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1990 Part 2     Front Cover (1990 - Part 2)    No author information available Summary: Not available         Table of Contents (1990 - Part 2)     Summary: Not available         A 2-tesla active shield magnet for whole body imaging and spectroscopy    F.J. Davies, R.T. Elliott and D.G. Hawksworth Summary: A 2-T superconducting active shield magnet with a 0.99-m-diameter warm bore for whole-body magnetic resonance imaging (MRI) and spectroscopy has been developed and tested. The magnet and cryostat were designed to meet the same performance standards as existing MRI magnets, but with the volume of the stray field region reduced to less than 4% of that for an unshielded magnet. The 0.5-mT stray field contour is within 5 m axially and 3 m radially of the magnet center. The system weight is only 14 t. The magnet operates at a current of 530 Amps with a stored energy of 9.5 MJ using low cost, high-copper-to-superconductor-ratio conductors on split-construction aluminum formers. The design involved extensive analysis of the stresses in the coils and formers and special consideration of the behavior during quench to avoid burnout or high-voltage breakdown. A low-loss cryostat was also developed with a titanium suspension system and two radiation shields but no liquid nitrogen, the shields being cooled by a single standard Gifford-McMahon refrigerator.         A 4 tesla/1 meter superferric MRI magnet    W.M. Schmidt, F.R. Huson, W.W. Mackay and R.M. Rocha Summary: Superferric technology was first applied to magnetic resonance imaging (MRI) magnets in 1986 with the design and construction of a 4-T/30-cm magnet. In an evolutionary step, this technology is being applied to the development of a whole body 4-T/1-m magnet. The design goals and design parameters of this magnet are presented. The superconductor and spices are discussed, and a passive shimming technique is described.         Superconducting magnet with self-shield for whole body magnetic resonance imaging    Y. Shimada, T. Matsumoto, K. Moritsu, M. Takechi and T. Watanabe Summary: A superconducting magnet has been developed with a self-shield for whole-body magnetic resonance imaging (MRI) that features magnetic field strengths of 0.5 T, 1.0 T, and 1.5 T and has the following characteristics: (1) a low-leakage magnetic field due to the directly mounted magnetic shield (very small in the 0.5-mT range); (2) reduced helium consumption due to the use of a high adiabatic cryostat and refrigerator (does not need liquid nitrogen); (3) a horizontal service port that reduces overhead clearance requirements; (4) superior mechanical strength (can even be transported in the cooled state); and (5) an emergency run down unit.         Design optimization method for a ferromagnetically self-shield MR magnet    M.D. Ogle and J. D'Angelo Summary: A method is described for designing a self-shielded MR (magnetic resonance) magnet. This method determines optimal shielding while maintaining an homogeneous imaging volume. This technique uses the finite-element method in the design iteration loop to solve the magnetic field problem, which includes nonlinear, saturable iron. From the magnetic field solution, the iron magnetization and its contribution to the bore field are determined. The positions and sizes of the current carrying coils are then optimized to obtain the best possible homogeneity. The design iterations are continued until the solutions converge. The iron shield design can also be modified at any iteration if further optimization of the iron shield is required.         Magnetic shielding for MRI superconducting magnets    A. Ishiyama and H. Hirooka Summary: An optical design is presented of a highly homogeneous superconducting coil system with magnetic shielding for magnetic resonance imaging (MRI). The optimal design method is a combination of the hybrid finite-element and 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 multiobjective goal programming method and the nonlinear least-squares method are adopted. The optimal design results of 1.5- and 4.7-T-magnet systems with different types of magnetic shielding for whole-body imaging are compared, and the advantages of a combination of active and yoke shields are shown.         Optimized configurations for actively shielded magnetic resonance imaging magnets    A.K. Kalafala Summary: A unique design approach based on the multistage Monte Carlo method is suggested. It allows for a thorough search for optimized designs within the bounds of the multidimensional design space created by the competing requirements and imposed spatial restrictions. This design space is shown to contain a multiplicity of different coil configurations, each processing a sharply defined minimum in the resulting stray field level, field inhomogeneity, or amount of conductor. Optimization techniques that depend on local gradients would tend, in such a case, to be trapped in the many local minima and fail to locate a global minimum. Several examples are discussed to highlight the advantages of the proposed design approach.         Protection system for inductively coupled magnets (and experience in MRI magnet systems)    R.E. Schwall Summary: A completely passive protection system for complex assemblies of superconductive magnets is presented. Quench-back heaters are used to initiate normal zones in multiple coils. Silicon diodes operating at 4.5 K are utilized to permit rapid charging and discharging of the magnet system, to protect the persistent current switches, and to prevent the long-lived field disturbances associated with resistively shunted magnets. Protection modules employing a self-limiting heater are used to provide the rapid response necessary to protect inductively coupled shim coils while maintaining protection system integrity during a worst-case quench of the main coils. Operating experience with this protection technique on three Magnetic Resonance Imaging (MRI) magnet systems is reported.         Test results from the SMES proof of principle experiment    J.M. Pfotenhauer, M.K. Abdelsalam, F. Bodker, D. Huttleston, Z. Jiang, O.D. Lokken, D. Scherbarth, B. Tao and D. Yu Summary: A proof-of-principle experiment (POPE) has been conducted to demonstrate the stability and operation of the superconducting magnetic energy storage (SMES) conductor in an engineering test model (ETM) design. The experimental facility includes: a 100-kA DC power supply; a 4-T, 1-m bore, background field split solenoid: a three-turn-1-m-diameter test coil for the ETM conductor; a dewar for operation of the solenoid and test coil, at 1.8 K and 1 atm; and support systems for vacuum, helium supply and recovery, and data acquisition. The test facility exactly duplicates the electric, magnetic, and thermal conditions expected for the ETM conductor. A report is presented on measurements of conductor stability vs. transport current, applied magnetic field, and cooling from liquid helium. The measurements characterize the conductor's stability against finite-length traveling normal zones and against quenches resulting from transient normal zones. The data qualify the conductor for dependable use at 50 kA, 4 T, and 1.8 K.         Structural considerations and analysis results for a large superconducting magnetic energy storage device    J.T. Dederer, R.J. Hillenbrand, D.T. Hackworth and X. Haung Summary: A description of the conceptual design for the magnet structure of a large superconducting magnetic energy storage (SMES) device is presented. This work is part of a program to select the best design for a 21-MWh unit. The coil structure is a four-layer solenoid design with a mean radius of 219 ft and carries a current of 50000 A. The structure design selected and the tradeoffs among different geometries are described. The results of a parametric finite-element and closed-form stress analysis are given in order to compare different rippled coil geometries in terms of structure stresses and cyclic conductor strain. The effects of ripple radius and strut spacing are given for the cooldown, normal operation, and quench conditions.         Key design selections for the 20.4 MWh SMES/ETM    R.J. Loyd, T.E. Walsh and E.R. Kimmy Summary: The 20.4-MWh superconducting magnetic energy storage engineering test model (SMES/ETM) will be the world's largest superconducting magnet by nearly two orders of magnitude in stored energy. Its size, Lorentz loads, and power delivery requirements dictate a number of fundamental design requirements. In addition, the SMES/ETM must fully accomplish its primary mission of demonstrating large-scale SMES technology, while at the same time minimizing technical, schedule, and cost risks. A discussion is presented of nine key design decisions that are fundamental to meeting these challenging goals. These are a conductor current of 200 kA, helium containment within the conductor, an operating temperature of 1.8 K, a CICC conductor with a hollow core, a conductor premanufactured in half-turn lengths, a circular and continuous coil pac structure, fiberglass-reinforced plastic pultrusion for the coil pack structure material, a coil pack operating position that is precompressed radially inward, and a liner for vacuum enclosure.         Coil protection for the 20.4 MWh SMES/ETM    R.J. Loyd, A.M. Bulc and C.L. Chang Summary: The 20.4-MWh superconducting magnetic energy storage engineering test model (SMES/ETM) is large and stores nearly two orders of magnitude more energy than any man-made magnet to date. These characteristics pose unique requirements for coil protection in response to a normal zone. A method of detecting a normal zone, action taken to quench the coil, and the subsequent temperature and voltage response of the coil pack are presented. It is shown that a normal zone produces a significant resistive voltage that can be easily detected, the coil is driven normal at half-turn intervals by inductive heaters, and coil response is calculated to be benign, both thermally and electrically.         Coil pack design for the 20.4 MWh SMES/ETM system    D.L. Walker, R.C. McCool and D.C. Rix Summary: The conceptual design of an engineering test model (ETM) of a superconducting magnetic energy storage (SMES) system that will demonstrate the efficacy of large scale production systems is described. Large-scale SMES systems are likely to store 1000 to 10000 MWh of electricity in a solenoid winding 300 to 1500 m in diameter. The conceptual design of the ETM coil pack is presented. The design approach taken to reduce technical risk has been to aim at simplicity, to avoid unproven manufacturing methods, to apply conservative safety factors when establishing design allowables, and to develop and test to prove efficacy.         Test results from the 200 kA SMES/ETM conductor    S.D. Peck and P.H. Michels Summary: The critical current and stability margin of a 200-kA, copper-stabilized, cable-in-conduit conductor cooled with helium-II have been measured. The test specimen was 3 m long, inserted in a uniform background dipole field of up to 5 T with an effective length of 0.9 m. The critical current of the conductor was measured at 1.8 K and found to be 280 kA at a total field of 5.8 T, 260 kA at 6.4 T, and 215 kA at 7.4 T. Normal zones of 2-cm initial length were initiated by inductive heaters, and the voltage and temperature of the conductor in the heated zone were monitored for recovery of propagation. The stability margin is reported as a function of the current density over the cable space at various background fields, bath temperatures, heated lengths, heater pulse durations, and numbers of cumulative load cycles. The test results demonstrated that the conductor can operate at 200 kA in the Engineering Test Model for SMES where the peak total field is 4.13 T.         Superconducting magnet system for HERA    R. Meinke Summary: The HERA accelerator facility consists of independent accelerators designed to store respectively 820-GeV protons and 30-GeV electrons. The two counterrotating beams collide head on in up to four interaction regions, which are distributed uniformly around the accelerator circumference of 6336 m. In the arcs of the ring the protons are guided and focused by some 650 superconducting dipole and quadrupole magnets and more than 1500 superconducting correction coils. In the straight sections around the intersection points the proton beam is guided by about 120 normal conducting magnets.         The superconducting magnet system for the LHC    R. Perin Summary: The new facility for the Large Hadron Collider (LHC) will mainly consist of a 27-km-long double ring of high-field superconducting magnets installed in the Large Electron-Positron Collider (LEP) tunnel, above the LEP machine components. The magnet system comprises nearly 2000 twin-aperture, 8-10-T, 10-m-long, dipole bending magnets, more than 500 250-T/m, twin-aperture quadrupoles, and a very large number of other superconducting magnetic components. A general description of the system is given together with the main features of the design of the regular lattice magnets. Also described is the present state of the magnet R&D program, which, after the successful phase of short model magnets, is now aimed at the construction of a full prototype 100-m-long cell for the LHC machine.         Design, fabrication, and test of a 5-cm aperture, 1-m long superconducting dipole prototype for high energy Hadron collider    T. Shintomi, T. Ogitsu, A. Terashima, K. Maehata, M. Wake, H. Hirabayashi and A. Devred Summary: A 1-m-long superconducting dipole prototype with an aperture of 5 cm and a rated field of 6.6 T was built and tested. This model was based on a two-layer cosine-theta coil clamped by stainless steel collars inside a laminated iron yoke, with a large keystone-angle cable and no wedge. The cold mass was encased in an outer stainless steel skin. The magnet was instrumented with voltage taps, which allow the location of the quench start, and with strain gauges, which allow the measurement of the coil stress variations during assembly, cool-down, and energization. Prior to the assembly, several tests were carried out in order to understand the mechanical properties of the coil and to determine a proper calibration for the strain gauges. A report is presented on the design studies, with emphasis on the calibration problem, followed by a discussion of the magnet assembly and quench performance in light of the mechanical measurements.         Evaluation of the production of a short twin-aperture dipole magnet for LHC from an industrial point of view    F. van Overbeeke, R.L. Dubbeldam and H.J. Israel Summary: A discussion is presented of the experience gained during the production of a 1-m-long, twin-aperture, 10-T dipole magnet for the Large Hadron Collider (LHC) magnet development program of CERN. The experience consists partly of technical solutions and partly of special attention items. Also discussed are the two main tooling items: the winding machine and the curing and collaring press. The fabrication process is outlined, along with aspects of project management.         A statistical evaluation of recent SSC conductors produced at IGC/ASI    P. Valaris, H.C. Kanithi, R. Macri and B.A. Zeitlin Summary: One of the requirements for uniform field quality in the SSC (Superconducting Super Collider) dipole magnets is the consistency in the superconducting strand characteristics from start to finish to the production phase. As full-scale production of strand and cable approaches, the consistency in performance of the early batches of conductor needs to be examined. A number of 300-mm billets have been manufactured with tight process controls. The performance of the final conductor in terms of piece lengths, current density, Cu/Sc ratio, and wire diameter has been evaluated. The data are analyzed in order to understand the variations that are related to the conductor design and processing. The current density of the strand is examined over the length of the billet to determine inherent variability in the NbTi alloy itself.         A new internal tin Nb/sub 3/Sn conductor made by a novel manufacturing process    G.M. Ozeryansky and E. Gregory Summary: A novel variation of the internal tin method which improves upon the conventional approach is described. It offers promise as a way of producing reliable and economical Nb/sub 3/Sn for high-energy physics, fusion, and other applications. Preliminary results show several important advantages over the conventional internal tin and bronze approaches. These include improved filament arrays and low distortion, which allow the introduction of high percentages of niobium alloy filaments without the occurrence of bridging. As a result the material is expected to exhibit high J/sub c/'s with low losses. In addition the new process is less complicated than the conventional approach and produces a reliable economical product in relatively long piece lengths.         Upper critical fields and critical current densities in bronze processed commercial multifilamentary Nb/sub 3/Sn wires    K. Watanabe, K. Noto and Y. Muto Summary: The T/sub c/, B/sub c2/, and J/sub c/ were investigated for superconductors in a residual strain state for bronze processed commercial multifilamentary Nb/sub 3/Sn wires. It was found that the temperature dependence of B/sub c2/ under strain obeys (1-(2/3)( pi T/1.75T/sub c/)/sup 2/) near T=0 and (1-T/T/sub c/) near T/sub c/. The establishment of the temperature scaling law of a global pinning force F/sub p/=J/sub c/*B was confirmed in commercial Nb/sub 3/Sn wires.         