 0.05, 0.075, 0.10, 0.15, and 0.20, were prepared by the solid diffusion method. Superconductivity with T/sub c/ in the range of 84-92 K was observed through electrical resistivity and magnetic susceptibility measurements. The substitution of Mn for Cu practically did not affect the onset temperature in the resistive transition, although a strong correlation between the transition width broadening and the increase of Mn content was observed. This fact is consistent with the reduction of the superconducting volume fraction determined through the normalized susceptibility data. X-ray diffraction revealed the occurrence of additional phases increasing with the Mn concentration.
High magnetic field studies of YBa/sub 2/Cu/sub 3/O/sub 7/ and NdBa/sub 2/Cu/sub 3/O/sub 7/ single crystals

   J.S. Moodera, J.E. Tkaczyk and P.M. Tedrow

Summary: The authors have measured the upper critical magnetic field H/sub c2/ of single crystals of the high-T/sub c/ superconductors YBa/sub 2/Cu/sub 3/O/sub 7/ and NdBa/sub 2/Cu/sub 3/O/sub 7/ as a function of crystal orientation in DC fields up to 31.5 T. The temperature dependence and anisotropy of H/sub c2/ and inferences concerning spin-orbit scattering are discussed. The lowest value of critical field is obtained for the crystal orientation which makes the applied field perpendicular to the Cu-O planes and is not much different from the values of H/sub c2/ for some conventional superconductors.
Weak link behavior in polycrystalline BaPb/sub 0.75/Bi/sub 0.25/O/sub 3/

   L. Cooley, M. Daeumling, T.C. Willis and D.C. Larbalestier

Summary: A study has been made of the critical-current densities of polycrystalline samples of the perovskite oxide superconductor BaPb/sub 0.75/Bi/sub 0.25/O/sub 3/ (BPB). BPB does not have the complications of twin boundaries and a highly anisotropic unit cell as is found in the high-T/sub c/ oxide superconductors (HTSC), and the coherence length ( xi ) is much longer than in HTSC materials ( approximately 7 nm as compared to approximately 0.5 to 2.5 nm). Thus some problems which have proved quite complex for HTSC materials (e.g. twin pinning or weak links) should be absent or have a different character in BPB. The authors have produced several samples of BPB. X-ray diffraction showed that the samples were single-phase, but an electron microprobe was used to identify about 1 vol.% of other phases present. The authors found that the transport critical-current density, as high as 2 A/cm/sup 2/ in zero field, drops markedly in fields of only 0.1 T. Flux penetration measurements place the magnetization critical-current density at about 10/sup 4/ A/cm/sup 2/. This large discrepancy is attributed to weak links.
Silver encased high temperature superconductor ribbons produced by rolling

   G.A. Whitlow, N.C. Iyer, A.T. Male, J.C. Powell and G.R. Wagner

Summary: Ribbons of silver/yttrium-barium-copper oxide/silver (Ag/YBCO/Ag), nominally 0.01 in. (0.25 mm) thick, have been fabricated by unidirectional rolling and their resulting microstructures and superconducting properties evaluated. The influence of a postfabrication sinter/oxygen replenishment anneal on their properties has been determined. Grain alignment/preferred orientation of the YBCO core was observed. Typical transport critical-current densities measured in zero field at 4.2 and 77 K were 600 and 125 A/cm/sup 2/, respectively. Preliminary experiments on the bismuth-containing high-temperature superconductors have indicated that codeformation of a silver composite billet by rolling to thin strip is easily accomplished.
Preliminary studies for the development of superconducting composite wires

   V. Provenzano, W.F. Henshaw, A.S. Edelstein, A.K. Singh, M.A. Imam, M.S. Osofsky, E.F. Skelton and S.B. Qadri

Summary: The results reported are part of a larger effort, the basic aim of which is to develop high-T/sub c/ superconducting composite wires, films, and thin-gauge panels with large current carrying capacity and engineered thermal and mechanical properties. The results relate to the following aspects of this ongoing research effort: the sputtering parameters used to deposit Bi-Sr-Ca-Cu-O films on MgO and other substrates; a dipping technique to produce Bi-Sr-Ca-Cu-O superconducting layers and wires; the postannealing heat treatments; the characterization of the microstructure and crystallographic features of the deposited films; and the superconducting properties of the films, layers, and wires.
Anisotropies in the magnetic penetration depth and critical current density of R/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ (R=Y or Ho), measured on magnetically-aligned powder composites

   D.K. Christen, Y.C. Kim, S.T. Sekula, J.R. Thompson, J. Brynestad, B.C. Sales, L.A. Boatner and J.D. Budai

Summary: Dispersed, uniaxially-aligned powder composites of R/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ (R=Y or Ho) were formed by suspending the powder in a liquid organic matrix that was then solidified in a magnetic field. From the observed particle dimensions and magnetic susceptibility measurements for fields applied either parallel or perpendicular to the Cu-O planes, the authors infer anisotropies in the superconducting magnetic penetration depth lambda . From the magnetization hysteresis in the mixed state they derive relative anisotropies in the critical-current densities J/sub c/. The observed anisotropies are qualitatively similar for both rare-earth-based materials but show some quantitative distinctions.
ARXPS, SEM, and SAM studies of highly textured YBa/sub 2/Cu/sub 3/O/sub x/ films

   J. Halbritter, B. Hauser, E.G. Keim, H.-J. Mathes, P. Walk and H. Rogalla

Summary: The electric conduction in the new cuprate superconductors suffers from intragrain and intergrain weak links. In transition metal oxides weak links show up in a specific chemistry, which can be measured by X-ray photoelectron spectroscopy and by Auger electron spectroscopy. To measure a defective local chemistry, the chemical signature of the reaction cinder has to be identified and the chemical signature of the perfect crystal has to be established. For highly textured cuprate films this has been done successfully, yielding the signature of the reaction cinder, e.g. BaO/sub 2/ or graphite, the signature of the interface reactions, e.g. Ba-aluminate on Al/sub 2/O/sub 3/ or Cu diffusion into MgO, and the signature of c-axis surfaces being a BaO/sub x/ layer on YBa/sub 2/Cu/sub 3/O/sub x/, which results in a 1-nm-thick insulating layer.
Properties of the new high T/sub c/ materials: an analysis based on fermiology

   V.Z. Kresin, G. Deutscher and S.A. Wolf

Summary: A small value of the Fermi energy, E/sub f/, in the new high T/sub c/ oxides and its consequences are the subject of this study. It is shown that the small value of E/sub f/ allows separation of the electronic contribution to the heat capacity in the high-temperature region E/sub f/k/sub B/>T> theta /sub D/ to determine the value of the electron-phonon coupling constant lambda . The linear temperature dependence of the normal resistance is mainly due to a large anisotropy of the system. A small value of E/sub f/ allows the lattice contribution to the thermal conductivity to play a dominant role. A strong electron-phonon coupling is manifested in the increase of the thermal conductivity in the region T
Measurement and correlation of optical and TEM twins in Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7- delta/

   L.S. Chumbley, J.D. Verhoeven, M.R. Kim, A.L. Cornelius and M.J. Kramer

Summary: The spacing of the twins present in Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7- delta / has been investigated using optical and transmission electron microscopy (TEM). Studies have reported that the value of the average twin spacing obtained by optical measurements is much larger than that measured in thin foils prepared for TEM observation, and controversy exists as to the exact nature of the optical twins. Experiments have been conducted which show that the twins observed optically correspond to those seen using TEM and are not produced by an optical interference effect. Using electron channeling, equations have been formulated which allow optical determination of the true spacing of twins present in a selected grain as well as the orientation of that grain. The average twin spacing measured by TEM has been found to vary with the sample preparation method, being smaller for crushed chip samples than for bulk samples prepared by ion milling or jet-polishing. A variation of the twin spacing with grain size has also been noted.
Transport and structural properties of Bi-Sr-Ca-Cu-oxide thin films prepared by reactive magnetron sputtering

   D.W. Face, J.T. Kucera, J. Crain, M.M. Matthiesen, D. Steel, G. Somer, J. Lewis, J.M. Graybeal, T.P. Orlando and D.A. Rudman