A characterization of internal-Sn Nb/sub 3/Sn superconductors for use in the proof of principles (POP) coil (for ITER)    L.T. Summers, A.R. Duenas, C.E. Karlsen, G.M. Ozeryansky and E. Gregory Summary: High-performance, Ti-alloyed, internal-Sn superconductors have been selected for use in the Proof of Principles (POP) coil, a 1.0-m o.d., 0.4-m i.d. solenoid designed to produce fields up to 15 T. The POP coil will use forced-flow cable-in-conduit conductors (CICC) and will operate at 4.2 K and moderate levels of conductor strain. A report is presented on the results of detailed characterizations of two proposed POP coil Nb/sub 3/Sn 19 subelement superconducting wires of differing topology. An investigation has been conducted of the critical current as a function of applied field and applied strain. The wires were found to have excellent high-field properties, providing a high performance margin for the proposed POP coil. The field and strain dependence of J/sub c/ have been found to compare favorably with predictions from a wire performance model recently developed for Nb/sub 3/Sn superconductors.         Critical currents of Nb/sub 3/Sn wires for the US-DPC coil    M. Takayasu, C.Y. Gung, M.M. Steeves, M.O. Hoenig, J.R. Hale and D.B. Smathers Summary: The critical current of titanium-alloyed internal-tin, jelly-roll Nb/sub 3/Sn wire for use in the US Demonstration Poloidal Coil (US-DPC) was evaluated. It was confirmed from 14 randomly-selected samples that the critical-current values were uniform and consistent: the noncopper critical-current density was approximately 700 A/mm/sup 2/ at 10 T and 4.2 K, in agreement with expectations. A 27-strand cable-in-conduit conductor (CICC) using the low-thermal-coefficient-of-expansion superalloy Incoloy 905 yielded a critical current 5-7% below the average value of the single-strand data.         Dependence of critical current densities in composite conductors with ultrafine filaments on the magnetic field application    Y. Kubota, T. Ogasawara, S. Ban, M. Chiba, N. Miyazawa, K. Yasohama and H. Kobayashi Summary: Critical current densities of Nb/sub 3/Sn composite conductors with ultrafine filament (d/sub f/=36.7 nm approximately 145 nm) have been observed to depend on the magnetic history of the composite. Magnetic fields were applied as follows. (A) (1) The bias field is increased to higher values and then reduced to B/sub 0/, (2) the bias field is increased directly from zero to B/sub 0/; and (3) the composite is cooled down within B/sub 0/. (B) After establishing B/sub 0/, a second field B/sub m/ is temporarily superimposed parallel or antiparallel to B/sub 0/ and then removed. Then the critical current density is measured by increasing the current. A new cycle of B/sub m/ of the same sign may follow, with the process being repeated.         Development of 10 kA class Nb/sub 3/Al superconducting cable by jelly-roll process (for fusion magnets)    T. Ando, Y. Takahashi, M. Nishi, Y. Yamada, K. Ohmatsu and M. Nagata Summary: A multifilamentary Cu/Nb/sub 3/Al composite strand was developed with a noncopper critical current density of more than 400 A/mm/sup 2/ at 12 T, by a jelly-roll process. A 10-kA cable-in-conduit conductor was fabricated to demonstrate its applicability to fusion magnets. The cable had 324 strands, and a circular CuNi seamless pipe was used as the conduit. The strand diameter was 0.88 mm and the filament diameter was 28 mu m. The heat treatment was performed at 820 degrees C for 2 h.         Improved Sn/sub 1.2/Mo/sub 6/S/sub 8/ wire preparation technique    W. Goldacker, G. Rimikis, E. Seibt and R. Flukiger Summary: Enhanced techniques of preparing cold-worked Sn/sub 1.2/Mo/sub 6/S/sub 8/ wires with Ta and Nb barriers led to increased critical current densities of J/sub c/ (4.2 K)=1*10/sup 4/ A-cm/sup -2/ and J/sub c/ (1.8 K)=2.5*10/sup 4A/cm/sup -2/ in a magnetic field of 20 T. In addition to the application of different powder purification methods, a series of quite different wire preparation techniques was performed. As starting materials either an unreacted powder mixture or a HIP prereacted Chevrel phase material with different contents of reacted phase was used. The final annealing of the wires was performed conventionally and under HIP conditions to test the densification of the Chevrel phase filaments. Both possible barrier materials, Ta and Nb, were used and compared with respect to the workability, the chemical reaction with the Chevrel phase filament during the final annealing, and the resulting prestress state in the filament.         Development of conductors for superconducting generators    T. Ogawa, K. Uyeda, K. Takahashi, T. Saito, Y. Tanaka, M. Nagata, O. Kono, K. Kamata and H. Taniguchi Summary: Basic design studies are conducted for 7-MVA superconducting generators, and superconductors are developed. For generators, it is intended to develop a slow-response-excitation-type generator with emphasis placed on stability and higher current density, and a quick-response-excitation-type generator with reduction of AC loss for enhancing the excitation speed. Three kinds of NbTi field windings for these superconducting generators were designed and developed with targets set for the conductor size, critical current, AC loss, void fraction, etc. The development of a conductor processing technique, improvement of the heat treatment technique, and development of a composite stranded wire technique were pursued. For Nb/sub 3/Sn conductors, research was conducted to enhance the current density of strands and their workability by a bronze process and an in situ process.         Design, fabrication, and properties of magnetically compensated SSC strands    E.W. Collings, K.R. Marken Jr., M.D. Sumption, G. Iwaki and S. Sakai Summary: The addition of Ni to a superconducting strand can compensate its diamagnetic persistent-current magnetization over a portion of the beam-injection and acceleration stroke of the Superconducting Super Collider (SSC) magnet. The ferromagnetic addition may thus relieve the SSC magnet's need for extremely fine filaments, the initial purpose of which was to minimize conductor magnetization. It is shown how the Ni could be incorporated into the strand itself, either in the form of replacement filaments or as a coating on the outside surface.         Eddy-current effects in twisted and wound SSC strands    K.R. Marken Jr., A.J. Markworth, M.D. Sumption, E.W. Collings and R.M. Scanlan Summary: An analysis has been made of the effective pitch (with respect to an applied field transverse to the winding axis) of a pair of filaments that have been first twisted and then helically wound. In case of very different values of twist pitch and winding pitch, the effective pitch is simply the smaller of these. However, as the value of the winding pitch approaches that of the twist pitch, the effective pitch may become quite large. Results of this analysis are compared with magnetization measurements of a series of helically wound strands with varied twist pitch. These measurements show large eddy-current losses in a twisted strand with a twist pitch comparable to the winding pitch; more generally, it is shown that eddy-current loss depends upon the superposition of twist and winding. The general shape of the magnetization as a function of applied field M(H) loop due to the combined effects of filamentary hysteresis and eddy currents has been mathematically modeled.         Hall probe magnetometer for SSC magnet cables: effect of transport current on magnetization and flux creep    R.W. Cross and R.B. Goldfarb Summary: A Hall probe magnetometer has been constructed to measure the magnetization hysteresis loops of Superconducting Super Collider magnet cables. The instrument uses two Hall-effect field sensors to measure the applied field H and the magnetic induction B. Magnetization M is calculated from the difference of the two quantities. The Hall probes are centered coaxially in the bore of a superconducting solenoid with the B probe against the sample's broad surface. An alternative probe arrangement, in which M is measured directly, aligns the sample probe parallel to the field. M was measured as a function of H and field cycle rate both with and without a DC transport current. Flux creep as a function of current was measured from the dependence of AC loss on the cycling rate and from the decay of magnetization with time. Transport currents up to 20% of the critical current have a minimal effect on magnetization and flux creep.         SSC type NbTi superconductor research program at Teledyne SC    J.F. Kallsen, W.K. McDonald, J.D. Geno, P.M. O'Larey and M.B. Siddall Summary: In an ongoing research effort, several multifilament niobium titanium composite billets have been fabricated and processed to make SSC (Superconducting Super Collider) wire. Critical current densities of 3000 A/mm/sup 2/+or-5% and 2950 A/mm/sup 2/+or-5% (5 T, 4.2 K, 10/sup -14/ Omega -m) have been achieved in wires containing 6.5- and 4.8- mu m-diameter filaments, respectively. Piece length and suitability for cable are addressed.         Further development of aluminum clad superconductors    H.C. Kanithi, D. Phillips and B.A. Zeitlin Summary: A high-volume fabrication technique has been developed to clad conventional NbTi/Cu composite conductors with high-purity aluminum. A variety of sizes and shapes of practical superconductors has been clad using aluminum of initial residual resistance ratios ranging from 200 to 3000. In some of the conductor configurations a strengthening element in the form of a stainless steel wire or an aluminum alloy has been incorporated. The various conductor types investigated and their mechanical and electrical characteristics are presented. The advanced conductors developed will be particularly suitable for large magnet applications such as high-energy physics particle detectors, high-field MRI, and magnetic energy storage.         Development of scaling rules for Rutherford type superconducting cables    J.M. Royet and R.M. Scanlan Summary: Scaling rules that provide guidelines for choosing the parameters for a wide range of superconducting cables are given. These parameters include strand size, strand number, keystone angle, percentage of compaction, cable pitch, and compacted cable dimensions. In addition, the tolerance ranges for the key cable manufacturing parameters such as mandrel size and shape, strand tension, and Turkshead temperature control are defined. Results on cables ranging from 8 strands to 36 strands of 0.65-mm wire and from 8 strands to 30 strands of 0.8-mm wire are presented. These results are used to demonstrate the application of the scaling rules for Rutherford-type cable.         Effect of mechanical deformation on Nb-Ti filament proximity-effect coupling at the edges of SSC cables    T.W. Petersen and R.B. Goldfarb Summary: Magnetization as a function of transverse magnetic field and time was measured for short strands extracted from the centers and edges of five Nb-Ti Rutherford cables designed for use in Superconducting Super Collider dipole magnets. The multifilamentary strands all had 6- mu m-diameter filaments. Edge samples, which had severe mechanical deformation, showed small magnetic coupling losses at low fields, compared to no coupling losses for underformed center strands. The existence of sharp strand bends at cable edges decreases the interfilament spacing to the order of the coherence length in the normal matrix material, which increases the effective filament diameter and hysteresis loss at low fields. Microscopic studies of the cables' cross sections confirmed smaller interfilament separations in these samples. Flux creep measurements, represented by the time dependence of magnetization, showed little difference between edge and center samples.         Measurement of time dependent fields in high gradient superconducting quadrupoles for the Tevatron    M.J. Lamm, K. Coulter, S. Gourlay and T.S. Jaffery Summary: Magnetic field measurements have been performed on prototype and production magnets from two high-gradient superconducting quadrupole designs. One design is a double-shell quadrupole with 36-strand Rutherford cable. The other design is a single-shell quadrupole with five individually insulated monolithic strands connected in series. These magnets have similar bore diameters and cable dimensions. However, there are significant differences between the two designs, as well as differences between prototype and production magnets within each design, with regard to Cu-to-superconductor ratio, filament diameters, and filament-spacing-to-strand-diameter ratio. The time dependence at fixed currents of the measured magnetic field is discussed.         Degradation studies of Fermilab low beta quadrupole cable    S.A. Gourlay, M. Garber, J. Royet and R.M. Scanlan Summary: The production of high-gradient superconducting quadrupoles for the Tevatron D0/B0 low-beta insertion is currently underway. The two-shell design utilizes a 36-strand Rutherford-style cable. A measure of cable quality is given by a comparison of the critical current of the cable with the sum of the critical currents of the strand. A recent study involving variations in the cabling conditions and dimensional parameters has resulted in a significant decrease in degradation. Over the period of cable production degradation has been reduced from an average 12% to less than 4%. Some cable samples measured exhibit J/sub c/'s in excess of 3100 A/mm/sup 2/ at 5 T. The adjustments to the cabling procedure which are believed to be responsible for the reduction in J/sub c/ degradation are discussed.         Critical current of prototype conductors for LHC dipole magnets    P. Fabbricatore, R. Musenich, R. Parodi, D. Truffelli and G. Zappavigna Summary: Electrical measurements on conductors developed for Large Hadron Collider (LHC) dipole magnets are reported. Two kinds of measurements were carried out: critical current on the prototype cables and AC magnetic measurements on the strands. To perform critical current measurements the samples were placed in the bore of the superconducting magnet MARISA, which allows measurements up to 6.5 T while temperature ranges from 1.8 to 5 K. The current is supplied using an inductive method: the background magnet is the primary winding of a transformer having the sample as a secondary winding. The current is measured by Hall probes placed near the samples; the critical current is measured by the resistive criterion rho =10/sup -14/ Omega m. Critical currents up to 60 kA were measured for four different samples. AC magnetic measurements, like AC susceptibility and penetrated and trapped magnetic flux, were carried out in order to study the connections between the critical current and the effective critical field. Information about the filament coupling at low field is also obtained.         Development of NbTi based cables for LHC dipoles    H.G. Ky, G. Grunblatt and P. Bonnet Summary: The technology developed to meet LHC (Large Hadron Collider) dipole superconductive cable requirements is discussed. The program carried out includes the development of a 5- mu m NbTi filament, high J/sub c/ and low-magnetization elementary strands for high-field applications, and the manufacture of large compacted keystone cables. Characteristics of the NbTi strands and cables manufactured are presented, as well as test results performed at 4.2 K and below for magnetic field up to 11 T.         The effect of static and cyclic axial strain on I/sub c/ of cable in conduit net subcables    W. Specking, M. Klemm, R. Flukiger, P. Bruzzone and M. Ricci Summary: The effect of static and cyclic axial strain, in /sub a/, on the critical current, I/sub c/, of Nb/sub 3/Sn cable in conduit (CIC) subconductors has been measured at I/sub c/         The transverse stress effect on the critical current of jelly-roll multifilamentary Nb/sub 3/Al wires    D. Zeritis, Y. Iwasa, T. Ando, Y. Takahashi, M. Nishi, H. Nakajima and S. Shimamoto Summary: Experiments were conducted to determine the effect of transverse compressive stress (TCS) on the critical current of jelly-roll multifilamentary Nb/sub 3/Al wire (0.8-mm dia.) for magnetic flux densities up to 12 T. For comparison, identical experiments were performed for bronze-process Ti-alloyed multifilamentary Nb/sub 3/Sn wire (1.0-mm dia.). Although the unstressed critical current density of Nb/sub 3/Al was inferior to that of (NbTi)/sub 3/Sn at high fields, under applied TCS Nb/sub 3/Al exhibited less critical current degradation than (NbTi)/sub 3/Sn. For example, at 12 T and 150 MPa. TCS-induced critical current degradation was approximately 20% for Nb/sub 3/Al, whereas it was approximately 65% for (NbTi)/sub 3/Sn.         The effect of transverse loads up to 300 MPa on the critical currents of Nb/sub 3/Sn cables (for LHC)    H. Boschman, A.P. Verweij, S. Wessel, H.H.J. ten Kate and L.J.M. van de Klundert Summary: In the framework of the development of an experimental 10-T Nb/sub 3/Sn dipole coil for the LHC (Large Hadron Collider) at CERN, the effects of transverse stress on Rutherford-type Nb/sub 3/Sn cable were investigated. For this purpose a special facility was designed and put into operation in which the voltage-current behavior of short pieces of Nb/sub 3/Sn cables can be investigated in a background field of up to 11 T and an applied stress of 300 MPa. The repulsive Lorentz force of 250 kN, generated by a set of superconducting coils, is used to impress the cable over an area of 20*42 mm/sup 2/ maximum, in the presence of a transport current of up to 40 kA. The testing equipment is described, and the first results of the observed critical current degradation of two Nb/sub 3/Sn cables are discussed.         FENIX, a test facility for ITER and other new superconducting magnets    D.S. Slack, R.E. Patrick and J.R. Miller Summary: The Fusion Engineering International Experimental (FENIX) Test Facility is a 76-t set of superconducting magnets housed in a 4-m-diameter cryostat. It represents a significant step toward meeting the testing needs for the development of superconductors appropriate for such large-scale magnet applications as the International Thermonuclear Experimental Reactor (ITER). The magnet set is configured to allow radial access to the 0.4-m-diameter high-field region where maximum fields of up to 14 T will be provided. The facility is fitted with a thermally isolated test well with a port to the high-field region that allows insertion and removal of test conductors without disturbing the cryogenic environment of the magnets. Its general design features, construction, and capabilities are discussed.         Critical current measurements using 13-T split coils and 100-kA superconducting transformer (for FER)    T. Isono, Y. Takahashi, K. Yoshida, K. Okuno, N. Koizumi, M. Sugimoto, M. Nishi, H. Nakajima, T. Hiyama, T. Kato, K. Kawano, H. Hiue, M. Ono, E. Kawagoe, H. Ishida, J. Yoshida, Y. Kamiyauchi, M. Oshikiri, H. Hanawa, H. Ohuchi, T. Ohuchi, F. Tajiri, T. Hosoya, N. Watahiki, T. Ando, H. Tsuji, M. Konno, T. Uede, I. Itoh, K. Sakaki, N. Aoki and E. Suzuki Summary: A description is given of a large scale superconductor test facility composed of a 13-T magnetic field and a 100-kA sample current. A superconductor transformer with a 100-kA secondary conductor was fabricated as a current amplifier in order to supply the 100-kA sample current. Superconducting split coils with 100-mm clear bore diameter were fabricated, and a 13-T available field was generated by these coils. Both the 100-kA superconducting transformer and the 13-T superconducting split coils were installed in a 2-m-diameter FRP dewar for the purpose of testing large-scale superconductors. A description is given of the performance of the 100-kA superconducting transformer and the 13-T superconducting split coils as well as the results from critical current measurements of prototype conductors for toroidal coils.         Superconducting current transducer (for cable testing facility)    M. Kuchnir and J.P. Ozelis Summary: The construction and performance of an electric current meter that operates in liquid He and mechanically splits apart to permit replacement of the current carrying conductor are described. It permits the measurement of currents induced in a loop of superconducting cable and expeditious exchange of such loops. It is a key component for a short sample cable testing facility that requires no high-current power supplies or high-current leads. Its superconducting pickup circuit involves a nonmagnetic core toroidal split-coil that surrounds the conductor and a solenoid whose field is sensed by a Hall probe. This toroidal split-coil is potted inside another compensating toroidal split-coil. Currents of up to 10 kA can be measured with a precision of 150 mA.         Electrical properties of superconducting joint between composite conductors    T. Tominaka, S. Kakugawa, N. Hara and N. Maki Summary: To investigate the electrical properties of the joint between superconducting multifilamentary wires, the authors used a radio-frequency superconducting quantum interference device (RF-SQUID) voltmeter to measure the extremely small voltage induced across the joint. They measured the time variation of both the current induced in a loop of superconducting wire and the voltage induced across the joint. A voltage sensitivity in the picovolt range was obtained with this apparatus. Comparisons of current decay between superconducting loops with soldered, spot-welded and cold-welded joints were made. A flux-creep-like phenomenon was seen in the current decay for the cold-welded and spot-welded joints.         Superconducting cable joint resistance    O. Herbelot, M.M. Steeves and M.O. Hoenig Summary: Results of a parametric study of the 4.2-K resistance of lap joints between two 27-strand cables of multifilamentary Nb/sub 3/Sn wire are reported. All joints were between ribbon terminations made by rolling copper-encapsulated cable ends flat. Resistances as functions of current were inferred from current decay time constants of cable-in-conduit conductor loops connected by the joints. The resistances of 23 samples were measured (range of 0.2 to 3 n Omega ). It was found that lap joint resistance was a function of current. The influences of solder versus no solder, solder thickness, indium versus tin-lead, ribbon surface oxidation, solder flux, cable twist pitch, wire chrome plating, clamping pressure during heat treatment, ribbon aspect ratio, and joint length are reported.         Superconducting current leads of YBCO and Pb-BSCCO    D.U. Gubser, M.M. Miller, L. Toth, R. Rayne, S. Lawrence, N.M. Alford and T.W. Buttons Summary: The authors fabricated and measured cylindrical superconducting current leads composed of a Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ (YBCO) and Bi/sub 2-x/Pb/sub x/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/ (Pb-BSCCO) that were approximately 20 cm long and 1 cm/sup 2/ in cross section. A steady-state, DC, critical current of 170 (230) A at a temperature of 77 K was measured for YBCO (Pb-BSCCO) using a voltage criterion of 2*10/sup -7/ V ( rho =8*10/sup -10/ Omega -cm). This current was limited by the current-induced self-magnetic field. At a temperature of 63 K this current increased to approximately 390 (465) A. The character of the magnetic field dependence of the critical current and shape of the current-induced voltage curves are different for the two materials.         High temperature superconducting current leads for cryogenic applications in moderate magnetic fields    B. Dorri, K. Herd, E.T. Laskaris, J.E. Tkaczyk and K.W. Lay Summary: Large YBa/sub 2/Cu/sub 3/O/sub 7- delta / ceramic conductors suitable for bulk current applications have been fabricated using a magnetic technique to generate c-axis grain alignment. Critical currents on the order of several hundred amperes in a background field of 0.1 T have been achieved as a result of the aligned microstructure. The unusual dependence of the critical current on temperature and magnetic field is discussed in the context of anisotropy, self-field, and hysteretic effects.         Design and testing of a high temperature superconducting current lead    J.L. Wu, J.T. Dederer, P.W. Eckels, S.K. Singh, J.R. Hull, R.B. Poeppel, C.A. Youngdahl, J.P. Singh, M.T. Lanagan and U. Balachandran Summary: The high critical temperature and low thermal conductivity of the ceramic superconductor Y-Ba-Cu-O were utilized to reduce the Joule heating and the heat leak in a vapor-cooled current lead design of nominally 1-kA capacity. The lead consists of a lower superconducting part and an upper normal metal (copper) part. The superconducting part is an assembly of 20 rectangular bars fabricated from a composite of Y-Ba-Cu-O and Ag (15% vol.). This part is designed to operate below the critical temperature of the ceramic superconductor. The copper part, consisting of 20 copper wires, extends outside of the cryostat and interfaces to the room-temperature power supply. The lead was successfully tested in a liquid-helium cryostat for currents up to 2 kA. At the optimum operating currents of 1.7-1.8 kA, the helium boil-off measurements show heat leak reduction of approximately 40% from the conventional designs. Details of the design, fabrication issues, and the testing are presented.         YBaCuO current lead for liquid helium temperature applications    F. Grivon, A. Leriche, C. Cottevieille, J.C. Kermarrec, A. Petitbon, A. Fevrier and Y. Laumond Summary: A study was made of the losses of a double current lead (copper from 300 K to 77 K and YBaCuO from 77 K to 4.2 K). The authors give the main results obtained: (1) on the value of 1/J/sub c/ integral /sub 4.2/ /sub K//sup 77/ /sup K/KdT, (2) on the electrical contact resistance between YBaCuO and metal, (3) on the transport critical current density and 50-Hz losses of sintered tubes and textured material, and (4) on a 1-kA double DC current lead. On the basis of these results, it seems possible to decrease the current lead losses by a factor of 5.         An explosive opening superconducting switch    T.L. Francavilla, R.D. Ford, W.H. Lupton, N.M. Alford and C.S. Saunders Summary: A superconducting YBCO tube was tested as an opening switch to demonstrate novel switching concepts for inductive energy storage. The tube was connected in series with a 1.2-mH inductor and a 4800- mu F capacitor bank which was charged to a predetermined level and discharged through the circuit. No measurable dissipation was observed for test discharges of 8-ms duration, with maximum pulse amplitude increasing for each test while the YBCO was superconducting at 77 K. At the highest current pulse maximum of 95 A, the switch was opened by exploding a short length of detonating cord inserted into the center of the tube. The current decreased to zero, and the voltage increased to maximum in approximately 160 mu s, resulting in a voltage gain of over 25 for current commutation purposes.         Characteristics of YBaCuO magnetic shields    M.J. Hurben, O.G. Symko, W.J. Yeh, S. Kulkarni and M. Novak Summary: Magnetic shielding properties of YBaCuO tubes have been studied at temperatures of 77 K and 4 K. Shielding effectiveness was determined by measuring the magnetic field inside the tube in the presence of external magnetic fields. A high degree of shielding was achieved up to a critical external field determined by the critical current density of the material. Typically, this critical field is 23 Oe at 77 K extending up to 105 Oe at 4 K. Tubes made with material containing 10% silver exhibited much stronger flux pinning behavior when the external magnetic field started to penetrate the tubes. The tubes studied were effective in shielding a RF-biased SQUID (superconducting quantum interference device) for operation at 77 K.         Evaluation of solders for superconducting magnetic shield    K. Seo, S. Nishijima, K. Katagiri and T. Okada Summary: A magnetic shield with a superconducting winding has been studied aiming at the practical application of the shield in a magnetic field of higher than 3 T. Tubular magnetic shields have been fabricated with superconducting windings using NbTi multifilamentary composite wires. The shields were impregnated with two kinds of solders (Wood's metal and indium) to make the electric joint between the wires. In spite of the fact that the superconducting wire provides enough performance to shield the external field of 4 T (I/sub c/=225 A at 4 T), the maximum shielded field of the actual shield was 3.42 T. The superconducting magnetic shield inevitably induces a high-field region near the surface of the shield, and hence the performance of the solder under high field determines the shielding ability. After testing several alloy mixtures to see which provides improved joint properties (joint resistance and therefore I/sub c/), a high-performance shield was fabricated.         SSC 40 mm cable results and 50 mm design discussions    D. Christopherson, D. Capone II, R. Hannaford, R. Remsbottom, R. Delashmit, R.J. Jayakumar, G. Snitchler, R. Scanlan and J. Royet Summary: The cable produced for the 1990 40-mm dipole program is described. The cable design parameters for the 50-mm dipole program are discussed, as well as portions of the SSC (Superconducting Super Collider) specification draft. Considerations leading to the final cable configuration and the results of preliminary trials are included. The first iteration of a strand mapping program to automate cable strand maps is introduced.         Cryostat design for the Superconducting Super Collider 50 mm aperture dipole magnet    T.H. Nicol and Y.P. Tsavalas Summary: The design of the SSC (Superconducting Super Collider) dipole magnet cryostat is described, and discussions of the thermal, structural, and dynamic considerations involved in the development of each of the major systems are included. The SSC development program has afforded the opportunity to extend the design of cryostats for superconducting magnets far beyond the state of the art achieved at the end of the Fermilab Tevatron program. Advances in new materials technology have opened up options for cryostat designers in both thermal and structural materials. Strict limits on allowable heat load have made it necessary to develop new mechanisms for structural support and thermal shielding. The end result is a cryostat design which meets the demands of the SSC and which will serve as the starting point for the development of other magnet systems.         A 40 mm bore quadrupole magnet for the SSC    C.E. Taylor, P. Barale, S. Caspi, D. Dell'Orco, D. Fritz, W.S. Gilbert, A. Lietzke, C. Peters and A. Wandesforde Summary: A 40-mm bore quadrupole magnet design, called QC, has been made for the SSC (Superconducting Super Collider) with the following parameters: a 208-T/m gradient at 6500 A and a two-layer cos 2 theta winding arrangement with 30-strand cable and one spacer wedge per coil. Structural support is provided by self-supporting interlocking collars; two types of symmetrical laminations are preassembled into collar packs for ease of assembly. A description is given of the design of a prototype quadrupole magnet for the SSC and preliminary test results on 1-m models.         Superferric correction magnets for the SSC    J. Colvin, R. Huson, W. MacKay, Y. Miao, S. Pissanetzky, R. Rocha, G. Shotzman, Y. Xiang and J. Ziegler Summary: Four models of a superferric correction quadrupole magnet were constructed for possible use in the SSC (Superconducting Super Collider); one of them was tested. The design incorporates a coil winding process. This process uses ultrasonic energy to accurately adhere a Kapton-wrapped superconducting wire in a racetrack configuration onto a substrate material 0.010 cm thick. The substrate is subsequently rolled around a frame in much the same way that a jelly roll is made. The use of iron to shape the field improves efficiency and provides a coil package preload. Design parameters and performance data are provided for the quadrupole magnet.         A numerical model for the 29-strand NET braid    E.M.J. Niessen and L.J.M. van de Klundert Summary: A discrete modeling technique is used to analyze the 29-strand NET (Next European Torus) braid in changing magnetic fields. Input for the model is the V-I relation of an individual strand and the contact resistance between touching strands. The model gives three-dimensional current patterns, V-I relations, and corresponding energy losses for the cable. The analysis shows a strong dependence of the cable properties on the direction of the field.         Modelling of dual stability in a cable-in-conduit conductor (for NET)    L. Bottura and J.V. Minervini Summary: A zero-dimensional stability model has been developed for cable-in-conduit superconductors. The model is effective in simulating the multivalued stability behavior in the vicinity of the limiting current. This has been achieved by modifying the helium heat transfer coefficient to account for inertial and frictional terms which affect the induced helium flow. The model can reproduce with remarkable accuracy the multivalued stability behavior shown in earlier measurements performed by J.W. Lue et al. (1980). A first-order approximation of the effect of the steady-state mass flow is introduced in the model, showing how an increase of the steady-state mass flow rate tends to wash away the multiple stability region as observed in the experiment.         2-D simulation of quench propagation for force-flow conductors (for NET)    L. Bottura Summary: A method for the study of the propagation of quench in the cross section of a superconducting coil wound using force-coded conductors is presented. The method is based on a detailed 2-D finite-element solution of the temperature distribution in the cross section of several adjacent conductors, taking into account the local Joule heat generation. Coolant flow through the conductor has also been modeled in an approximate way. The method has been applied to the analysis of a quench propagation experiment performed on the EU-LCT coil and to the prediction of the transversal quench propagation velocity (turn to turn or pancake to pancake) in a typical NET (Next European Torus) TF or PF conductor.         Superconducting magnet quench protection analysis and design    L. Salasoo Summary: A three-dimensional simulation of the quench thermal transient in a multicoil magnet system is described which includes circuit equations for induced secondary current transients and magnet subdivision by resistors and switching devices. Thus, the magnet designer can study the quench protection of a superconducting magnet and select the optimal protection scheme utilizing heat transfer enhancement, resistive subdivision, circuit branch switching, quench propagation heaters, coupled secondaries, and cowound stabilizers. Transient thermal profiles are available for subsequent evaluation in terms of thermal stress. An example system is modeled, and the appropriate quench protection scheme is discussed.         Performance of a 'react and wind' 12 T KfK-NET-TF subsize conductor under static and cyclic axial strain    W. Specking, A. Nyilas, A. Ulbricht, P. Komarek and R. Flukiger Summary: A forced flow Nb/sub 3/Sn subsize conductor for the 12-T Next European Torus (NET) toroidal field coils fabricated by the react-and-wind process was developed. It consists of a flat core housing the Nb/sub 3/Sn cable soldered between two stabilizing copper units which are surrounded by a stainless steel jacket. The jacket was tightly drawn onto the already reacted cable. Critical current, I/sub c/, vs. both magnetic field, B, and axial strain, in /sub a/, measurements show that this delicate procedure has not adversely affected the I/sub c/ vs. (B, in /sub a/) characteristic. At B=12 T the I/sub c/ vs. in /sub a/ curve exhibits a maximum of I/sub c/=5.25 kA at a prestrain of in /sub a/=0.36% which degrades to I/sub c/=3.93 kA at in /sub a/=0. This behavior is not influenced by 10/sup 3/ strain cycles between 0.1 and 0.36% strain. The results have demonstrated both the mechanical integrity and the predicted properties of react-and-wind conductors.         