Summary: Highly oriented superconducting thin films of Bi-Sr-Ca-Cu-oxides have been reproducibly prepared by reactive magnetically-enhanced triode sputtering using three separate metal targets (Sr, Ca, and Cu-Bi). The as-deposited films had composition ratios of Bi:Sr:Ca:Cu that were very close to either 2:2:1:2 or 2:2:2:3. The films were deposited on SrTiO/sub 3/, MgO, CaF/sub 2/, Al/sub 2/O/sub 3/, and yttria stabilized zirconia (YSZ) substrates and had thicknesses of about 250 nm. After deposition, the films were annealed to 850-900 degrees C in various partial pressures of oxygen (0.05, 0.2 and 1 atm). Films deposited on
Critical current density measurements of thin films of YBaCuO

   L.H. Allen, J.H. Claasen and P.R. Broussard

Summary: Thin films of the YBaCuO superconductor have been deposited by evaporation on SrTiO/sub 3/ substrates. After a post-anneal, the films were patterned into a four-probe geometry, and critical-current density measurements were made using a transport technique. Compositions both on and off the stoichiometric Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ were studied, and measurements were made as a function of temperature and magnetic field. At 4.2 K and in ambient field, a stoichiometric film has a J/sub c/ greater than 10/sup 6/ A/cm/sup 2/ which falls off slowly out to approximately=55 K and then follows a power law dependence (1-t)/sup 3.3/, where t is the reduced temperature. The magnetic-field dependence of J/sub c/ at 4.2 K is weak, and for applied fields of 90 kOe, J/sub c/ has dropped only a factor of 10 from the ambient field. Off-stoichiometric films have lower J/sub c/'s which fall off faster and at lower temperatures.
Torque measurements of textured Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ sintered pellets

   F. Celani, L. Fruchter, C. Giovannella, R. Messi, S. Pace, A. Saggese and N. Sparvieri

Summary: The authors present at 4.2 K magnetic torque balance study of a textured sintered YBCO sample produced by pyrolysis using in the thermal treatments an ozone-enriched oxygen atmosphere. The shape of the torque signal as a function of the angle and of the measuring field shows features that are intermediate between those of a standard sintered pellet and those of a single crystal. The anisotropic experimental values of the lower critical field H/sub c1/ compare rather well to those previously found on YBCO single crystals. The intensity of the remaining magnetization, measured after a field cycling procedure, suggests the existence of a strong pinning for H>or=H/sub c1//sup (c)/ along the c-axis.
Thin film growth of oxide superconductor materials

   R.L. Henry, E.J. Cukauskas, S.B. Qadri, A.H. Singer and G.G. Campisi

Summary: Thin films of YBa/sub 2/Cu/sub 3/O/sub 7/, YBa/sub 2/Cu/sub 3/O/sub 7/:Ag and Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8/ have been grown by spray pyrolysis of aqueous nitrate solutions. Substrate temperatures in the range of 300 degrees C to 875 degrees C have been investigated. Following deposition, the films were annealed in flowing oxygen at 960 degrees C for YBa/sub 2/Cu/sub 3/O/sub 7/ and 850 degrees C for Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8/. The unit cell size of YBa/sub 2/Cu/sub 3/O/sub 7/:Ag did not change from that of YBa/sub 2/Cu/sub 3/O/sub 7/ but the X-ray diffraction patterns for the YBa/sub 2/Cu/sub 3/O/sub 7/:Ag films show that the
Characterization of thin YBaCuO films grown by coevaporation

   P.R. Broussard, J.H. Claassen and S.A. Wolf

Summary: Thin films of the Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub x/ superconductor have been grown by coevaporation and postannealing in oxygen on substrates of (100) SrTiO/sub 3/, (100) MgO, and (100) Yttria-stabilized Zirconia. Films grown on SrTiO/sub 3/ show evidence of both a- and c-axis growth normal to the substrate and strong in-plane order. Films on MgO show c-axis growth without any in-plane order, indicative of fiber texture. Transition temperatures of the films on MgO are depressed compared to those on SrTiO/sub 3/, but by using higher post-anneal temperatures we are able to improve the superconducting behavior of MgO samples.
Bi-Ca-Sr-Cu-O superconductors: the connectivity issue

   R. Ramesh, G. Thomas, S.M. Green, M.L. Rudee, Y. Mei and H.L. Luo

Summary: The connectivity problem in Bi-Ca-Sr-Cu-O superconductors is addressed. The bulk samples always exhibit a step in the resistivity plot, consequent to which zero resistance is obtained around 75 K, although the onset is above 110 K. Magnetic measurements indicate the presence of almost equal fractions of two superconducting phases with transition temperatures of 110 K and about 80 K. The microstructure of these samples has been examined using several transmission electron microscopy techniques. The superconducting phases exhibit a polytypoid-type structure with the general formula of Bi/sub 2/Sr/sub 2/Ca/sub n-1/Cu/sub n/O/sub y/, where n takes on values of 1,2,3, and, in some infrequent cases 4. The c-parameter and T/sub c/ increase with n. In almost all the superconducting grains, the lower T/sub c/ (n=1 or 2) polytypoid is observed at the grain boundaries. Thus, the 110 K polytypoid in each grain is not 'connected' to similar regions in other grains. The lower T/sub c/ polytypoid is observed at the grain boundaries due to a reduction of Ca and/or Cu. It is suggested that the controlled addition of PbO allows the formation of a Pb-rich liquid phase which makes the composition near the grain boundaries uniform. Consequently, the step in the resistivity plot disappears.
High temperature superconductors in the radiofrequency field

   J. Pirnat, J. Luznik and Z. Trontelj

Summary: The characterization of high T/sub c/ superconducting materials by a superregenerative radio frequency oscillator is considered. The physical principles of measurements performed on different YBa/sub 2/Cu/sub 3/O/sub 7- delta / samples are presented. A strong, reproducible and measurable effect on the superregenerative oscillator output was noticed when the sample in the tank circuit coil subjected to the low magnetic modulation field (about 4 mT, 25 Hz) passed through the superconductive transition in either direction. The signal is roughly independent of the spectrometer frequency from 2 MHz to 350 MHz. The results of measurements of the signal shape, the frequency shift, the line splitting and the influence of applied DC magnetic field are discussed.
VAMAS intercomparison of critical current measurement in Nb/sub 3/Sn wires

   K. Tachikawa, K. Itoh, H. Wada, D. Gould, H. Jones, C.R. Walters, L.F. Goodrich, J.W. Ekin and S.L. Bray

Summary: A technical working party in the area of superconducting and cryogenic structural materials has recently carried out the first worldwide intercomparison of critical-current, I/sub c/, measurement on multifilamentary Nb/sub 3/Sn wires. Three sample wires were supplied from each of the European Community countries, Japan, and the United States. There were few restrictions for the I/sub c/ measurement at participant labs. The standard deviations of the I/sub c/ values reported from these labs varied among test samples, and were 6-21% of averaged I/sub c/s at 12 T.
Nb/sub 3/Sn critical-current measurements using tubular fiberglass-epoxy mandrels

   L.F. Goodrich, S.L. Bray and T.C. Stauffer

Summary: A systematic study of the effect of sample mounting techniques on the superconducting critical-current measurement was made. A seemingly small change in mandrel geometry can result in a 40% change in the measured critical current of a Nb/sub 3/Sn sample at 12 T. This is a result of a change in the conductor prestrain at 4 K caused by variation in thermal contraction between thick-and thin-walled fiberglass-epoxy composite (G-10) tubes. An approximate measure of the vibrations in thermal contraction (from room to liquid-nitrogen temperature) indicate a 0.2% greater contraction for the thick-walled tube. This difference, combined with strain sensitivity measurements, is consistent with the observed decrease in critical current.
Effect of transverse compressive stress on the critical current of cabled Nb/sub 3/Sn conductor