Fabrication methods of the superconducting injector cavities for the Stanford University free electron laser    A. Marziali, H.A. Schwettman, J.G. Hatmaker, M.W. Hiller, H.G. Campbell, R. Sinko, M.W. Hamilton, C.C. Coghill, R. Dunham, J.L. Light and C. Allcock Summary: Efforts to upgrade the linac driver for the Stanford University free electron laser are described. The first stage involves the construction of a 4.0-MeV, 1-mA harmonic injector system. Fabrication methods for the fundamental 1300-MHz structures are described. Similar methods are being employed in fabrication of the third harmonic structure. The structure design and the fabrication methods combine features of the original work at Stanford University and more recent work in Europe.         Residual surface losses in thin film coated RF superconducting cavities    C. Attanasio, L. Maritato and R. Vaglio Summary: Residual losses are known to be one of the main factors limiting the performance of RF superconducting cavities for particle accelerators. In particular, in thin-film sputter-coated cavities, residual terms that are strongly dependent on the RF field amplitude have been observed in the surface resistance. It is shown that RF losses at the grain boundaries can be one of the main sources of the residual surface resistivity in Nb and Nb-alloy thin-film-coated RF cavities. The effect of the film thickness on the surface impedance is also discussed.         Niobium resonator development for high-brightness ion beam acceleration    J.R. Delayen, C.L. Bohn and C.T. Roches Summary: Two niobium resonant cavities for high-brightness ion beam acceleration have been constructed and tested. The first was based on a coaxial quarter-wave geometry and was optimized for phase velocity beta /sub 0/=0.15. The cavity, which resonates at 400 MHz in the fundamental mode, operated at an average (wall-to-wall) accelerating gradient at 12.9 MV/m under continuous-wave (CW) fields. At this gradient, a cavity Q of 1.4*10/sup 8/ was measured. The second was based on a coaxial half-wave geometry and was optimized for beta /sub 0/=0.12. This cavity, which resonates at 355 MHz in the fundamental mode, operated at an average accelerating gradient of 18.0 MV/m under CW fields. This is the highest average accelerating gradient achieved to date in low-velocity structures designed for CW operation. At this gradient, a cavity of 1.2*10/sup 8/ was measured.         High electric fields in a superconducting RFQ structure    J.R. Delayen and K.W. Shepard Summary: High surface electric fields have been obtained in the first tests of a superconducting RF quadrupole device. The RF quadrupole fields were generated between niobium vanes 6.5 cm in length, with an edge radius of 2 mm and a beam aperture of 6-mm diameter. In tests at 4.2 K, the 64-MHz device operated CW at peak surface electric fields of 128 MV/m. Virtually no electron loading was observed at fields below 100 MV/m. It was possible to operate at surface fields of 210 MV/m in pulses of 1-ms duration using a 2.5-kW RF source. For the vane geometry tested, more than 10 cm/sup 2/ of surface support a field greater than 90% of the peak field. The result indicates that electric fields greater than 100 MV/cm can be obtained over an appreciable area, sufficient for some accelerator applications. It also shows that superconducting RF technology may provide an extended range of options for RF quadrupole design.         Activities on superconducting accelerating cavities at LNF    R. Boni, D. Di Gioacchino, A. Gallo, U. Gambardella, M. Minestrini, F. Tazzioli and C. Vaccarezza Summary: In the framework of the Linear Superconducting Accelerator (LISA) project, a facility was setup for testing 500-MHz single-cell cavities in a vertical cryostat. To investigate the effect of different chemical treatments, bulk Nb single cells welded from the inside were constructed in cooperation with national manufacturers. Preliminary results of the RF measurements in a cryogenic environment are reported and discussed.         Reducing field emission in superconducting RF cavities for the next generation of particle accelerators    Q.S. Shu, W. Hartung, A. Leibovich, J. Kirchgessner, D. Moffat, R. Noer, H. Padamsee, D. Rubin and J. Sears Summary: Heat treatment up to 1500 degrees C in an ultrahigh-vacuum furnace, along with processing of cavities and temperature mapping was used to suppress field emission and analyze emitter properties. In 27 tests of one-cell 1500-MHz fired accelerating cavities, on the average the accelerating field, E/sub acc/, increased to 24 MV/m (H/sub pk/=1250 Oe) from 13 MV/m with chemical treatment alone; the highest E/sub acc/ reached was 30.5 MV/m. Emitter properties, efficiency of He processing, and results of the exposure of well-processed RF surfaces to various media are also discussed.         Performance of the eight superconducting quadrupole magnets for the TRISTAN low-beta insertions    K. Tsuchiya, K. Egawa, K. Endo, Y. Morita, N. Ohuchi and K. Asano Summary: The low-beta insertion quadrupoles are iron-free superconducting magnets with an inner coil diameter of 140 mm, an effective length of 1.14 m, and a nominal gradient of 70 T/m. The coils, which are of the cos 2 Theta type, are made from four layers of 27-strand NbTi Rutherford-type cable with Kapton insulation and are firmly clamped with 316LN stainless steel collars. Following the development of prototype magnets, eight magnets have been produced and were thoroughly tested and measured prior to installation in the TRISTAN main ring. A brief description of the design and manufacturing technique and the results of tests and measurements are presented.         Development of an ASTROMAG test coil with aluminum stabilized superconductor    Y. Makida, Y. Doi, T. Haruyama, H. Inoue, N. Kimura, S. Saito, K. Tanaka, A. Yamamoto and H. Yamaoka Summary: An ASTROMAG test coil with aluminum stabilized superconductor is being developed. The pure aluminum stabilizer will improve stability of the superconducting coil within the limited weight. A test coil that is approximately full size compared to the ASTROMAG main coil was designed. A description is given of the design study and progress in test coil development.         The quench analysis of a 6 T SC wiggler for Adone at Frascati    M. Barone, A. Cattoni, R. Marabotto, G. Masullo, R. Puzone and C. Sanelli Summary: A single-pole, 6-T, superconducting wiggler with two racetrack NbTi superconducting coils separated by a central plate and kept together by two iron yokes has been designed and built. The superconducting magnet and two low-field compensating warm poles will be installed in the straight section no.10 of the e/sup +/,e/sup -/ storage ring Adone, to be used as a wavelength shifter to produce a hard X-ray flux of 2.4*10/sup 12/ photons/s/mrad in 0.1% bandwidth at a critical energy of 9 keV, six times higher than the one produced by the accelerator bending magnets. An analysis is presented of a typical quench.         The superconducting beam transport system at the NSCL    A.F. Zeller, J.C. DeKamp, C.T. Magsig and J.A. Nolen Summary: The beam transport system at the National Superconducting Cyclotron Lab (NSCL) consists of 22 cryostats containing superconducting quadrupole doublets or triplets, and 9 superconducting dipoles. The quads achieve gradients of up to 35 T/m in the 10-cm-diameter warm bore. Operating at a maximum current of 20 A allows the helium consumption rate to be kept to less than 0.3 L/h. The dipoles produce fields in the 5-cm gap of over 1.9 T at a current of 100 A, and the two types produce bends of either +or-16 degrees or 22.5 degrees at 1.75 T for the 1.6-GeV/c heavy ion beams produced by the K1200 superconducting cyclotron. One year's operations experience demonstrates their efficiency and reliability.         Zeus thin solenoid: test results analysis    A. Bonito Oliva, O. Dormicchi, M. Losasso and Q. Lin Summary: The thin solenoid for the Zeus detector has been installed and tested in HERA (Hadron Electron Ring Accelerator) at DESY. The coil reached the design magnetic field (1.8 T in the center) without training. During the test some measurements were made in order to investigate the cooling system and the quench-back behavior. No spontaneous quenches occurred. Several induced fast discharges showed the evidence of a quench-back effect, and the quench-back starting time was less than 1 s. The cylinder temperature measurements during the coil discharge perfectly agree with adiabatic calculations. The indirect cooling efficiency was verified for the two-layer winding. The tests performed showed that the magnet can operate safely at the nominal field.         The compensating magnet for the Zeus detector    O. Dormicchi, R. Penco, S. Parodi, P. Valente, A. Bonito Oliva, G. Gaggero, M. Losasso, G. Masullo and Q. Lin Summary: A bath-cooled superconducting solenoid with a 280-nm-diameter warm bore, a coil length of 1200 mm, and a central field of 5 T at the rated current of 950 A has been built. It will operate as the compensating coil inside the Zeus detector at HERA (the Hadron Electron Ring Accelerator) at Desy. The coil is shielded by a 3.5-ton low carbon steel cold yoke, and the cold helium chamber was designed to withstand a maximum pressure of 20 bar. The main results obtained during the cool down and energization are reported.         Construction of a large superconducting spectrometer magnet    T. Shintomi, K. Aoki, Y. Doi, Y. Makida, O. Hashimoto, T. Kitami, T. Miyaji, T. Nagae and M. Sekimoto Summary: A sector-type superconducting spectrometer magnet for nuclear physics experiments has been constructed. The central magnetic field is 3 T with a magnet gap of 50 cm and a stored energy estimated to be 11.2 MJ. Three-dimensional magnetic field calculations and a stress analysis have been performed to design the coil and supporting structures. The magnet has a flexible helium transfer line to measure angular distributions at nuclear physics experiments. To simplify the transfer line, a small-size G-M refrigerator, which is installed on a service port of the helium vessel, is used for thermal insulation at 80 K and 20 K in combination with a medium-size refrigerator for cooling the magnet at 4 K. The heat leak at 4 K is estimated to be 3 W at 4 K. The maximum operation current of 500 A is selected by considering the maximum temperature of the coil at quench. In preliminary cooling tests, the magnet has been cooled within 52 h as expected.         New measurements of magnetic field decay in 1 meter SSC-type dipoles    W.S. Gilbert, R.F. Althaus, P.J. Barale, R.W. Benjegerdes, M.A. Green, M.I. Green and R.M. Scanlan Summary: Previous studies of magnetic field decay in model SSC (Superconducting Super Collider) dipoles due to changes in magnetization currents caused by flux creep have used the assumed SSC injection energy of 1 TeV, or an 0.33-T central dipole field, and an excitation to the storage field of 6.6 T. More recently, it has been decided to inject at 2 TeV, or 0.66 T and so more recent tests have been carried out at the new injection field, or at both the new and old fields. Additionally, the effects of temperature changes and excitation cycles on the field decay have been studied. The roughly log linear decay of magnetization current multipole fields has been demonstrated in several new dipoles. A suggested mechanism of thermally induced activation in the additional 0.5-K range has been effectively countered by temperature measurements that show temperature fluctuation ten to thirty times lower, over a 90-min time period.         Design study of a phi 19.5*36 m superconducting solenoid (for supercollider Multi-TeV detector)    P. Bruni, S. Ceresara, Y. Li, Q. Lin, B. Musso and A. Zichichi Summary: A large detector is being developed to measure teraelectronvolt massive objects decaying into muon pairs in a high luminosity (10/sup 33/-10/sup 34/ cm/sup -2/ s/sup -1/) pp collider. The mass resolution should be Delta M/M=1%. The momentum measurement of charged particles is achieved with the help of a very large superconducting solenoid which is surrounded by an octagonal iron yoke of 34770 tons. The magnetic field design, the design of the restraining cylinder, the thermosiphon cooling system, and the mechanical design are discussed.         Quench propagation in the SSC dipole magnets    G. Lopez and G. Snitchler Summary: The effects of quench propagation are modeled in 40-mm- and 50-mm-diameter collider dipole magnet designs. A comparative study of the cold diode (passive) and quench heater (active) protection schemes is presented. The SSCQ modeling program accurately simulates the axial quench velocity and uses phenomenological time delays for turn-to-turn transverse propagation. The axial quench velocity is field dependent and, consequently, each conductor's quench profile is tracked separately. No symmetry constraints are employed, and the distribution of the temperatures along the conductor differs from the adiabatic approximation. A single magnet has a wide margin of self-protection, which suggests that passive protection schemes must be considered.         Strain energy minimization in SSC magnet winding    J.M. Cook Summary: Differential geometry provides a natural family of coordinate systems, the Frenet frame, in which to specify the geometric properties of a magnet winding. By a modification of the Euler-Bernoulli thin rod model, the strain energy is defined with respect to this frame. Then, it is minimized by a direct method from the calculus of variations. The mathematics, its implementation in a computer program, and some analysis of a Superconducting Super Collider (SSC) dipole by the program are described.         Winding mandrel design for the wide cable SSC dipole    G.H. Morgan, A. Greene, G. Jochen and A. Morgillo Summary: The 50-mm coil (i.d.) Superconducting Super Collider (SSC) dipole magnets use wider cables to give a greater operational margin between the quench field and the operating field. The cable used for the inner coil has 30 strands of the same size (0.808 mm) instead of 23, the outer has 36 strands of the same size (0.648 mm) instead of 30, and the cable widths are increased in proportion. Although the inner diameter of the coil has been increased from 40 mm, the coil ends are noticeably harder to wind. The authors describe the computational and experimental effort to design winding mandrels or center posts for the constant-perimeter ends.         Accelerator magnet designs using superconducting magnetic shields    B.C. Brown Summary: The possibility of a superconducting shield for accelerator dipole and quadrupole magnets is explored. It is found that the decentering instability associated with iron shields is avoided by the strong diamagnetic shield. In addition, the shield can be much thinner, occupying less radial space in the cryostat. By avoiding the weight and decentering forces of the iron shield, one can reoptimize the cryostat design and substantially reduce the mass which must be cooled to helium temperatures. Promising applications in which these advantages are important are p-p collider interaction region quadrupoles, corrector dipoles for collider detectors, and high-field accelerator dipoles.         Measurements of passive correction of magnetization higher multipoles in one meter long dipoles (for SSC)    M.A. Green, R.F. Althaus, P.J. Barale, R.W. Benjegerdes, W.S. Gilbert, M.I. Green, R.M. Scanlan and C.E. Taylor Summary: The use of a passive superconductor to correct the magnetization sextupole and decapole in Superconducting Super Collider (SSC) dipoles appears to be promising. The results of a series of experiments on passive superconductor correctors in 1-m-long dipole magnets are presented. Reduction of the magnetization sextupole by a factor of 5-10 has been achieved using the passive superconductor correctors. The magnetization decapole was also reduced. The passive superconductor correctors reduced the sextupole temperature sensitivity by an order of magnitude. Flux creep decay was partially compensated for by the correctors.         A Nb/sub 3/Sn high field dipole (for SSC)    R. McClusky, K.E. Robins and W.B. Sampson Summary: A dipole magnet approximately 1-m long with an 8-cm bore has been fabricated from cable made from Nb/sub 3/Sn multifilamentary strands. The coil consists of four layers of conductor wound in pairs to eliminate internal joints. Each set of layers is separately constrained with Kevlar-epoxy bands, and the complete assembly is clamped in a split laminated iron yoke. The inner coil pairs were wound before heat treating, whereas the outer coils were formed for prereacted cable using conventional insulation. A NbTi version of the magnet was fabricated using Superconducting Super Collider (SSC) conductor to test the construction techniques. This magnet reached a maximum central field of 7.6 T, at 4.4 K, which is very close to the limit estimated from conductor measurements. The Nb/sub 3/Sn magnet, however, only reached a maximum field at 8.1 T, which is considerably short of the field expected from measurements on the inner cable.         Development of an experimental 10 T Nb/sub 3/Sn dipole magnet for the CERN LHC    H.H.J. ten Kate, A. den Ouden, D. ter Avest, S. Wessel, R. Dubbeldam, W. van Emden, C. Daum, M. Bona and R. Perin Summary: An experimental 1-m long twill aperture dipole magnet developed using a high-current Nb/sub 3/Sn conductor in order to attain a magnetic field well beyond 10 T at 4.2 K is described. The emphasis in this Nb/sub 3/Sn project is on the highest possible field within the known Large Hadron Collider (LHC) twin-aperture configuration. A design target of 11.5 T was chosen.         Optimizing the conductor dimensions for a 10-13 T superconducting dipole magnet (for accelerators)    D. ter Avest, H.H.J. ten Kate and L.J.M. van de Klundert Summary: A method to obtain systematic solutions for the conductor dimensions and their layout is described. From these solutions a selection can be made based on a number of practical requirements. The inclusion of a measured J/sub max/(B) relation of the superconductor in order to make the design practical has a large effect on the geometry. A dipole magnet with cables of equal width is not necessarily the best solution; it is often better to have a broader inner-layer cable. The volume of superconductor appeared to vary only within a few percent in the systematic solutions and is therefore not a relevant criterion. In the case of a 13-T dipole magnet and using the J/sub max/(B) relation described, more than two layers of conductors must be used in order to keep the design within practical limits. It appears to be difficult to obtain a convenient solution for a 13-T magnet, although the number of geometrical variants is very high.         Design study of a superconducting dipole model magnet for the Large Hadron Collider    H. Hirabayashi, A. Yamamoto, S. Kawabata, G. Brianti, D. Leroy and R. Perin Summary: A design study of a high-field superconducting dipole magnet for the LHC (Large Hadron Collider) project has been carried out in cooperation between CERN and KEK. The objective is to develop a 1-m twin-aperture dipole model magnet based on double shell coil design with a fully symmetric split collaring structure. Development of superconducting cable with high keystone angle is a key technology to realize this magnet. The progress made in the design study and the development of the 1-m dipole model magnet are described.         Measurements on electrical contact resistance of internal coil connections for LHC high field dipole magnets    F. Zerobin, F. Baumann, H. Kofler and F. Ramsauer Summary: Measurements are presented of electrical contacts of internal coil connections in high-field dipole magnets for the proposed LHC (Large Hadron Collider) machine at CERN. A test station was built to test samples up to 40 kA in an external magnetic field of up to 6 T at 4.2 K. The experimental setup, the samples, and the results are described and discussed.         Collider dipole magnet field angle measurement    G.W. Albert, S.V. Pidcoe, S.D. Peck and R.E. Bailey Summary: Methods and devices for measuring the prototype Superconducting Super Collider (SSC) dipole magnetic field angle with respect to a vertical reference are discussed. An internal research and development project was conducted to develop a low-cost device for production measurement of the SSC dipole field verticality. The system employs Hall probes, a level sensor, and precision electronics interfaced to a personal computer to perform this critical measurement at discrete points along the magnet beam axis. Specification, component selection, mechanical and electrical design, calibration, and test results are presented.         Mechanical and electronic analysis of 50 millimeter designs for the SSC dipole    J. Jayakumar, K. Leung, F. Nobrega, D. Orrell, P. Sanger, G. Snitchler, G. Spigo, J. Turner, C. Goodzeit, R. Gupta, S. Kahn, G. Morgan, E. Willen, J. Kerby, J. Strait and R. Schermer Summary: Several designs for the Superconducting Super Collider dipole magnet have been analyzed. The mechanical and electromagnetic features of each design is discussed. Electromagnetic and mechanical analyses were performed using hand, computer programs, and finite-element techniques to evaluate the design. It was found that a substantial increment of stresses in the end skin occurs if the end yoke is not welded to the skin. The magnitude of friction coefficients has a negligible effect on the skin stress. The margins of safety are 1.17 for a design using an end skin with a welded end yoke and 0.51 for a design using end skin lap-jointed to the end yoke.         Control of a superconducting coil by a MOSFET power converter operating at near liquid nitrogen temperature    T. Ise and Y. Murakami Summary: The on-resistance of a power MOSFET has a minimum value at around 80 K. This characteristic was utilized in order to operate a power converter circuit using power MOSFETs in a cryostat with a superconducting coil. As a result, it was confirmed that power losses of the chopper circuit and the size of the current leads can be greatly reduced. The power loss of the circuit was half of that at room temperature, and the loss can be reduced further by using diodes with lower on-voltages at low temperatures. The size of the current leads was reduced by using the chopper circuit as a DC transformer.         Resolutions to difficulties experienced in SSC cable fabrication during the initial scale-up period    R. Hannaford, D. Christopherson, B. Remsbottom and M. Boivin Summary: A prototype high-speed cable machine for the Superconducting Super Collider (SSC) has produced the majority of the cable needed for the SSC Dipole Program. However, several cabling difficulties were experienced that were not seen previously. These difficulties were due to new techniques and equipment relating to the high-speed production of cable meeting SSC specifications. These difficulties included mandrel alignment, Turk's-head roller alignment, and Turk's-head drive equipment. The solution to these problems is discussed. By modifying the Turk's head, it is possible to manufacture SSC cable to the current specifications without defects.         Nb/sub 3/Sn multifilamentary superconductors: an updated comparison of different manufacturing routes    M. Thoner, H. Krauth, A. Szulczyk, K. Heine and M. Kemper Summary: Bronze route Nb/sub 3/Sn conductors can be designed to exhibit the best performance in terms of uniformity as measured by the n value and as needed for persistent mode operation. When designed for low magnetization and low hysteresis losses bronze route conductors exhibit the best combination of critical current density, effective filament diameter, and hysteresis losses. The filament coupling losses can be kept small due to the high resistivity of the bronze and the good twistability of the wires. It is concluded that the fabrication technology and reliability of bronze route conductors have reached high standards which cannot readily be achieved with other fabrication technologies.         High strength Nb/sub 3/Sn conductors for high magnetic field applications    E. Gregory, L.R. Motowidlo, G.M. Ozeryansky and L.T. Summers Summary: A relatively-high-conductivity copper-based material which retains its high strength after reaction heat treatment has been used to replace some of the copper stabilizer, both on the outside of the conductor and between the filaments. It is shown that a dispersion hardened copper alloy, C15715, containing 0.7 vol.% Al/sub 2/O/sub 3/, can be incorporated into a tabular tin source (TTS) material in two different locations, without significant fabrication problems. The alloy could also be applied to the other processes for producing the Nb/sub 3/Sn, including the bronze process. When the alloy is located between the filaments, it should decrease the sausaging that may occur in the certain designs. When used to replace the high purity copper stabilizer on the outside of the TTS and conventional internal tin materials, very significant increases in the overall strength of the conductor result.         Influence of production parameters on the superconducting properties of NbTi and Nb/sub 3/Sn wires    L.J.M. van de Klundert Summary: The commercial specification of superconducting NbTi and Nb/sub 3/Sn composite wires is normally given by parameters such as the critical current (which is dependent on conductivity, temperature, and magnetic field), an empirically deduced parameter for which the effective resistivity is about 10/sup -14/ Omega m, wire and filament diameter, and twist length. To some extent their values cannot be chosen independently, nor do they guarantee proper operation of the system in all aspects. It is argued that for Nb/sub 3/Sn composite, depending on the production process, an extra set of parameters describing the stress sensitivity seems to be needed to specify the quality of the composite.         A model for the prediction of Nb/sub 3/Sn critical current as a function of field, temperature, strain, and radiation damage    L.T. Summers, M.W. Guinan, J.R. Miller and P.A. Hahn Summary: An empirical model is presented that predicts the critical current density (J/sub c/) of Nb/sub 3/Sn wires under the combined effects of temperature, strain, and radiation damage. The model, based on previous work of D.P. Hampshire et al. (1985) and J. W. Ekin (1980), predicts J/sub c/ with a reasonable degree of accuracy. The model can be used with a limited number of input parameters. eliminating the need for detailed characterization, particularly the difficult tasks of measuring critical current as a function of temperature and radiation damage.         Nb tube processed Nb/sub 3/Al multifilamentary superconductors    T. Takeuchi, M. Kosuge, Y. Iijima, A. Hasegawa, T. Kiyoshi and K. Inoue Summary: In addition to microstructural studies, various characteristics of Nb tube processed Nb/sub 3/Al multifilamentary (MF) conductors needed in designing superconducting magnets are described. With decreasing Al core diameters of the Nb/Al composite, the formation rate of the A15 phase increased, and its lattice parameter decreased conversely. This was accompanied by an increase in T/sub c/ and H/sub c2/ (4.2 K), suggesting that the small diffusion spacing between Nb and Al facilitates the formation of the metastable A15 phase with stoichiometric composition. On the other hand, both the value of V-I curve and its field dependence decreased with decreasing Al core diameter below 50 nm, which suggests the sausaging of Al filaments in the heavily cold-worked sample. The reversible bending strain range was up to at least 1.4%, indicating the applicability of the react-and-wind method. The degradation in the J/sub c/ (4.2 K, 12 T) of the solenoid with 1.8% winding strain was about 20%. A decrease in temperature from 4.2 to 1.8 K caused an increase of H/sub c2/ by 2.5 T.         Production of superconducting Nb/sub 3/Sn wire using Nb or Nb(Ti) and Sn(Ga) solid solution powders    C.L.H. Thieme and S. Foner Summary: Superconducting Nb/sub 3/Sn wire was produced by a powder metallurgy method using Nb or Nb-2.9 at.% Ti powder in combination with Sn-x at.% Ga powders (x=3, 4.2, 6.2, and 9.0). Ga additions to the Sn caused considerable solid solution hardening, which improved its workability. It made the Nb-Sn(Ga) powder combination convenient for swaging and extensive wire drawing. Anneals at 950 degrees C produced wires with an overall J/sub c/ of 10/sup 4/ A/cm/sup 2/ at 21.9 T for wires with both Ti in the Nb and 6.2 at.% Ga in the Sn. Comparison of this wire with best Nb(Ti)-Cu-internal Sn(Ti) shows a higher J/sub c/ per A15 area, especially in fields of 22 T and above.         Monitoring and controlling TORE SUPRA toroidal field system status after a year of operating experience at nominal current    J.L. Duchateau, D. Bessette, D. Ciazynski, J. Pierre, E. Rouanet, P. Riband and B. Turck Summary: The superconducting toroidal field system of TORE SUPRA stands out as one of the major aspects of this Tokamak. The system was tested in November 1989 at up to 1455 A (4.5 T on the plasma axis), followed by operation for a year. During this period, special attention was paid to system monitoring. Five detection systems acting independently ensure the reliability of the safety system in case of resistive transition. Classical differential voltage detection plays an important part. In addition, experience has been gained on the thermal behavior of a coil in case of local heating, providing a practical basis for overpressure and temperature increase detection. The quench of coil BT4 due to nuclear radiation in December 1989, following a severe plasma disruption at 1.9 MA, demonstrates the ability of the safety system to efficiently detect the transition and to limit the energy dissipated inside the coil through a low voltage oriented discharge.         The current capacity tests of the Tokamak T-15 Nb/sub 3/Sn toroidal coil assembly    V.A. Alkhimovich, I.O. Anashkin, N.N. Britousov, A.N. Vertiporokh, A.N. Zuravlev, D.P. Ivanov, D.R. Pogonischev, I.A. Posadskiy, Y.G. Radin, B.A. Stavisskiy, V.S. Strelkov, P.P. Khvostenko, N.A. Chernoplekov, V.A. Glukhikh, S.A. Gulevich, V.G. Dubasov, M.V. Zhelamskiy, N.A. Monoszon, G.V. Trokhachev, O.G. Filatov and G.F. Churakov Summary: The Nb/sub 3/Sn magnet toroidal field coil assembly of Tokamak T-15 has shown its workability up to the rated magnetic field (3.5 T at the axis and 6.6 T at the coils). The dependence of the quench current on winding temperature was obtained. Its extrapolation shows that operation at 4.5 T will be possible at a temperature of 4.5 K. The coil which limits the total current of the coil assembly was identified. Poloidal field changes produced by plasma current disruptions with a field change rate of up to 15 T/s did not disturb the coil assembly operation.         Experimental results of the Nb/sub 3/Sn demo poloidal coil (DPC-EX)    T. Ando, K. Okuno, H. Nakajima, K. Yoshida, T. Hiyama, H. Tsuji, Y. Takahashi, M. Nishi, E. Tada, K. Koizumi, T. Kato, M. Sugimoto, T. Isono, K. Kawano, M. Konno, J. Yoshida, H. Ishida, E. Kawagoe, Y. Kamiyauchi, Y. Matsuzaki, H. Shirakata and S. Shimamoto Summary: In order to demonstrate the applicability of a Nb/sub 3/Sn conductor to pulsed poloidal coils for Tokamak fusion machines, the Nb/sub 3/Sn Demo Poloidal Coil (DPC-EX) has been fabricated and tested. DPC-EX, whose inner diameter is 1 m, consists of two double pancakes made by a react-and-wind technique. The coil has a flat cable-in-conduit conductor cooled by forced-flow helium. DPC-EX has been set up in the Demo Poloidal Coil Test Facility (DPCF). In the operation of the coils in series, DPC-EX has been ramped up to 17 kA in 1 s. The magnetic field at this point was 6.7 T, and pulsed operation at 6.7 T/s was thus demonstrated. An average current density of 37.2 A/mm/sup 2/ in the winding was achieved in this operation, and the AC loss of the coil was confirmed to be quite small.         Nb/sub 3/Sn conductor development programme for superconducting coils for the European Fusion Programme    N. Mitchell, L. Bottura, P. Bruzzone, F. Fardi, J. Minervini, M. Perrella, R. Poehlchen, M. Ricci and E. Salpietro Summary: The major part of the program involves the industrial fabrication of long lengths of full-size conductors and the manufacturing of test coils that will be thoroughly tested in a single test facility (TOSKA, at KfK Karlsruhe, Germany). A total of 3.5 km of 40-kA conductor is required to form circular model coils with an inner bore of 2 m and a peak field of over 13.5 T. Short (5-m) lengths of full-size 40-kA conductors have been manufactured. The present results on the industrial fabrication of 12-T, 40-kA cable-in-conduit conductors for the Next European Torus (NET) indicate that the machine design criteria can be satisfied and that the conductor is suitable for large-scale industrial fabrication.         24 Tesla superconducting toroidal field magnet concept for a commercial Tokamak reactor    J. Schwartz, L. Bromberg, D.R. Cohn and J.E.C. Williams Summary: A 24-T superconducting toroidal field magnet concept for a commercial fusion power reactor is discussed, and a magnet development path is outlined. Superconducting and structural materials options are discussed within the framework of a 20-yr development time. Nb/sub 3/Sn may be capable of operating at up to 18-20 T. For B>20 T, Nb/sub 3/Al, Nb/sub 3/(Al,Ge) or ceramic high-T/sub c/ superconductors are required. Enhanced strength and stiffness and reduced conductor bending stress are obtained with carbon fiber reinforced steel (Incoloy 908) as the primary structural material. Composite behavior is analyzed using a two-dimensional orthotropic failure criterion. The size of the magnet is minimized subject to electromagnetic, mechanical, and practical constraints.         Quench propagation in a cable-in-conduit force-cooled superconductor-preliminary results    J.W. Lue, S.W. Schwenterly, L. Dresner and M.S. Lubell Summary: A preliminary test was performed to measure quench propagation in a cable-in-conduit superconductor. Although the data are not extensive, the behavior of the sample was similar to that reported by T. Ando et al. (1989) for tests performed at the same current densities (though at 7-T field). The propagation increased with time, a phenomenon that can only be explained by thermal hydraulics of the coolant. The maximum propagation velocity was about 5 m/s at a current density of 100 A/mm/sup 2/. The propagation velocity (tens of meters per second) predicted by others was not observed. Based on the measured initial normal zone hot helium expansion velocity, the condition for use of the finish time formula of L. Dresner was not met in either the present experiment or in Ando's experiment. It is not clear whether the observed slightly higher power dependence of normal zone velocity on elapsed time is due to changes in helium expansion velocity or is a result of THQ (thermal hydraulic quenchback). Further studies, both analytical and experimental, are needed before the existence of THQ can be verified.         