   B. Jakob and G. Pasztor

Summary: A test apparatus has been designed and built for the investigation of cabled conductors subjected to transverse load. The apparatus permits measurement of compressive stress on a loaded multistage flat cable when a transport current is applied to one of its constituent subcables. With the apparatus, the critical-current behavior of a solder-filled Nb/sub 3/Sn cable made by the external diffusion method exposed to transverse loads up to 165 MPa, was investigated. A field-dependent degradation of the critical current was found. The effect is completely reversible up to about 100 MPa. Solder-filled cables as used in large-current applications are less sensitive to transverse compressive stress than single wires. A 150 MPa compressive load on the SULTAN cable, for example, degrades the critical current by 31% at 11 T. This is still a high enough value in view of the large transverse compressive stress acting on conductors required for fusion magnets.
The critical density throughout the superconducting phase of multifilamentary Nb/sub 3/Sn wire for forced flow fusion applications measured using the Bean-Campbell AC magnetization technique

   D.P. Hampshire and D.C. Larbalestier

Summary: AC magnetization measurements for transverse orientation have been completed on a multifilamentary Nb/sub 3/Sn composite wire, which is a candidate for fusion applications. Using these data, it was possible to determine the critical-current density using the Bean-Campbell analysis in the ranges B
Measurements of the stability margin of a Nb/sub 3/Sn cable-in-conduit conductor

   T. Ando, M. Nishi and S. Shimamoto

Summary: The stability margin of a single quadruplex of Nb/sub 3/Sn/Cu composite strand enclosed in a round stainless-steel tube was measured by using an inductive heater whose duration time is around 0.1 ms. The strand had a diameter of 1.04 mm and a copper fraction of 69%. The fraction of helium in the cable space was 34.5%. Measurements of the stability margin were carried out by varying the transport current, external magnetic field, and initial helium pressure. The helium flow rate was always zero. The limiting transport current, which is the boundary value between the upper and lower stable regions similar to NbTi cable-in-conduit conductors, was observed. The limiting-current density over the cable space inside the conduit at 12 T was 100 A/mm/sup 2/, corresponding to 58% of the critical current. This value does not depend on the initial helium pressure in the range of 3-12 atm. Observed upper and the lower stability margins were more than 200 mJ/cm/sup 3/ strand and less than 60 mJ/cm/sup 3/ strand, respectively. The heat transfer coefficient in the cable-in-conduit conductor is estimated to be around 0.1 W/cm/sup 2/K.
Microwave studies of granular superconductivity

   A.M. Portis and K.W. Blazey

Summary: Microwave absorption in low magnetic fields is a sensitive contactless indicator of surface granular superconductivity, a significant source of surface resistance. Granularity is also responsible for microwave absorption in the ceramic high-temperature superconductors and in ceramic Chevrel-phase compounds. Modulated microwave adsorption signals from granular ceramics show critical behavior with pinning and depinning of intergranular flux over a modulation cycle. In single crystal YBa/sub 2/Cu/sub 3/O/sub 7- delta / the adsorption arises from the motion of flux within twin-plane domain boundaries. Modulated adsorption signals from these domain boundaries show additional adsorption from fluxon nucleation above critical levels of microwave current. Such losses may contribute significantly to microwave adsorption in zero magnetic field.
Microwave measurements on high T/sub c/ superconducting single crystals and films

   W.W. Fuller, F.J. Rachford, W.L. Lechter, P.R. Broussard, L.H. Allen and J.H. Claassen

Summary: The authors have studied the microwave properties of a single crystal of ErBa/sub 2/Cu/sub 3/O/sub 7-x/. The crystal was placed in the bottom of a rectangular TE 103 copper cavity whose resonant frequency was 9.2 GHz. The Q of the system, cavity and sample, as well as the frequency shift, was monitored as the system was cooled. Below about 50 K the measurements became limited by the copper cavity. Close to the superconducting transition, about 90 K, the real surface impedance is at least one order of magnitude higher than that calculated from Mattis and Bardeen's (1958) formula. The authors have also studied using both resonant and nonresonant methods the microwave properties of an oriented film of YBa/sub 2/Cu/sub 3/O/sub 7-x/ grown on a MgO substrate. For both types of measurements they have studied the effects of small magnetic fields, less than 100 G, on the microwave losses at 9.2 and 10 GHz in a microwave cavity and by a nonresonant technique. The results are discussed in terms of flux entry and pinning at grain boundaries.
Fabrication and microwave properties of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O thin films

   R. Sobolewski, J. Konopka, W. Kula, P. Gierlowski, A. Konopka and S.J. Lewandowski

Summary: Studies are reported of the interaction of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O thin films with microwaves. The films were prepared on cubic zirconia and magnesium oxide substrates using a modified spray deposition technique. The tested films were about 1-3 mu m thick and exhibited good superconducting properties. Several test structures have been designed by spraying a mixture of nitrate precursors on heated substrates through very thin stencil marks. The supercurrent dependence on millimeter wavelength microwave illumination was measured, and microwave detection and mixing experiments were performed. The films of both materials exhibited properties characteristic of granular superconductors, with Josephson-type coupling at the intergrain connections. The results also indicate that these materials can be successfully used as very sensitive millimeter radiation detectors operational at liquid-nitrogen temperatures.
Surface impedance measurements on high T/sub c/ superconductors

   G. Muller, D.J. Brauer, R. Eujen, M. Hein, N. Klein, H. Piel, L. Ponto, U. Klein and M. Peiniger

Summary: An investigation has been made of the RF properties of two oxide superconductors, mainly Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ and tentatively Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub x/, between 4.2 and 300 K at S-, K-, and W-band frequencies. The surface resistance R/sub s/ and the magnetic-field penetration depth lambda of ceramic pellets and of polycrystalline layers on silver substrates were measured in normal or superconducting host cavities. Improvement factors for R/sub s/ of up to three orders of magnitude at 3 GHz and one at 86 GHz have been achieved, but the temperature dependence of R/sub s/ deviates strongly from that of conventional superconductors. The main features are a slow fall-off near T/sub c/ and a remaining temperature dependence at 4.2 K, both depending on the preparation and the resulting homogeneity of the samples. From the frequency shift of the cavity near T/sub c/ the authors extrapolate lambda (0) values between 200 and 1300 nm. Large fractions of the samples remain superconducting up to surface current densities on the order of 10/sup 5/ A/cm/sup 2/.
RF properties of high-T/sub c/ superconductors

   C.L. Bohn, J.R. Delayen, D.I. Dos Santos, M.T. Lanagan and K.W. Shepard

Summary: An investigation was conducted of the RF properties of high-T/sub c/ superconductors over a wide range of temperatures, frequencies and RF field amplitudes. Both bulk polycrystalline samples and thick films on silver substrates were tested. At 150 MHz and 4.2 K, surface resistances of 18 mu Omega at low RF field and 3.6 m Omega at an RF field of 270 G were measured. All samples showed a strong dependence of the surface resistance on RF field. However, no breakdown of the superconducting state was observed up to the highest field achieved (320 G).
Relaxation behavior of ultrasonic attenuation in YBa/sub 2/Cu/sub 3/O/sub 7/

   K.J. Sun, W.P. Winfree, M.F. Xu, B.K. Sarma, M. Levy, R. Caton and R. Selim

Summary: It is shown that temperature-dependence ultrasonic attenuation data of YBa/sub 2/Cu/sub 3/O/sub 7/ at various frequencies exhibit anomalies at temperatures close to T/sub c/. These attenuation maxima are found to be the result of a relaxation mechanism added on top of an unusual attenuation background. It is proposed that the grain boundary motions induced by the structural distortion and the propagation of sound waves enhances the energy dissipation around T/sub c/. Whether this structural distortion is the consequence of the onset of a superconducting state remains undetermined. It is also possible that either a tunneling effect of the acoustoelectric effect contributes to sound energy dissipation. The temperature dependence of ultrasonic velocity shows a softening around T/sub c/ which may be an intrinsic property of high-temperature superconductors.
Ultrasonic measurements in sinter-forged high T/sub c/ superconductor YBa/sub 2/Cu/sub 3/O/sub 7- delta/

   M.F. Xu, A. Schenstrom, Y. Hong, D. Bein, B.K. Sarma, M. Levy, Z. Zhao, S. Adenwalla, A. Moreau, Q. Robinson, D.L. Johnson, S.J. Hwu, K.R. Poeppelmeier and J.B. Ketterson