Normal-zone propagation velocity in superconducting wires having a CuNi matrix    A. Ishiyama, Y. Sato and M. Tsuda Summary: The thermal behavior and the electromagnetic behavior of superconducting wires during quench are apparently different from those of conventional copper-stabilized composites. To investigate these properties, the authors consider the effects of the temperature gradient in a radial direction of the wire cross-section and the redistribution of currents in the normal-zone wavefront. They measured longitudinal normal-zone propagation velocities in NbTi/CuNi composite wires (strands) with different cooling characteristics and compared the measurement results with analytical results obtained by means of the three-dimensional finite-element method (3-D FEM), taking into account the redistribution of currents and the influence of the transverse electrical conductance on the current sharing in a composite. The analytical and experimental results agree well. On the basis of these comparisons, the mechanism of normal-zone propagation in superconducting wires with a CuNi matrix is discussed.         Quench protection of superconducting transformers    M. Iwakuma, K. Funaki, M. Takeo and K. Yamafuji Summary: Protection of superconducting transformers from the quench caused by excess fault current was studied theoretically with the aid of a simple equivalent circuit model which was composed of leakage inductance and resistances of the conductor. The authors distinguished the resistance in the flux-flow state from that in the normal state, and basic parameters of the transformer, such as sizes, leakage inductance, and conductor length, were determined as functions of one-turn voltage. The quench process after the short-circuit was numerically analyzed by this circuit equation with the aid of the heat-balance equation. The maximum temperature rise of the conductor until interruption of the power line was found to increase monotonically with the one-turn voltage, but the minimum is around several percent of the copper ratio in the conductor. To suppress the temperature rise, therefore, the one-turn voltage should be limited to smaller values than in conventional transformers, even if the copper ratio is optimized for the rated capacity and voltage.         Quench simulation of 4.7 Tesla superconducting magnet for magnetic resonance spectroscopy    S. Fujimura and M. Morita Summary: A description is given of a simulation method that calculates the time dependencies of current and voltage for multiple coils under the condition that the coils were quenched. This method is used to calculate the current changes and temperature rise in a 4.7-T superconducting small bore magnet. It is found that the temperature rise is less than 200 K in superconducting shim coils and 125 K in main coils. Consequently, coils can be protected without protection resistance.         Heater-induced quenches in a model field winding for the 70 MW class superconducting generator    H. Yoshimura, A. Ueda, M. Morita, S. Maeda, M. Nagao, K. Shimohata, Y. Matsuo, Y. Nagata, T. Yamada and M. Tanaka Summary: Quench studies were performed using a model field winding for the 70-MW-class superconducting generator to investigate the minimum quench energy, the longitudinal and turn-to-turn quench propagation velocities, and the temperature rise of the hot spot. The model field winding is a racetrack coil with 88 turns which was wound in a slot of the support structure and compressed by a flange. The 15-strand cable was selected as a conductor to reduce the AC losses that will be generated at the system fault. A ceramic chip heater was glued on the surface of the racetrack coil to initiate quenches. Two pairs of voltage taps were used to determine the quench propagation velocities. A Cu+0.15% Fe-Chromel thermocouple was soldered near the ceramic chip heater to measure the hot spot temperature. The data obtained in these experiments will be used to design the quench protection system for the field windings of the 70-MW-class superconducting generator.         Quench propagation analysis in adiabatic superconducting windings    A. Ishiyama, H. Matsumura, W. Takita and Y. Iwasa Summary: The basic postulate of the quench simulation code, developed to analyze normal-zone propagation in adiabatic magnets, is that the code's computation may be greatly simplified without sacrifice in accuracy by aggregating all thermal properties of the winding affecting normal-zone propagation into a single parameter of the transverse quench velocity. In order to verify this postulate, a finite-element method (FEM) analysis was applied to solve the temporal and spatial evolution of temperature within a section of an adiabatic magnet winding. Agreement between the FEM results and those of the simulation code is excellent. The FEM is also an important tool for refining the code and developing a more accurate scaling law for the code. A test case is presented in which the refined code is used to analyze an adiabatic magnetic previously studied experimentally.         PQUENCH-A 3-D quench propagation code using a logical coordinate system    M. Oshima, R.J. Thome, W.R. Mann and R.D. Pillsbury Jr. Summary: A computer program was developed to model the effects of normal region propagation in the longitudinal direction (along the conductor) and in the two transverse directions in a superconducting coil in a multicoil system. A simulation of 3-D quench propagation in real space was done using a logical coordinate system in which each magnet is transformed into a single long conductor which is divided into finite-length elements. Since an element can be associated with geometry-related information such as the element length, the local magnetic field influence coefficients, and the relationship to adjacent elements in 3-D, the quench propagation in any type of 3-D configuration can be simplified to a 1-D problem. As the growth of the normal region is determined, the transient current decay is calculated based on increases in conductor temperature and resistance. This calculation can be done for multiple, inductively coupled systems through the use of a circuit analysis subroutine. The code logic is described, and results are given for calculated versus measured quench times in a single-coil system.         Numerical modeling of normal zone propagation and heat transfer in a superconducting composite tape    M.K. Chyu and C.E. Oberly Summary: A numerical model has been developed to analyze the dynamic evolution of the normal zone in a composite tape made of YBCO superconductor with silver cladding as stabilizer. The model solves the conjugate two-dimensional, transient heat equation coupled with current sharing between a clearly segregated superconductor and stabilizer. Heat removal in the transverse direction is characterized by a heat conductance imposed on the stabilizer's outer surface. The computational results indicate that the present tape configuration is much more stable against a pulse disturbance than its counterparts predicted from the conventional one-dimensional theory with volumetrically averaged properties. Conventional one-dimensional analyses for magnet stability have been demonstrated to be too conservative in many aspects. The detailed distribution of heat generation in the composite depends strongly on both the transverse heat transfer and the magnitude of operating current. Ohmic heating in the stabilizer can be very significant, especially for the cases with low heat conductance and/or a large operating current.         Device for investigation of mechanical stresses in superconducting windings    V.R. Karasik, A.A. Konjukhov, V.A. Malginov and M.V. Sidorov Summary: A description is given of a device for the investigation of the influence of the mechanical stresses on training and critical parameters of superconducting windings placed in an external magnetic field of up to 4.5 T. The test coil diameter is about 650 mm. The maximum value of the effective tension is more than 1000 MPa. The results of a preliminary test on the thin coil (a/sub 1/=325 mm, a/sub 2/=328 mm, 2b=18 mm) with a stainless steel bobbin and bandage under tangential tension are presented.         Pressure drop measurements on cable-in-conduit conductors of various geometries    M.A. Daugherty and S.W. Van Sciver Summary: Measurements are made of the pressure drop on various cable-in-conduit conductors with different void fractions, number of strands, and flow areas. To carry out these measurements, supercritical helium is circulated through a loop containing several conductor sections instrumented with cold pressure transducers. A cold centrifugal pump is used to force the helium through the loop at flow rates of up to several grams per second. The modular design of the flow loop allows for relatively easy insertion of different test sections. Pressure drops, measured at different temperatures and mass flow rates, are correlated using classical friction factor analysis. Some variation in friction factor appears to result from temperature or helium property changes.         Flow visualization of coolant in cable-in-conduit conductor    T. Amano, A. Ohara and T. Yamada Summary: Flow visualization to observe the flow behavior of a coolant in a cable-in-conduit conductor was performed by nuclear magnetic resonance (NMR) imaging. A dummy conductor in which many vinyl strings were inserted into an acrylic tube was used for visualization. Regions of both high and very low flow velocity, in comparison with the average velocity, existed in a cross section of the conductor. This fact shows that the flow behavior of the coolant in the cable-in-conduit conductor is not homogeneous but heterogeneous. Thus it is not possible to directly apply a numerical code based on homogeneous flow behavior to stability analysis of the cable-in-conduit conductor.         Numerical analysis of length effects on stability and quench behavior in CICC    J. Basecq Summary: One-dimensional numerical models of cable-in-conduit conductors (CICCs) have been developed. They have been extensively used to analyze cables proposed for the Next European Torus (NET) outer poloidal field coils. Some peculiar features of the thermodynamic behavior of CICC which were observed in that study are presented. In particular, the effect of the initial disturbance length on stability margin, quench propagation velocity, maximum pressure, and temperature is considered. It is found that going to smaller disturbance lengths can lead to significantly improved stability margins and potentially troublesome quench behavior.         Numerical and analytical solutions for the dynamic stability of edge cooled superconducting tapes using two dimensional variational principles    J. Schwartz, J.P. Freidberg and J.E.C. Williams Summary: The dynamic stability of an edge cooled superconducting tape is a nonlinear, 3-D magnetothermal problem. In this analysis, a 2-D linearized version is solved using variational principles. To model the physical behavior of the conductor accurately, trial functions are carefully chosen subject to the exact boundary conditions and a numerical solution is obtained. This solution is compared to a recently obtained analytic solution and the 1-D solution obtained by H.R. Hart Jr. (1968). The 2-D analysis indicates that the finite thermal diffusion in the superconductor can play a significant role for w/sub o//d/sub SC/<100, where w/sub o/ is the half width of the tape and d/sub SC/ is the thickness of the superconductor.         Instability of persistent current switch    H. Maeda, M. Urata, Y. Oda, M. Kageyama and S. Kabashima Summary: The instability for a persistent current switch (PCS) wound bifilarly by a CuNi matrix conductor was studied experimentally and by numerical calculations. The temperature rise due to self-field AC loss during the ramping up of the current causes degradations. The quench current gradually decreases to the adiabatic value, if the current sweep rate is progressively increased. Current transfer from the current terminal to the winding limits the current capacity for the PCS wound by a thick conductor, such as 0.9 mm in diameter. A short ramp pulse causes premature quenches at extremely low currents, which may be due to heat concentration of the self-field AC loss in the conductor outer shell.         Instability of superconducting racetrack magnets    K. Ikizawa, N. Takasu, Y. Murayama, K. Seo, S. Nishijima, K. Katagiri and T. Okada Summary: The training and degradation behavior of superconducting racetrack-shaped magnets were studied for use in a high-performance superconducting wiggler. Several small magnets that were fabricated with NbTi multifilamentary superconductor and impregnated with epoxy resin were tested by changing the winding tension, aspect ratio of the magnets, and copper ratio of the superconductor. The acoustic emission signals were monitored during the tests. The correlation between training/degradation behavior and fabrication condition of the magnets was studied. The test magnets that had the smaller aspect ratio, a low winding tension, and a high copper ratio and were impregnated with epoxy resin showed no premature quenches and reached critical current at first charging.         Investigation of wire motion in superconducting magnets    T. Ogitsu, K. Tsuchiya and A. Devred Summary: A technique was developed which allows the direct observation of the EMF induced by wire motion and the calculation of the energy release resulting from the motion. Measurements made on a superconducting quadrupole magnet showed that the excitation is accompanied by a great number of wire-motion events of a typical duration of 100 mu s and a typical energy release per unit cross section of 1 mJ/mm/sup 2/. A simple stability model based on the motion of a single strand over a half-twist pitch was then developed. The model could account for the order of magnitude of the energies involved.         Magnetic field dependence of RF surface impedance    M.W. Coffey and J.R. Clem Summary: The surface impedance, Z/sub s/, is calculated for type-II superconductors subjected to a static magnetic field and small-amplitude microwave radiation. A complex penetration depth is calculated by using a model of vortex dynamics including a linear pinning restoring force and a viscous drag force. The static magnetic field dependence of the surface resistance, R/sub s/ and the surface reactance, X/sub s/, is found by examining the dependence of the complex penetration depth on the length scales for low-field penetration, pinning penetration, and flux-flow penetration. In turn, from R/sub s/, the static magnetic field dependence of the rate of energy dissipation is found.         Optimal design of superconducting coils for quench    M. Chew, J.E. O'Meara, W. Tuzel and R.C. Zhou Summary: Analysis of quench phenomena within a superconducting coil can be simulated using a version of M.N. Wilson's QUENCH code (1983). To design a superconducting coil adequately, the event of quench must be anticipated. Quench characteristics are controlled by several parameters, such as coil dimensions, proportion of copper, fraction of superconductor, current density, and unit cell area. The criteria are to minimize the internal voltage and the maximum temperature rise in the superconducting coil during quench. An excessive temperature may cause overheating, thereby damaging the insulation or conductor. To obtain the optimum design parameters for a given magnet, an optimization code has been introduced. With the automatic changing of design variables within the program, the goal of minimizing the internal voltage and/or maximum temperature rise can therefore be attained. The programs OPT-SINGC and OPT-MULTC have been written to approach the design of such superconducting coils using optimization. These codes are capable of designing a system that consists of just a single coil or of multiple coils connected in series.         Temperature dependent parameters of stability and protection in an adiabatic niobium titanium coil    J.N. Brown IV, Y. Tahara, J.E.C. Williams and Y. Iwasa Summary: Experiments were performed to determine temperature-dependent parameters of stability and protection in a small adiabatic niobium titanium test magnet. Quench propagation velocity and minimum quench energy were measured as a function of operating temperature, transport current, and magnetic field. The operating temperature was controlled in an isothermal environment between 4.2 K and approximately 8 K. A computer code was modified to predict the magnet's behavior accurately within the temperature range. The aim was to develop improved analytical models of the effect of temperature parameters on stability in order to expand the understanding of the thermal behavior of adiabatic magnets operating at temperatures up to approximately 100 K.         Stability against the frictional motion of conductor in superconducting windings    T. Takao and O. Tsukamoto Summary: An experiment was performed to investigate quenches of superconducting wires caused by conductor motions. In the experiment, the disturbance energies of conductor motions causing quenches were measured. The conductor moved in a series of step motions, which was demonstrated by the acoustic emission (AE) measurement. A disturbance where the conductor moved at three spacers caused a quench, whereas a conductor motion at one spacer did not trigger a quench. Experimental data are compared to the values derived from the theory, which quantitatively estimate the size of the conductor motion. The theory estimates the disturbance energy quite well.         