Summary: Both ultrasonic attenuation and velocity as a function of temperature from 4.2 K to room temperature were measured on sinter-forged samples of YBa/sub 2/Cu/sub 3/O/sub 7- delta /, which have more than 80% alignment of the c-axis of the grains parallel to the forging axis. Strong anisotropy was found both in the attenuation and the velocity when propagating sound waves in different directions relative to the forging axis. Hysteresis was observed in the velocity changes.
In situ growth of superconducting YBaCuO using reactive electron-beam coevaporation

   N. Missert, R. Hammond, J.E. Mooij, V. Matijasevic, P. Rosenthal, T.H. Geballe, A. Kapitulnik, M.R. Beasley, S.S. Laderman, C. Lu, E. Garwin and R. Barton

Summary: Conditions required for in situ growth of YBaCuO thin films by reactive electron-beam evaporation have been explored. Three sources of activated oxygen (atomic oxygen from microwave discharge, plasma generated by electron beams, and an ion beam) were compared. The best results so far were obtained with atomic oxygen. Epitaxial films with high critical currents were grown on SrTiO/sub 3/ [100] and [110], Al/sub 2/O/sub 3/ (1102), and MgO [100] at 600 degrees C. Evaporation rates were controlled with a rate monitor using atomic absorption.
Growth and properties of sputtered high-T/sub c/ oxide thin films

   K. Char, M.R. Hahn, T.L. Hylton, M.R. Beasley, T.H. Geballe and A. Kapitulnik

Summary: Superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ films of thicknesses ranging from 500 AA to 5 mu m have been successfully made by the reactive magnetron sputtering technique. The effects of composition, annealing condition, and thickness of an epitaxial film on its orientation are discussed. films show anisotropic resistivities and critical-current densities that are orientation-dependent.
Fabrication and properties of Bi-Sr-Ca-Cu-O thin films made using pulsed laser deposition

   D.K. Fork, T.H. Geballe, J.B. Boyce, F.A. Ponce and R.I. Johnson

Summary: Superconducting films of Bi-Sr-Ca-Cu-O on (100) MgO were fabricated using the pulsed laser deposition technique to deposit from sintered and fluoride-containing disks. Fluoride-containing films were observed to anneal more rapidly and at slightly reduced temperatures and to contain an additional phase with 24.5 AA c-axis spacing. The preferred orientation of all films is c-axis normal to the substrate. On (100) SrTiO/sub 3/, heteroepitaxial growth of the Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub 8+ delta / phase was demonstrated using transmission electron microscopy.
Superconducting thin films of BiSrCaCuO made by sequential electron beam evaporation

   J. Steinbeck, A.C. Anderson, B.Y. Tsaur and A.J. Strauss

Summary: Superconducting thin films of Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ have been made by sequential electron-beam evaporation of multiple layers of Bi and Cu metals and (Sr,Ca)F/sub 2/ on MgO substrates. The films were annealed at high temperature, first in wet O/sub 2/ and then in dry O/sub 2/, and cooled to room temperature in dry O/sub 2/. The resulting films, which are approximately 1 mu m thick, have transition temperatures of approximately 85 K. X-ray diffraction shows that the films are preferentially oriented with their c-axis perpendicular to the MgO substrate. The best film has a zero-resistance temperature of 90 K and critical-current densities of 8*10/sup 4/ A/cm/sup 2/ at 77 K and 2.5*10/sup 5/ A/cm/sup 2/ at 4.2 K.
Improvement of average film quality in RBa/sub 2/Cu/sub 3/O/sub 7-x/ sputtered films

   R.W. Simon, C.E. Platt, K.P. Daly, A.E. Lee and M.K. Wagner

Summary: Thin films of RBa/sub 2/Cu/sub 3/O/sub 7-x/ (R includes Y, Er, and Nd) have been deposited by four-gun DC magnetron sputtering from metallic targets in a Xe-O/sub 2/ gas mixture and postannealed in flowing O/sub 2/. Extensive optimization of the film deposition process has been achieved for erbium-based films which can be produced with good characteristics on a variety of substrates. Fine-grained polycrystalline films with sharp resistive transitions are produced on single-crystal and polycrystalline YSZ, MgO, ZrO/sub 2/-buffered sapphire, and silver-buffered sapphire. Broader transitions are observed on buffered silicon wafers. These erbium films often show grain sizes as small as 20-30 nm and, with the addition of an RF oxygen glow discharge in the deposition system, are quite smooth despite furnace postannealing. Highly-oriented 1-2-3 film growth is observed on SrTiO/sub 3/ and LaAlO/sub 3/ single-crystal substrates. Four-point resistivity measurements show transitions as narrow as 1 K, while magnetization and RF frequency-shift measurements show more detail about film quality. Films are characterized by XRD, SNMS, Auger, XPS, and cross-sectional EDX profiling. The authors also report on the use of in-situ deposition of silver as a passivation layer for the 1-2-3 surface.
High temperature superconducting films by RF magnetron sputtering

   A.M. Kadin, P.H. Ballentine, J. Argana and R.C. Rath

Summary: The authors have produced sputtered films of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O by RF magnetron sputtering from an oxide target consisting of loose reacted powder. The use of a large 8-in stoichiometric target in the magnetron mode permits films located above the central region to be free of negative-ion resputtering effects, and hence yields reproducible, uniform stoichiometric compositions for a wide range of substrate temperatures. Superconducting YBCO films have been obtained either by sputtering at low temperatures followed by an 850 degrees C oxygen anneal, or alternatively by depositing onto substrates heated to approximately=600-650 degrees C and cooling in oxygen. Films prepared by the former method on cubic zirconia substrates consist of randomly oriented crystallites with zero resistance above 83 K. Those deposited on zirconia at medium temperatures without the high-temperature anneal contain smooth partially oriented crystallites, with a slightly depressed T/sub c/ approximately=75 K. Finally, superconducting films have been deposited on MgO using a BiSrCaCu/sub 2/O/sub x/ powder target.
Laser deposition of quality high T/sub c/ superconductor films

   C.C. Chang, T. Venkatesan, X.D. Wu, A. Inam, E.W. Chase, D.M. Hwang, J.M. Tarascon, P. Barboux, P. England and B.J. Wilkens

Summary: The laser deposition technique has been developed into a versatile method for depositing films of YBa/sub 2/Cu/sub 3/O/sub x/ material. A brief description is given of the method and important materials characteristics, such as composition, surface smoothness, crystalline structure, and interactions with substrates. T/sub c/ over 93 K, J/sub c/ in the 10/sup 6/ A/cm/sup 2/ range at 77 K, tolerance to high magnetic fields, low temperature deposition (near 650 degrees C), as-deposited superconducting films, epitaxial growth, and very smooth surfaces have been demonstrated. Relevance to practical application is briefly discussed.
Epitaxial feature of Y-Ba-Cu-O thin films prepared by multilayer deposition

   S.Z. Wang, Z.L. Bao, S.L. Wang, G. Li, Z.Y. Ye, C.Y. Li and D.L. Yin

Summary: Y-Ba-Cu-O thin films have been prepared on (100) SrTiO/sub 3/ substrates by a multilayer deposition technique using a single electron beam source. The epitaxial growth with a-axis normal to the film plane was confirmed by X-ray diffraction. The oriented growth phenomenon of the Y-Ba-Cu-O thin films is explained by theories of epitaxy and texture.
Investigation of the multilayer deposited BiSrCaCuO thin films

   B.B. Jie, S.L. Wang, Z.L. Bao, F.R. Wang, C.Y. Li, G. Li, S.Z. Wang and D.L. Yin

Summary: Superconducting BiSrCaCuO thin films with zero resistivity at 80 K have been prepared by a multilayer deposition and diffusion method. The nominal composition is BiSrCaCu/sub 2/O/sub y/. X-ray diffraction shows that the same lattice structure as for the bulk material but with strong preferred orientation in the film. The superconductivity of this kind of film is sensitive to treatment temperature but not sensitive to annealing atmosphere. Critical parameters have been measured and compared with the similar YBaCuO thin films.
Superconducting characteristics of YBCO films

   M. Muroi, T. Matsui, Y. Koinuma, K. Tsuda, M. Nagano and K. Mukae

Summary: An investigation has been made of superconducting YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) thin films, which were prepared with two synthetic processes using RF-magnetron sputtering: (a) deposition at low substrate temperature with postannealing at around 900 degrees C, and (b) deposition at high substrate temperature around 650 degrees C with or without postannealing. High-T/sub c/ superconducting YBCO thin films were obtained with either process. The films prepared with process (a) had, however, poor J/sub c/ below 10 A/cm/sup 2/ at 77 K and their surfaces were rough. The films prepared with process (b) had higher J/sub c/ and smoother surfaces. Further improvement in surface morphology was made by raising substrate temperature to 700 degrees C at the start of the deposition.
Chemi-physical diagnosis of BiSrCaCuO thin film preparation

   T. Kobayashi, Y. Fukumoto, H. Hidaka and M. Tonouchi

Summary: Thin film and bulk formation of the new high T/sub c/ superconductive oxide BiSrCaCuO (BSCCO) and related crystal structures has been investigated, emphasizing the beneficial effect of Mg addition on the superconductivity. The onset temperature of the high T/sub c/ phase was raised by a few degrees, and a T/sub c/ (zero) higher than 100 K was easy to obtain in the BiSrCaMgCuO system. The as-grown BSCCO thin film formation is also considered. Sputter-deposited to 48 K without using postanneal. After the film was subjected to the furnace anneal, T/sub c/ (zero) rose to 90 K, though most of the resistance dropped at even higher temperatures. The structural change and chemical shift introduced during the postanneal have been closely examined, showing that sensitivity of the BSCCO crystallinity to the substrate material, annealing time, and temperatures. These characteristic features seem substantially different from those of YBCO system.
Y-Ba-Cu-O thin films by evaporating the three elements using resistive heating

   A. Nakayama, N. Ochi, K. Takeuchi, H. Ito and Y. Okabe

Summary: High T/sub c/ superconducting Y-Ba-Cu-O thin films were fabricated by evaporating the three metal elements Y, Ba, and Cu using resistive heating. Subsequently, the films were annealed in oxygen in order to obtain the superconducting phase. The critical temperatures T/sub c/ (onset) and T/sub c/ (end) of the obtained film were 88 K and 65 K, respectively.
Fabrication and interface reaction of Y-Ba-Cu-O superconducting thin films by reactive ion beam coating

   C.X. Ren, G.L. Chen, Y. Zheng, J.M. Chen, J. Yang, C.S. Zhang, L.M. Xie and S.C. Zou

Summary: Y-Ba-Cu-O superconducting thin films have been fabricated by the reactive ion beam coating technique with good reproducibility. The influence of atom stoichiometry on the critical temperatures of the films is determined. Ba and Cu atoms diffusing into substrates were detected by auger electron spectroscopy and Rutherford backscattering. A thin silver film deposited on ZrO/sub 2/ substrate as a buffer layer can effectively retard the interface reaction.
High T/sub c/ superconducting thin films prepared by flash evaporation

   T. Hato, Y. Takai and H. Hayakawa

Summary: Superconducting thin films of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O were prepared by the flash evaporation technique. The flash evaporation method evaporates multi-elements instantly with different evaporation temperatures. These films had critical temperatures T/sub c/ (zero resistance) of 78 K (unannealed Y-Ba-Cu-O) and 73 K (annealed Bi-Ca-Sr-Cu-O). The thicknesses of these films were from 200 to 600 nm.
High T/sub c/ BiSrCaCuO superconductor grown by CVD technique

   M. Ihara, T. Kimura, H. Yamawaki and K. Ikeda

Summary: Single-crystal high-T/sub c/ BiSrCaCuO films were grown on (100) MgO substrates in an open-tube chemical-vapor deposition (CVD) system using metal-halide sources and oxygen gas. The morphology of the BiSrCaCuO superconducting layers and MgO insulating layers was satisfactory. The resistivities of the high-T/sub c/ layers at 300 K and critical temperatures were rho =5-20 m Omega -cm and T/sub c/=70-80 K for Bi/sub 1/Sr/sub 0.8/Ca/sub 1/Cu/sub 3.7/O/sub x/ layers 0.1-to-0.3- mu m thick on MgO substrates. The CVD system and characteristics of the high-T/sub c/ layers and MgO heteroepitaxial layers as a substrate are discussed.
Preparation of superconducting Bi-Ca-Sr-Cu-O thin films by RF magnetron sputtering

   Y. Yang, G.H. Dieckmann and J.E. Nordman

Summary: Superconducting thin films of Bi-Ca-Sr-Cu oxide, with T/sub c/ onset of approximately 90 K were prepared by RF magnetron sputtering on sapphire with and without a CaZrO/sub 3/ buffer layer, on ZrO-coated silicon (111), and on single-crystal MgO (100). The as-deposited films were amorphous insulators which were then annealed in various ways. Zero resistance at 72 K for films on (100) MgO was achieved after annealing in air at 810 degrees C for 2 h. However, the X-ray diffraction pattern showed that two superconducting phases, i.e., Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8+x/ (2122) and Bi/sub 2/Ca/sub x/Sr/sub 2-x/CuO/sub 6+y/ (2021), are present, and that films have preferred orientation with c-axis normal to the substrates.
Resistivity behavior during anneal of YBa/sub 2/Cu/sub 3/P/sub 7-x/ films

   A. Hohler, H. Neeb and C. Heiden

Summary: The resistivity behavior of sputtered YBCO films has been investigated during anneal at temperatures up to 1175 K. Characteristic variations in resistivity under different experimental conditions are related to microstructural changes and corresponding superconducting properties.
A simple method for preparing superconducting high T/sub c/ thin films

   P. Romano, A. Nigro, R. Vaglio, E. Signorelli and K.E. Gray

Summary: High-quality superconducting films of the high-T/sub c/ compound YBa/sub 2/Cu/sub 3/O/sub 7/ were prepared on sapphire using a simple method that combines DC magnetron sputtering from a single target and evaporation from a heated source. The method should be especially suitable for depositing thin films on complex surfaces. YBa/sub 2/Cu/sub 3/O/sub 7- delta / films with T/sub c/=92 K (onset) were prepared using a YCU/sub 3/ target and evaporating barium by a specially designed, feedback-controlled, molybdenum heater using either pure barium or barium-aluminum alloy. The films were characterized by X-rays, electron-dispersion spectroscopy, and other techniques.
YBCO superconducting thin films prepared by vacuum coevaporation without post treatment in oxygen

   S. Chromik, V. Strbik, S. Benacka, J. Levarsky, J. Sith, A. Plecenik, S. Gazi, V. Smatko and J. Schilder

Summary: Results on low-temperature preparation of superconducting thin films of YBa/sub 2/Cu/sub 3/O/sub x/ are presented. YBCO thin films of 0.5-1.0- mu m thickness were prepared by vacuum codeposition of Y, BaO, and Cu onto both polycrystalline and single-crystal Al/sub 2/O/sub 3/, MgO, and SrTiO/sub 3/ and on Si+SrTiO/sub 3/ and Si+SiO/sub 2/ substrates. The temperature of the substrates was 550-580 degrees C and the partial oxygen pressure in the vacuum chamber was 10/sup -2/ Pa. The preparation of in situ superconducting thin films was successful with all substrates. Maximum critical temperature at zero resistance was T/sub ce/=85 K, the onset critical temperature T/sub con/ being from 90 to 95 K. The authors believe that T/sub con/ represents the maximal critical temperature of grains. Thus, the synthesis of superconducting granules with high T/sub c/ is possible even at a relatively low temperature during the deposition. On the other hand, the zero-resistance critical temperature T/sub ce/ characterizes the intercrystalline boundaries with electrical properties sensitive to diffusion processes from substrate or surrounding atmosphere. Additional oxidation of films (thermal or plasmatic) does not much affect T/sub ce/ near 85 K.
Boundary layers of oxide superconductors films pasted on Al/sub 2/O/sub 3/, MgO, SrTiO/sub 3/ and YSZ

   K. Agatsuma, T. Ohara, K. Kaiho and H. Tateishi

Summary: Energy-dispersive X-ray analysis, wavelength-dispersive X-ray analysis, and scanning microscopy examinations have been performed for annealed Y-Ba-Cu-O(YBCO) and Bi-Sr-Ca-Cu-O(BSCCO) films which will be adopted for future superconducting devices. Relatively thin films pasted on various substrates and cross sections were tested. The influence of the annealing on the substrate and superconducting films has been investigated. The results show the formation of boundary layers of intermediate products, which consists of Ba compounds between the YBCO layer and substrate (Al/sub 2/O/sub 3/, SrTiO/sub 3/, and ZrO/sub 2/) and Sr and Bi compounds between the BSCCO layer and substrate (SrTiO/sub 3/, MgO, and ZrO/sub 2/).
Possibility of critical field enhancement due to field penetration in high-T/sub c/ sponges and thin films

   E.W. Collings, A.J. Markworth and K.R. Marken Jr.