Design considerations for an inductive heater for conductor stability testing    S.D. Peck and H. Gurol Summary: A discussion is presented of the considerations and the lessons learned in designing inductive heaters for stability testing of a 200-kA conductor for superconducting magnetic energy storage (SMES). Two separate tests were run using different inductive heater designs: the first was a long heater about a subcable pitch in length (50 cm) and was wound with inner and outer coils with currents flowing in opposite directions to minimize stray fields; the second was a short coil about 2 cm long without an inner coil. The thermocouples were used in both tests to measure the total energy delivered to the conductor. In order to calculate the stability margin, it is necessary to know the energy delivered per unit volume of conductor. For the long heater with inner and outer coils, the energy distribution has been calculated to be fairly uniform along the length of the heater. However, for a single short heater, the losses are distributed in a very non-uniform fashion; in fact, they are considerably higher at the test conductor ends due to coupling losses induced by the radial field component. Another design consideration in the test was to let the LRC circuit ring, with the hope of increasing the efficiency of energy transfer to the test conductor. The main conclusions of this study are that the induced heating in the test conductor will depend on the cabling geometry, resistance, and applied field distributions and that great care must be taken to correctly interpret stability margin results based on inductive heat input to very large cabled conductors.         Losses of superconducting conductors for Large Helical Device    T. Kawashima, F. Sumiyoshi, N. Oohito, T. Nagase, T. Mito, J. Yamamoto and K. Takahata Summary: A numerical calculation of pulsive losses in the superconducting conductor to be used for the large helical coil system of the Large Helical Device (LHD) project was performed. The monolithic conductors of the pool-cooled type are stabilized by a large amount of aluminium. A study was made of four kinds of R&D conductors in different locations and of different aluminium stabilizer shapes. It was found that the value of the losses depends not only upon these factors but also upon the cabling condition of the superconducting strand bundle. Optimization of the conductor design is proposed.         Minimum quench energy measurement of NbTi wires using a small ceramic heater    K. Yoda and M. Morita Summary: A small ceramic chip resistor is proposed as a possible ideal point heater for transient stability measurements of superconductors. Preliminary results were obtained using a 1-mm*1.5-mm*0.5-mm ceramic resistor and NbTi wires whose copper-to-superconductor (Cu/SC) ratios were 1 and 2, having the same SC areas. The resistor was soldered on the NbTi wire to minimize the thermal resistance between the resistor and the wire. The minimum quench energy of the Cu/SC ratio 2 wire was approximately twice as large as that of the Cu/SC ratio 1 wire, under the same background magnetic field and with the same ratio of the operating current to its critical current.         AC loss measurements of Nb/sub 3/Sn wire carrying transport current    C.Y. Gung, M. Takayasu, M.M. Steeves and M.O. Hoenig Summary: The AC losses of internal-tin Nb/sub 3/Sn wires have been measured by an isothermal calorimetric method in triangular-wave fields at ramp rates of up to 1.2 T/s and in small-amplitude ripple fields biased with DC fields of up to 9 T. Measurements were made both with and without transport currents, which were both AC and DC. Without transport currents, losses had near-parabolic profiles when plotted against bias field with constant ripple amplitude, against triangular-wave ramp rate, or against triangular-wave ramp amplitude. With transport currents of up to 90% of critical, losses for triangular-wave field were shown to increase up to 17% with increasing DC currents and up to 10% with increasing AC currents. With DC transport currents, the scaling of loss by (1+i/sup 2/), where i is the ratio of transport current to critical current, may be a good approximation.         Hysteretic surface effects in multifilamentary NbTi wires exposed to transverse applied fields    M.D. Sumption, K.R. Marken Jr. and E.W. Collings Summary: Discrepancies in the magnetic hysteresis have been found between bare and clad samples of fine filamentary, multifilamentary, NbTi wires. This difference manifests itself as a greater hysteresis loss in bare than in clad filaments that is significant even in the transverse field orientation. These effects are investigated over a wide range of samples, and for various filament diameters. The dependence of these losses on the orientation of the field with respect to the filaments is studied as well. These effects are attributed to interface pinning.         Magnetization and critical current density of ultra-fine multifilamentary superconducting wires    P. Estop, J.P. Tavergnier, G. Agnoux, A. Fevrier and A. Lacaze Summary: Multifilamentary superconducting wires with a greatly reduced level of losses have been produced with lengths of several tens of kilometers. In spite of the reduction of the filament diameter, proximity effects are avoided, and the best possible use of the reversible motion of the flux lines is made, so that the hysteretic losses are reduced. The concepts lead to a realization of conductors comprising filaments of Nb-Ti (0.1-0.2- mu m diameter) embedded in a highly resistive CuNi matrix. In order to characterize the possible application to industrial power systems, it is necessary to investigate the losses in submicrometric filaments. It is possible to determine the correct value of the critical current density with critical current measurements and magnetization curves on such wires.         AC losses in high-temperature superconductors    K.H. Muller Summary: Intergranular and intragranular AC losses in the superconducting state of ceramic high-temperature superconductors are calculated using a critical state model for the intergranular loss contribution that is similar to that of Y.B. Kim et al. (1963) and the model of C.P. Bean (1962) for the intragranular loss. Good agreement with experimental data over a magnetic field range of 10/sup -4/ T to 10 T is achieved. The effects of sample size, average grain size, and temperature are investigated. In addition, the influence of a DC field on the intergranular AC loss is discussed.         Coils performances of superconducting cables for 50/60 Hz applications    A. Lacaze, Y. Laumond, A. Tavergnier, T. Verhaege, B. Dalle and A. Ansart Summary: Multifilamentary superconducting wires with a greatly reduced level of losses have been produced with unit lengths of several tens of kilometers. With the reduction of the filament diameter, proximity effects are avoided and maximum advantage is taken of the reversible motion of flux lines, so that the hysteretic and matrix losses are lower. These concepts have led to the manufacture on an industrial scale of three wires comprising 377982, 597102 and 920304 filaments of NbTi with a diameter of 0.14 mu m and a 0.13- mu m spacing between the filaments. The matrix material is 30%-Ni-content copper-nickel. Cables made from six such insulated wires have been made with more than 1-km kilometer unit lengths. Numerous impregnated and nonimpregnated coils have been wound with single strands and 6+1 cables. A report is presented on 50-Hz and DC quench currents, 50-Hz AC losses, and 50-Hz electromagnetic stability results. These results are analyzed taking into account proximity effects, reversible motion of flux lines, current sharing, and the thermal behavior of the coil.         Nb/sub 3/Sn superconducting coil for AC use    T. Kishida, T. Kaito, D. Minakuchi, M. Morita, T. Yamada, A. Ohara, F. Fujiwara, K. Yoshizaki and Y. Fujiwara Summary: Nb/sub 3/Sn superconductors were developed for AC use, and a coil was fabricated. The Nb/sub 3/Sn superconductors were manufactured using the internal diffusion process. To reduce AC losses, the spacing between Nb filaments was designed to be 0.5 mu m; consequently, the space factor of Nb filaments was 6%. The diameter of a strand was 0.2 mm, and the diameter of a Nb filament was 0.4 mu m. AC losses in the strand were 180 kW/m/sup 3/ at 0.5 T (60 Hz, peak value). A coil was made using the wind-and-react method using conductors composed of 7*7 strands. The Specifications of the coil were an inner diameter of 156 mm, an outer diameter of 188 mm, a height of 34 mm, and a number of turns of 17 turns*4 layers. To reduce wire motion, the coil was impregnated with epoxy resin. The quench current for DC operation was 1280 A, and the maximum magnetic field of the conductors was 1.6 T. Coil degradations were not observed. The magnet was tested under AC 60-Hz operation. The quench current was 340 A (r.m.s.). The cause of quenching is thought to be the temperature rise of the conductors due to coupling losses among the strands.         Critical current capacity of superconductors at different AC frequencies    V.R. Karasik, V.S. Vysotsky, S.G. Derjagin and V.N. Tsikhon Summary: The measurement of quench currents of sample coils at frequencies from 0 to 1000 Hz in an external magnetic field are presented. Coils were wound with multifilamentary Nb-Ti wires with various diameters in pure high-resistivity matrices with different resistivities. The influence of cooling on quench in the AC mode was studied. The stability of the wire increased with improved cooling and increased magnetic field. Results were analyzed from the point of view of the theory of stability, which takes into account real voltage-current characteristics of the wires.         A new test setup to measure the AC losses of the conductors for NET    G.B.J. Mulder, H.H.J. ten Kate, A. Nijhuis and L.J.M. van de Klundert Summary: A description is given of a new test system currently under construction. The system will be used to measure the AC losses of subcables from Next European Torus (NET) conductors. A special feature of the test arrangement is that the losses will be determined while the sample carries a transport current and is at the same time subjected to a changing magnetic field in the transverse and longitudinal directions. Several aspects of the design, such as magnetic field, forces, and losses, are discussed.         Theoretical and experimental approach to AC losses in a 40 kA cable for NET    D. Ciazynski, J.L. Duchateau and B. Turck Summary: For NET (Next European Torus) application, a 40-kA cable in conduit is being developed. The fabrication technique is expected to be applicable to both NbTi or Nb/sub 3/Sn strands. To ensure good overall mechanical behavior of the cable the number of cabling stages has been limited to three and no full insulation has been provided between stages. A theoretical approach to losses has been developed from the basic multifilamentary strand to the last stage, taking into account the complex combined effect of the different twist pitches. Through this evaluation, the contact resistance and the action of stainless steel spacers for the last stage turn out to be sufficient to limit AC losses to an acceptable level in relation to NET specifications. The theoretical approach has been assessed by several experiments: measurements of AC losses on the basic 1.9-mm strand, on triplets, and on six-around-one subcables in relation to compression; measurements of contact resistances in different cases; and evaluation of the action of chrome plating.         Critical currents and AC losses on subsize cables of the NET-EM/LMI 40-kA Nb/sub 3/Sn cable-in-conduit conductor prototype    R. Bruzzese, S. Chiarelli, P. Gislon, M. Spadoni and S. Zannella Summary: Critical currents have been measured on subsize cables, up to the 27-strand level, of the 40-kA NET-EM/LMI Nb/sub 3/Sn prototype conductor for the OH solenoid of NET (Next European Torus). Energy losses in basic strands were determined by magnetization cycles. Copper and stainless steel were used as conduit materials to produce CIC (cable-in-conduit) conductors with a 0.35 void fraction, which is lower than that of the full-size conductor. The experimental results have shown that, compared to the single-strand current, practically no degradation is observed in cables with a Cu conduit, while the cables with a stainless steel conduit have a critical current lowered by cool-down strain to 0.57 of the expected current in a 27-strand cable at zero intrinsic strain. The measurements of AC losses have indicated high hysteretic losses (effective diameter of =70 mu m). Coupling losses are expected to be negligible.         Magnetic shield of high-T/sub c/ Bi-Pb-Sr-Ca-Cu-O superconductors at 77 K for SQUID measurements    K. Hoshino, H. Ohta, E. Sudoh, K. Katoh, S. Yamazaki, H. Takayama, H. Takahara and M. Aono Summary: The authors have developed a relatively large high-T/sub c/ Bi-Pb-Sr-Ca-Cu-O superconducting magnetic shield vessel of 150 mm in inner diameter, 320 mm in depth, and 10 mm in thickness. It is applicable to biomagnetic measurements with a SQUID. Magnetic fields inside the vessel were measured by using a RF SQUID magnetometer or measuring induced voltages in a pickup coil. The shielding factors, defined as the ratio of the magnetic field at 290 K to that at 77 K, were around 10/sup 5/-10/sup 6/. The magnetic shielding of high-T/sub c/ superconductor is promising for neuromagnetic measurements with SQUIDs.         Some problems of coupling loss calculations, in superconducting cables    S. Takacs Summary: The general solution of the Laplace equation was used to calculate all contributions to coupling losses in single-layered flat and round cables with or without a central insulating layer. The total losses for different cases are compared, and it is concluded that to decrease the coupling losses in flat cables it is necessary to include an insulating layer in the core, whereas this is of little help for the round cable. In the latter case, the increase of the core resistance (and, of course, the increase of the transition resistance between the strands and the core) is much more effective for decreasing the coupling losses.         Fabrication and characterization of high T/sub c/ superconducting magnetic shield    R. Chandra, A.K. Gupta, N. Khare, V.S. Tomar, S.K. Arora, V.N. Ojha, B.S. Khurana, S. Singh and B.K. Das Summary: Superconducting magnetic shields of Y-Ba-Cu-O superconductor were fabricated in tubular form with one end closed. These shields were used successfully to reduce the flux noises of a two-hole RF SQUID of Y-Ba-Cu-O superconductor. Hysteretic critical current density and penetrated field amplitude under increasing and decreasing magnetic fields reveal the presence of grain boundary weak links. The flux trapping behavior can be explained by using a modified version of C.P. Bean's self-field-limiting model (1962).         Design status of superconducting Large Helical Device    O. Motojima Summary: The Large Helical Device (LHD) is a superconducting heliotron/torsatron device. The SC coil system is composed of l=2 helical coils and three sets of poloidal coils with a total stored magnetic energy of 1.63 GJ. The m-number, l-number, major radius, coil minor radius magnetic field, plasma minor radius, and plasma volume are 10, 2, 3.9 m, 0.975 m, 4 T, 0.65 m, and 30 m/sup 3/, respectively. This is an alternative toroidal device which aims at producing plasmas extrapolatable to the reactor regime. The currentless steady operation is the final goal of the LHD program, and there is no danger from the major current disruptions. The material of the superconductor is NbTi, and the cooling systems are pool boiling for helical coils and forced flow for poloidal coils. Since the current density of the helical coils is as high as 53.3 A/mm/sup 2/ with a maximum experienced magnetic field strength of 9.6 T, refrigeration with superfluid helium is required. The LHD has a divertor to control the steady particle recycling and to improve the confinement potential. The vacuum vessel has a dumbbell-shaped poloidal cross section, which makes it possible to install the closed divertor chamber. The necessary R&D programs and detailed design are described.         Superconducting coil design for Large Helical Device    J. Yamamoto, O. Motojima, T. Satow and T. Mito Summary: The superconducting coil design for the Large Helical Device, an interuniversity magnetic confined fusion research device, is described. The major and minor radii of the helical coil are 3.9 m and 0.975 m, respectively. The helical coil is made of a pool-cooled conductor, and the field experienced by the conductor is 7.2 T at phase I and 9.6 T at phase II. Three pairs of poloidal coils are also superconducting. The coils will be made of NbTi conductor.         Development of superconducting conductors for Large Helical Device    T. Mito, J. Yamamoto, K. Takahata, N. Yanagi and O. Motojima Summary: The superconducting helical coils of the Large Helical Device (LHD) require superconducting conductors with large current capacities (from 20 kA to 30 kA) and high current densities (55 A/mm/sup 2/ at 8 T). An NbTi superconductor/bin with pool boiling is being used because of the large electromagnetic force and the complicated helical windings. Several conductors are designed to show how the difference of the position of pure aluminum in the conductors affects the stability and the mechanical properties. Scaled-down R&D conductors with operational currents from 7 kA to 10 kA were made on an experimental basis. The superconducting characteristics, stability, and mechanical properties of these scaled-down conductors were tested. The design and the test results concerning the superconducting characteristics are described.         