Summary: Magnetic susceptibility measurements of a sample of sintered high-T/sub c/ ceramic superconductor of nominal composition Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-y/ were conducted as a function of temperature from liquid-He temperatures to T/sub c/. The fitted form of the susceptibility temperature dependence yielded a sample-particle size that was only a few times larger than the field-penetration depth. The particle size was much less than the grain size and commensurate with the thickness of the optical twins. The results of the enhancement studies are also discussed in the light of C.P. Bean's (1964) early experiments on Pb sponges (in this case lambda >> particle size) which exhibited spectacular enhancements of H/sub c/ in association with flux trapping at or between the Pb filaments. It is predicted that it should be possible, using presently available film-deposition techniques, to produce high-T/sub c/ films possessing severalfold enhancements of H/sub c1/ beyond the bulk value, and that, as with the Pb sponges, the magnetization loops, even when taken within what passes for the Meissner state in such materials, will be hysteretic.
Magnetic shielding effect on oxide superconducting plates

   A. Yahara and H. Matsuba

Summary: The authors have measured a critical shielding flux density B/sub 01/ of YBa/sub 2/Cu/sub 3/O/sub y/ superconducting plates. Sintered specimens were assumed to be bulk superconductors with interconnected sub-structures and were considered to screen the magnetic field completely for applied fields of less than B/sub 01/. The critical shielding flux density was proportional to the thickness d of the specimen, as expected from an equation derived from the Bean-London critical state model. The authors have obtained 16 G/mm as a maximum shielding capacity of B/sub 01//d. The measured flux showed hysteresis when the applied field was raised above B/sub 01//.
Magnetic shielding by superconducting Y-Ba-Cu-O hollow cylinders

   J.O. Willis, M.E. McHenry, M.P. Maley and H. Sheinberg

Summary: The authors have measured the magnetic field H' at the center of a hollow of sintered Y-Ba-Cu-O superconductor as a function of applied field H, temperature, tube length, and tube wall thickness. The maximum field that can be shielded H/sub sh/ agrees with the value calculated from the critical state model using the measured critical-current density J/sub c/. The maximum trapped field H/sub tr/ in the tube, on decreasing H to zero, exceeds H/sub sh/ by as much as a factor of two, and large enhancements in J/sub c/ are observed in the decreasing field. These phenomena are identified with intragranular flux pinning present only after H has exceeded H/sub c1/ of the grains. Finite tube length does not affect the H/sub tr//H/sub sh/ ratio appreciably. H/sub sh/ depends approximately on the square root of the wall thickness.
The fabrication and characterization of high temperature superconducting magnetic shields

   J.W. Purpura and T.R. Clem

Summary: Tubes fabricated of polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-x/ are characterized, and details of the fabrication procedure are discussed. The microstructure of the tubes determined by scanning electron microscopy and X-ray diffractometry is described. Resistive measurements of T/sub c/ and Delta T/sub c/ have been made. The tubes have also been characterized by means of SQUID (superconducting quantum interference device) magnetometry. The temperature dependence of magnetic fields trapped axially in the tubes has been measured and estimates of penetration depth are given. Moreover, measurements of the transverse shielding effectiveness of the tubes have been made and are compared with theoretical predictions. Studies on flux penetration into the tubes are described. Findings from the microstructure studies are correlated with the observed superconductivity properties. The results on the high-temperature materials are compared to results obtained previously on tubes made from conventional superconductors.
Meissner motor using high-T/sub c/ ceramic superconductors

   A. Takeoka, A. Ishikawa, M. Suzuki, K. Niki and Y. Kuwano

Summary: The authors developed a superconducting motor using high-T/sub c/ ceramic superconductors. This motor, which utilizes the repulsive force caused by the Meissner effect that appears below T/sub c/, is called the Meissner motor. The motor rotated at a maximum speed of 40 rpm. Though the repulsive force to drive the motor increased with the decrease of temperature or the increase of the gradient magnetic field, it was only about 1.1 gf/g at 77 K in 3500 G/cm. The motor has a maximum torque of 5.0 gf-cm theoretically, but actually had a torque below 0.66 gf-cm, because it took some time to be cooled below T/sub c/. The rotating speed of the motor was limited by heating ability, and its torque was limited by cooling ability.
Synchronous rotation of a floating magnet and flux penetration in Y-Ba-Cu-O superconductor

   J.C. Macfarlane, K.-H. Muller and R. Driver

Summary: An experimental demonstration of induced rotation of a rectangular magnet floating above a superconducting ring is described. Synchronism between the rotating and the applied alternating magnetic field was observed under certain conditions. The stability of the levitated magnet and the mechanism of the rotation are discussed on the basis of the authors' studies of flux penetration into superconductors.
Fabrication of Y-Ba-Cu-O superconductor for magnetic bearing

   M. Itoh, H. Ishigaki and A. Hida

Summary: Although high-T/sub c/ oxide superconductors, such as Y-Ba-Cu-O, should have great potential for application to repulsive magnetic bearings, various kinds of improvements on the mechanical and electrical properties of the materials are needed. The authors tried to improve these properties by changing compression pressure in the process used in forming a pellet systematically and by adding Ag powder to Y-Ba-Cu-O powder. All materials used here were confirmed as Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ by X-ray diffraction analysis. It was found that density, hardness, temperature of zero resistance, and ratio of resistivity at a temperature of 300 K and that at a temperature of 100 K increase as the compression pressure becomes higher. On the other hand, a temperature of resistance drop and a repulsive force due to the Meissner effect were insensitive to the pressure. The Ag content in the pellets makes the temperature of zero resistance higher. It was also found that the ratio of resistivity had possible use as a criterion for better superconductive characteristics.
Ozone processing of MBE grown of YBa/sub 2/Cu/sub 3/O/sub 7-x/ films

   D.D. Berkley, B.R. Johnson, N. Anand, K.M. Beauchamp, L.E. Conroy, A.M. Goldman, J. Maps, K. Mauersberger, M.L. Mecartney, J. Morton, M. Tuominen and Y.-J. Zhang

Summary: Results of a new process for producing high-quality thin films of the YBa/sub 2/Cu/sub 3/O/sub 7-x/ superconducting oxide are presented. This process uses a reactive ozone vapor at a molar rate commensurate with evaporated metal rates under true UHV conditions. A film exhibiting a superconducting onset at 87 K and zero resistance at 82 K was obtained. It was c-axis oriented and contained no second phases as determined by X-ray diffraction. The failure to produce good films by depositing BaF/sub 2/ rather than barium in this configuration was noted. YBa/sub 2/Cu/sub 3/O/sub 7-x/ was formed when diatomic oxygen was used in place of the ozone vapor under nearly identical conditions. The use of pure ozone vapor is the key ingredient in this process, which may be useful in producing thin films of the other high transition temperature compounds.
Properties of in-situ superconducting thin films of Y-Ba-Cu-O on Si, Al/sub 2/O/sub 3/, and SrTiO/sub 3/ substrates

   R.M. Silver, A.B. Berezin, E. Ogawa and A.L. de Lozanne

Summary: The authors report on the as-deposited superconducting properties and microstructure of YBa/sub 2/Cu/sub 3/O/sub 7-y/ thin films grown on Si, Al/sub 2/O/sub 3/ and SrTiO/sub 3/ (110) and (100). They deposited thin films of YBa/sub 2/Cu/sub 3/O/sub 7-y/, which have critical temperatures as high as 68 K, directly on Si. They also grew in situ superconducting films on SrTiO/sub 3/ (110) with critical temperatures of 84.5 K and critical currents typically around 1*10/sup 6/ A/cm/sup 2/ at 4.2 K. Transmission electron microscopy and X-ray diffraction studies showed that the films have a single orientation and no grain boundaries.
Optimization of thin-film YBa/sub 2/Cu/sub 3/O/sub 7/ deposition by DC sputtering onto sapphire substrates

   E.J. Tomlinson, Z.H. Barber, G.W. Morris, R.E. Somekh and J.E. Evetts

Summary: A report is presented on the deposition of YBa/sub 2/Cu/sub 3/O/sub 7/ thin films onto epitaxial magnesia-coated single-crystal sapphire substrates at deposition temperatures in the range of 600 degrees C-850 degrees C. The dependence of film composition on sputtering parameters was investigated using a UHV DC magnetron sputter deposition system with both composite metal and ceramic oxide targets. Films deposited onto epitaxial magnesia are compared to those deposited directly onto sapphire and yttria-stabilized zirconia. The degree of control required for the sputter deposition of YBaCuO thin films at elevated temperatures is shown.
Multiple heteroepitaxy and superlattice formation of LnBaCuO/YBaCuO system

   M. Tonouchi, Y. Yoshizako, M. Iyori and T. Kobayashi

Summary: Multiple heteroepitaxy and superlattice formation of high-T/sub c/ superconducting films were demonstrated. LnBaCuO/YBaCuO structures (Ln=Er, Nd) were realized as a preliminary stage. Superlattice formation made it clear that the crystal structure of the system strongly depends on the substrate materials. A (100)-oriented single-crystal MgO substrate provided a superlattice with the sound perovskite structure, whereas on (110) SrTiO/sub 3/ wafers a deformed crystal was formed. The study of ultrathin YBaCuO film epitaxy revealed that some kind of crystal, deformed from the perovskite structure but not identified yet, was found to grow on SrTiO/sub 3/ wafers regardless of their orientation at the beginning of the deposition, whereas the ultrathin perovskite crystal epitaxially grew on (100) MgO substrate. In addition, MgO thin film epitaxy on NdBaCuO was examined. RHEED patterns revealed that MgO epitaxially grew on both (110) oriented YBaCuO and SrTiO/sub 3/ with the orientation of (100) and (110), respectively.
Comparison of YBa/sub 2/Cu/sub 3/O/sub 7/ films grown by solid-state and vapor-phase epitaxy

   J. Talvacchio, J.R. Gavaler, J. Greggi, M.G. Forrester and A.I. Braginski

Summary: Epitaxial films of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) have been grown on single-crystal SrTiO/sub 3/ and MgO substrates by two different routes using RF and DC magnetron cosputtering. In the first case, amorphous oxide films were deposited at a substrate temperature of 400 degrees C and the crystalline film grew by solid-state epitaxy in an in situ postanneal at approximately 850 degrees C. In the second case, a substrate temperature of 600-650 degrees C was used which was sufficient to crystallize the film as it was deposited from the vapor phase. Reaction with the substrate was less for the films grown by vapor-phase epitaxy-even when they were annealed at 850 degrees C-as shown by the transition temperatures of very thin films, Auger depth profile measurements, in situ XPS analysis, and transmission electron microscopy. XPS was used to show that segregation of Ba at the free surface can occur in either type of film. The relative merits of each growth process are discussed for microwave applications and tunnel junction fabrication.
Single-electron charging effects and implications for tunneling measurements of the high-T/sub c/ superconductors

   J.B. Barner, K. Mullen, M.J. Honkanen, S.T. Ruggiero, E. Ben-Jacob and A.R. Pelton

Summary: A theory is presented for the dynamics of two voltage-biased ultra-small capacitance tunnel junctions connected in series when one or more electrodes are superconducting, and experiments performed on parallel arrays of such junctions are reported. Using the semiclassical model, the authors find that the I-V characteristics display steps and therefore multiple peaks in dI/dV, corresponding to the time-average occupation of the interjunction region by integral numbers of electrons. The voltage at which the first step is located depends on the superconducting gap and the capacitances of the junctions. The spacing between subsequent steps depends solely on the capacitances. A discussion is presented of electron tunneling results performed on metal/Al/sub 2/O/sub 3//2-10 nm-diameter metal particles/Al/sub 2/O/sub 3//metal junctions where this multiple-peak structure is observed. The authors present preliminary tunneling results in junctions using Pb-particles. These results indicate that the multiple-peak structure commonly observed in tunneling data of high-T/sub c/ oxide superconductors can be explained in terms of charging effects in a material with a single superconducting gap.
Magnetic properties and microstructure of sintered high-T/sub c/ Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O oxides

   H. Kumakura, K. Togano, M. Uehara, H. Maeda, K. Takahashi and M. Nakao

Summary: AC complex susceptibility chi '-i chi ", DC magnetization, resistive transition curves in various magnetic fields, and the critical-current density were measured for sintered Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O samples whose major phase was the high-T/sub c/ phase of each system. The single peak observed in chi " vs. temperature curves was very sharp for both samples of each system. The hysteresis in DC magnetization curves at 77 K rapidly decreased with increasing magnetic field for both systems. This may be related to the layered morphology of the platelike grains. The resistive transition curves of both samples were broadened by the application of a magnetic field as in the case of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/. In magnetic fields, rather long tails to low temperatures were observed in resistive transition curves for Bi-Sr-Ca-Cu-O. J/sub c/s at 77 K and zero field were 250 A/cm/sup 2/ and 600 A/cm/sup 2/ for Bi- and Tl-based samples, respectively. These J/sub c/s rapidly decreased with increasing magnetic field.
Preparation of YBa/sub 2/Cu/sub 3/O/sub 7/ powders by molten salt route

   R. Millis, A. Celikkaya, M. Akinc and W. McCallum

Summary: Superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ powders were prepared by using a molten-salt process. Superconducting powders were obtained by heating the molten salt to first solidify, and then to decompose into oxide form. The precursor from copper acetate salt underwent a pyrophoric reaction upon heating while that from copper nitrate required external heating for decomposition. Powders from copper acetate were large ( approximately 10 mu m) and highly porous.
RF magnetron sputtering of Bi-Sr-Ca-Cu-O thin films

   A. Kussmaul, G.M. Roesler Jr., J.E. Tkaczyk, J.S. Moodera, X. Hao, G.A. Gibson, R. Meservey and P.M. Tedrow

Summary: Thin films of the high-T/sub c/ material Bi-Sr-Ca-Cu-O were prepared by the RF-magnetron technique from a single reacted and sintered target in pure argon atmosphere on sapphire substrates. The samples were annealed for three minutes in pure oxygen at 810 degrees C. Their composition was studied by Rutherford backscattering. The superconducting transition was very broad, with R=O at 65 K for the best film. MgO substrates and nonsintered targets were also used. The behavior of the resistance in a magnetic field (up to 20 T) was studied.
Evaluation of grain-coupling strength of YBaCuO superconductors by their magnetic-field profile measurements

   K. Yoshida, T. Kisu, N. Fuchigami and K. Enpuku

Summary: In order to evaluate the strength of intergrain coupling, which determines the transport critical current of polycrystalline oxide superconductors, the relation between the transport critical current and the spatial distribution of the magnetic flux density for YBaCuO thin films as well as bulk superconductors has been studied. The authors have measured the profile of the magnetic flux trapped inside bulk YBaCuO samples with a small Hall magnetic sensor and revealed the correlation between critical-current densities and the slope of the trapped-flux profile, as described by the critical-state model. The measurements of the magnetic-field penetration depth of YBaCuO thin films in a Meissner state is also carried out by measuring the loop inductance of a DC SQUID placed on the YBaCuO thin film to be measured. Observed magnetic-field penetration depths of polycrystalline films with thicknesses of 1-3 mu m deposited on MgO single-crystal substrates amount to approximately 1 mu m for samples with T/sub c/, (end) approximately 80 K and the critical-current density J/sub c/ approximately 10/sup 4/ A/cm/sup 2/ at 4.2 K.
Resistance measurements of high T/sub c/ superconductors using a novel 'bathysphere' cryostat

   J. Moreland, Y. Li, R.M. Folsom and T.E. Capobianco

Summary: A novel cryostat has been developed for variable-temperature testing of high-temperature superconductors. The cryostat is a bathysphere consisting of an overturned stainless steel Dewar suspended in liquid helium. A sample-heater-thermometer assembly is located at the top of the encapsulated (and thermally insulated) vapor space inside of the Dewar. The sample can be rapidly cycled from 300 K to 4 K at an average rate of 1 K/min with a thermal hysteresis of less than 0.1 K. Helium vapor flows through a plug in the bottom of the bathysphere so that pressure of the vapor is roughly ambient. This provides ample heat transfer to and from the sample to maintain thermal equilibrium in the vapor space. Results for resistance versus temperature of some high-temperature superconductors in a magnetic field are presented. Various definitions for thermodynamic and practical T/sub c/s derived from transport resistance measurements are suggested and discussed. These definitions are based on T/sub c/ midpoint, various relative resistance criteria, or absolute resistivity criteria.
Characterization of high T/sub c/ superconductor by luminescence methods

   Y. Fujiwara and T. Kobayashi

Summary: High-T/sub c/ superconductors have been investigated by photoluminescence (PL) and X-ray excited thermally stimulated luminescence (TSL) techniques. Characteristic PLs have been observed in the infrared region in the Er-Ba-Cu-O and Nd-Ba-Cu-O systems, which are tentatively assigned to electronic transitions between weakly crystal-field-split spin-orbit levels of trivalent Er and Nd ions. The spectral shapes and/or peak positions are dependent on the crystal arrangement surrounding the rare-earth ion. Such PLs have never been obtained in the Eu-Ba-Cu-O and Yb-Ba-Cu-O systems. TSL measurements have been performed with particular emphasis on the Gd-Ba-Cu-O system. Characteristic TSLs have been observed in this system, depending on the composition, preparation conditions and cumulative X-ray irradiation time. The activation energy of the related traps ranges from 0.1 eV to 0.3 eV. Characteristic TSLs have also been observed in the Ho-Ba-Cu-O and new high-T/sub c/ superconducting systems containing no rare-earth elements.
Thermal response of copper oxide superconducting thin films

   M.E. Rizkalla and B.G. Burridge

Summary: An analysis of the heat transfer from a current carrying copper oxide superconducting thin film to a copper substrate at 20 K was conducted for the case of a superconducting thin film to be used for high-power switching purposes. The calculations were extended to the maximum operating frequency for a given conduction current. As a result of these calculations, the thermal response time for the thin film due to a pulse heat source has been determined.
Response of YBaCuO thin films to electromagnetic radiation and their electrical characteristics

   A.S. Afanasyev, A.F. Volkov, V.N. Gubankov, Y.Y. Divin and P.M. Shadrin

Summary: An investigation was conducted of the characteristic features of the interaction of electromagnetic radiation with different YBaCuO thin films varying from granular to epitaxial. The current-voltage characteristics and the voltage response of these films to millimeter-wave radiation were measured at temperatures from 4 to 100 K. The behavior of these characteristics for granular and polycrystalline films can be accounted for by a percolation mechanism of conductivity in a two-dimensional system of weak links existing between granulas or grains of the films and having different values of critical currents. It is shown that with the improvement of film structure the mechanism of film interaction with electromagnetic radiation is changed from percolation in the system of weak links between grains to heating in grains of the films.
Complex AC conductance of YBaCuO films

   P.K. Srivastava, P. Debely, H.E. Hintermann, C. Leemann, P. Fluckiger, O. Caccivio, J.-L. Gavilano, J. Weber and P. Martinoli

Summary: The AC linear response of YBaCuO films prepared by RF magnetron sputtering to a small oscillating field was studied as a function of temperature and transverse magnetic field. The structures observed are quite similar to those found in artificially prepared two-dimensional periodic junction arrays where the transition from a phase-ordered to a phase-disordered state at T/sub c/ is attributed to the vortex unbinding mechanism predicted by the Kosterlitz-Thouless theory for phase transitions in two dimensions. The magnetic field data suggest that the typical cell size of the YBCO array is a few mu m, on the order of the grain size. This suggests that the ceramic films can be modeled as two-dimensional networks of Josephson tunnel junctions, the junctions being located at the grain boundaries.
Influence of radiation defects on superconductivity in YBa/sub 2/Cu/sub 3/O/sub 7- delta / films

   A.A. Nikonov, G.V. Sotnikov and A.S. Tokarev

Summary: The influence of 3-3.7-MeV proton bombardment in vacuum media on superconducting properties of Y-Ba-Cu-O films obtained with the aid of pulsed laser deposition on SrTiO/sub 3/ substrates is investigated. It is shown that in the samples investigated T/sub c/ drops linearly with increasing irradiation dose, the rate of this drop is approximately five times quicker than for Nb/sub 3/Sn and there also takes place a broadening of the superconducting transition.
Tunneling spectroscopy in thin films YBCO/Pb tunnel structures

   S. Benacka, V.M. Svistunov, A. Plecenik, S. Chromik, S. Gazi, J. Levarsky, V. Strbik and S. Takacs

Summary: Experimental results on electron tunneling into thin superconducting films of YBa/sub 2/Cu/sub 3/O/sub x/ in YBCO/Pb tunnel junctions are reported. Thin superconducting films of YBCO (thickness 0.7 mu m) were prepared by codeposition of Y, BaO, and Cu onto single-crystal substrates (sapphire, MgO, SrTiO/sub 3/). The maximum critical temperature at zero resistivity was T/sub ce/=85 K. The surface of films is smooth with pancake-shaped grains. The tunnel structure was completed by vacuum deposition of superconducting Pb film (thickness 0.3. mu m) onto YBCO film with either an uncleaned surface or after cleaning in Ar or O/sub 2/ plasma. Two mechanisms are presented which can lead to resonances in the tunneling current of high T/sub c/ superconductors. The first one is caused by geometrical localization of quasiparticles in normal regions in superconducting surroundings in the neighborhood of the counter electrode. It is shown that normal regions of the dimension about 10 nm lead to step distances obtained in experiments. The resonances above the gap can therefore occur not only in grainlike material but also in single crystals and in uniaxially aligned microcrystals with lamellar structure. The second mechanism is based on the model of localized baglike excitations by M. Weinstein (1987).
New Tl-Ba-Ca-Cu-O (1234 and 1245) superconductors with T/sub c/>117 K

   H. Ihara, M. Hirabayashi, N. Terada, M. Jo, K. Hayashi, M. Tokumoto, Y. Kimura, R. Sugise, T. Shimomura and S. Ohashi

Summary: TlBa/sub 2/Ca/sub 3/Cu/sub 4/O/sub 11/ (1234) and TlBa/sub 2/Ca/sub 4/Cu/sub 5/O/sub 13/ (1245) superconductors have been synthesized for the first time. The compounds have T/sub c/ values of 116 approximately 122 K. The highest T/sub c/ value was obtained for the 1234 phase. These are single Tl-O layer compounds with less than half the Tl content of the previous 2223 phase. The structure of the compounds is a simple tetragonal phase with the lattice constants of a=b=3.85 AA and c=19.1 AA for the 1234 phase and a=b=3.85 AA and c=22.3 AA for the 1245 phase. The electron diffraction patterns and the lattice images from a high-resolution TEM have confirmed an oxygen-deficient layered-perovskite structure with the P4/mmm space group. The c-lattice constant follows the c-axis rule of a linear relation of c=6.3+3.2 n (n=the number of Cu-O layers), The T/sub c/ value is strongly related to the valence of Cu ion.
  Author Index (1988)
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