Development of forced-cooled superconducting coil for Large Helical Device    Y. Wachi, M. Shimada, K. Nakamoto, M. Shibui, T. Hamajima, S. Ioka, O. Motojima, J. Yamamoto, M. Takeo, T. Mito and K. Takahata Summary: A force-cooled superconducting coil has been studied for the Large Helical Device (LHD), which will be a main experimental apparatus of the Japanese National Institute for Fusion Science (NIFS). To achieve the main requirements for the LHD, a large-current, high-current-density NbTi cable-in-conduit-type conductor of 10 kA and 47 A/mm/sup 2/ at 8 T was developed. The test coil was wound in the form of a one-layer solenoid and tested at an operating current of 10 kA in a superposed field of about 7 T, at a hydraulic condition of 1.0 MPa, 4.5 K, and 10 g/s supercritical helium. The stability, normal propagation velocity, and pressure rise during a quench for the high-current-density case were also studied.         Development of 70 MW class superconducting generators    T. Ohara, H. Fukuda, T. Ogawa, K. Shimizu, R. Shiobara, M. Ohi, A. Ueda, K. Itoh and H. Taniguchi Summary: The application of superconductivity technology to electric power apparatus is very important for promoting the conservation of energy and resources. Generators using superconductors as the field windings have many merits compared with conventional generators. A description is given of the basic designs and the current status of R&D work on 70-MW-class superconducting generators. The objective of this work is a 200-MW-class superconducting generator.         Self energized air core superconducting (SEAC) motor    M.A. Hilal, J.D. Lloyd, A.D. Crapo and X. Huang Summary: The SEAC motor described utilizes superconductive windings both for the stator and the rotor and operates the same way as a conventional motor by supplying power to the stator. The rotor of a simple SEAC motor has a small and a large winding and two switches. The axes of the two rotor windings are normal to each other. The rotor is initially stationary, and the windings are exposed to the rotating stator field. Flux pumping is employed to charge the rotor windings. As the field rotates by 180 degrees from being parallel to the axis of the small winding of the rotor, a switch connected in series with the windings automatically opens, allowing the magnetic flux to penetrate the winding. The switch is closed during most of the other half of the cycle. The flux trapped in the small winding is partially transferred to the larger rotor winding by opening another switch, which results in series connection of the two windings. This results in charging the large winding and in accelerating the rotor to reach the rotating field angular velocity. The rotor synchronously rotates with the field when steady-state operation is achieved. The use of a high-temperature superconductor allows the persistent operation of the rotor windings after reaching steady state.         Homopolar DC motor and trapped flux brushless DC motor using high temperature superconductor materials    A.D. Crapo and J.D. Lloyd Summary: Two motors have been designed and built for use with high-temperature-superconductor (HTSC) materials. They are a homopolar DC motor that uses HTSC field windings and a brushless DC motor that uses bulk HTSC materials to trap flux in steel rotor poles. The HTSC field windings of the homopolar DC motor are designed to operate at 1000 A/cm/sup 2/ in a 0.010-T (100-G) field. In order to maximize torque in the homopolar DC motor, an iron magnetic circuit with small air gaps gives maximum flux for minimum Ampere turns in the field. A copper field winding version of the homopolar DC motor has been tested while waiting for 575 Ampere turn HTSC coils. The trapped flux brushless DC motor has been built and is ready to test melt textured bulk HTSC rings that are currently being prepared. The stator of the trapped flux motor will impress a magnetic field in the steel rotor poles with warm HTSC bulk rings. The rings are then cooled to 77 K to trap the flux in the rotor. The motor can then operate as a brushless DC motor.         Development of superconducting linear induction motor for steel making processes    O. Tsukamoto, Y. Tanaka and S. Sato Summary: A superconducting linear induction motor (SLIM) is being developed for steel-making processes using ultrafine filamentary NbTi wires. A SLIM can produce a strong magnetic field and large thrust in a wide gap. Applying SLIMs to a steel making plant could result in important innovations. A model of the SLIM has been made and tested. The model SLIM worked in a frequency range of 20-30 Hz. The feasibility of a SLIM as hardware has been demonstrated.         Analysis and performance of an axial-gap superconductor motor    R.A. Hawsey, W.K. Kahl, S.W. Schwenterly, J.M. Bailey, C.W. Sohns, J.N. Luton, B.W. McConnell and V.W. Campbell Summary: The performance of a variable-speed, AC, superconducting motor has been evaluated. A novel axial-gap geometry was chosen for four-pole, 1800-r/min operation, using a superconducting stator and normal armature. The pool-boiling cryostat contains four solenoidal field windings of filamentary Nb-Ti conductor and has a maximum field of 7 T and an air-gap field of 2-3 T. The armature windings are formed from copper Litz wire and are arranged in 48 radial slots. The wires inside diameter and outside diameter are 17.18 and 69.24 cm, respectively. The armature is driven by three-phase power supplied via slip rings and an adjustable-speed drive. The maximum design power is 100 hp, which can be doubled by using two armatures. Motor-performance data as a function of speed and air-gap flux density are presented for initial low-power tests with a drive capable of delivering 60 A per phase to the armature.         Electrical tests on a fully superconducting synchronous machine    P. Tixador, Y. Brunet, P. Vedrine, Y. Laumond and J.L. Sabrie Summary: The emergence of ultrafine multifilamentary superconducting wires with very low losses under varying magnetic fields allowed the testing in 1987 of a three-phase 50-Hz superconducting stationary winding with a classical copper/iron rotor. A superconducting field rotor was constructed and mounted into the previous stator to form a fully superconducting machine. The rotating part is rather simple: a helium vessel rotates into a low-pressure vessel to avoid thermal losses by turbulence. There is no thermal shielding due to the cryogenic environment of the stator, and the electromagnetic shield, present in classical superconducting generators, has been avoided with the low loss superconductors used. The combined 900-mm-long, 320-mm-diameter, rotor-stator cryostat uses fiberglass composites in the central parts due to the rotating fields under permanent or transient operations. The first electrical tests of this small-scale 18-kVA machine under permanent and sudden-short-circuit tests are reported.         A comparison of ASTROMAG coils made with aluminum and copper based superconductor    M.A. Green Summary: The use of an aluminum matrix superconductor in the coils for the ASTROMAG magnet will increase the integrated field for conducting particle astrophysics experiments in space as compared to equal mass coils made with a copper matrix superconductor. The increased ability to detect charged particles can be achieved without decreasing the current margin of the superconductor in the coils. The use of a low-resistivity aluminum matrix conductor increases the energy needed to initiate a quench by two orders of magnitude. The current decay time constant during a quench is substantially increased. As a result, the quench energy dumped into the helium tank is reduced (the ASTROMAG coils are thermally decoupled from the helium tank), and the forces on the shield and shells due to eddy currents will be lower. A description is also given of the problems associated with the use of an aluminum matrix superconductor in the coils.         Design of an opposing pair magnet system for ASTROMAG    P.G. Marston, J.R. Hale, R.F. Vieira, A. Zhukovsky, P. Titus, J. Sullivan and A. Dawson Summary: A magnet system comprising a pair of self-supporting disk-shaped coils has been designed for the ASTROMAG facility on the space station Freedom. The coils are connected in a quadrupole configuration in order to eliminate their dipole moment. One of the primary requirements of this design is that the magnet coils must have near-perfect structural integrity. To this end, each coil would be manufactured as a monolithic composite in which the superconducting wire is incorporated as one of the components. By utilizing a precision X-Y numerically controlled wiring machine, the coil can be built up in pancake layers by alternating prepreg sheets of fiber/epoxy (e.g. carbon or Kevlar fiber) with a layer of NbTi wire that spirals from OD to ID in one layer, from ID to OD in the next. and so on. Each disk magnet will have an ID of 0.4 m and an OD of 1.7 m. The peak field at the winding will be 7.2 T. The system is to operate at 1.8 K. and I/sub op//I/sub c/=0.5. Results of magnetic field and force calculations are presented, and the structural characteristics of the system are described.         Superferric magnets for fast levitated trains    F.R. Huson, W.W. Mackay, Y. Miao, S. Pissanetzky and Y. Xiang Summary: A new technology for high-speed magnetically levitated train (MAGLEV) transportation is being developed. The technology is based on self-shielded superferric magnets which provide guidance and levitation at above 50 mph'. A linear motor is used for propulsion. The levitation and guidance superconducting magnets are distributed along the entire length of the cars. The superferric magnet shields the fringe field within the car to less than 5 G. Magnetic details and initial calculations of dynamics are presented.         Superconducting magnet and on-board refrigeration system on Japanese MAGLEV vehicle    H. Tsuchishima and T. Herai Summary: Running tests on the Miyazaki test track are repeatedly carried out to speeds over 300 km/h using the magnetically levitated (MAGLEV) vehicle MLU002. The development of the MAGLEV system for the new test line has already started, and a new superconducting magnet for it has been manufactured. An onboard refrigerator is installed in the superconducting magnet to keep the liquid-helium temperature without the loss of liquid helium. The helium gas produced when energizing or deenergizing the magnet is stored in onboard gas helium tanks temporarily. The onboard refrigerator is connected directly to the liquid-helium tank of the magnet. Thus, the stored helium gas can be reliquefied easily by the onboard refrigerator. In order to minimize the volume of the helium gas produced when energizing and deenergizing the magnet, the power leads of the magnet, superconducting coils and persistent current switches have been improved. The energization and deenergization of the magnet can be finished in 1 to 2 min.         Development of the superconducting magnet system for industrial high gradient magnetic separator    Yan Luguang, Yi Changlian, Yu Yunjia, Cai Genxin and Tu Guibing Summary: To promote the effective development of superconducting magnetic separation technology and its practical industrial application for kaolin clay beneficiation, an industrial prototype superconducting magnetic separator is being developed. For this reciprocating-type separator with a horizontal axis, a superconducting magnet system consisting of a 0.5-m warm bore, a 0.8-m-long, 4-T central field high-current-density superconducting solenoid, a horizontal dewar, and a 10-L/h close-loop helium liquefier is under development. The main considerations in design and experience in development and construction are summarized.         Development of a compact 18-T MF-(NbTi)/sub 3/Sn coil    M. Nishi, T. Isono, Y. Takahashi, T. Ando, H. Tsuji, T. Uchiyama, N. Aoki, M. Ichihara and E. Suzuki Summary: The magnetic flux density of 18.4 T at 4.2 K was obtained by a 32-mm-bore superconducting coil wound with two grades of tube-processed multifilamentary (NbTi)/sub 3/Sn superconductors in a background field of 13.2 T. The average current density values of this coil were 70 A/mm/sup 2/ in the 18.4 T region and 107 A/mm/sup 2/ in the region less than 16.7 T. The energy stored in the 18-T coil system including background field coils was only 1.48 MJ at 18.4 T. The charging time of this system from 0 T to 18 T is only 12 min. This success encourages the development of high-performance superconductors for the high-field large coils of future thermonuclear fusion machines.         Research and development of superconducting helicoids    V.E. Keilin, I.A. Kovalev, N.F. Kopeikin, S.L. Kruglov and D.B. Pavin Summary: Superconducting helicoids, i.e., magnets with planar turns, are in the process of being developed. Their main advantages are: high mechanical rigidity, the possibility of current redistribution across the turn width in accordance with magnetic field value, and the possibility of utilizing superconductors in nontraditional forms different from the usual wires, cables, and tapes. In the future this possibility may be of special importance for utilizing high-temperature superconductors. Shortcomings of the superconducting helicoids are also mentioned. They are thermomagnetic instability and electrical losses, both resulting in charging rate limitations. The design and test results of model helicoids are presented: a NbTi coil with ID=180 mm OD=320 mm: a NbTi racetrack with large and short axes of 120 mm and 48 mm, respectively; and a Nb/sub 3/Sn coil with ID=46 mm, OD=120 mm. The racetrack winding without any bandages reached its critical parameters almost without training. The charging rate of the Nb/sub 3/Sn helicoid was much higher than that of NbTi coils. The total induction of the Nb/sub 3/Sn coil tested in a bias field was about 10.5 T.         Large aperture superconducting cryostable quadrupoles for CEBAF's high momentum spectrometer    S.R. Lassiter, P.D. Brindza, W.T. Hunter, R.R. Thorpe, M.J. Fowler and J.A. Miller Summary: The current design for the Hall C High Momentum Spectrometer calls for two large-aperture quadrupoles, each having the same physical characteristics but operating at different field gradients. A cold-iron, superconducting, laminated yoke magnet has been developed as the reference design. The results of the two- and three-dimensional magnetostatic studies are presented along with some details of the conductor and cryostat design.         Cryostat design and magnetostatic analysis of the 6 GeV superconducting dipole for the CEBAF high momentum spectrometer    J.A. Miller, P.D. Brindza, M.J. Fowler, W.T. Hunter, S.R. Lassiter and R.R. Thorpe Summary: The dipole for the Hall C High Momentum Spectrometer is a 470-ton, superconducting, cryostable magnet. With a bend radius of 12.05625 m and an effective length of 5.26 m, it is configured to achieve a 25 degrees bending angle for 6-GeV/c momentum particles over its 42-cm gap at a central field excitation of 1.66 T. The thermal syphon cooled coil consists of three double pancakes of 3-kA copper-stabilized conductor. The cryostat consists of this cryostable coil wound directly onto a stainless steel bobbin with G-10 support cylinders connected to the bobbin to transfer loads produced during energization to the yoke iron, and a stainless steel heat transfer panel cooled by LN/sub 2/ and a stainless steel vacuum vessel. The coil assembly is suspended within the vacuum vessel by eight tensioning support links.         Design of the superconducting 45 degree dipole for the CEBAF high resolution spectrometer    A.R. Gavalya, J. Alcorn and W. Tuzel Summary: The 460-ton dipole for the Hall A 4-GeV/c High Resolution Spectrometer has a bend angle of 45 degrees , with an 8.4-m radius of curvature and an effective length of 6.6 m. It has a useful width of 100 cm and a 25-cm gap at the central radius of curvature. The dipole provides focusing in the dispersive plane by means of rotated (by 30 degrees ) entrance and exit pole faces as well as a field index of -1.25. The end contour geometries have been designed to eliminate higher-order aberrations. The maximum central field is 1.6 T at 4 GeV/c. A field quality of 2*10/sup -4/ (maximum deviation from the design value) is required over an excitation range from 0.16 T to 1.6 T. The 1.8-kA conductor is a 36-wire flattened cable. It has been designed to have limited cryostability at 4.5 K and 1.3 atm. Each coil is wound as one double pancake against the outer wall of the helium vessel in order to react the in-plane (hoop) loads. The bath-cooled, planar coil features negative curvature on its inner radius and at the exit. The coil produces 400 KAT at full excitation. The stored energy of this magnet is 3.5 MJ.         CEBAF cryomodules: test results and status    I.E. Campisi, R. Ahlman, M. Augustine, K. Crawford, M. Drury, K. Jordan, P. Kelley, T. Lee, J. Marshall, J. Preble, J. Robb, W. Schneider, J. Susta, J. Van Dyke and M. Wiseman Summary: The Continuous Electron Beam Accelerator Facility is under construction in Newport News, Virginia. When completed in 1994, the accelerator will be the largest installation of radio frequency superconductivity. Production of cryomodules, the fundamental cryogenic building blocks of the machine, has started. They consist of four pairs of 1497-MHz, five-cell cavities contained in separate helium vessels and mounted in a cryostat with appropriate end caps for helium supply and return. The first cryomodule has been successfully assembled, tested, and moved to the accelerator. Some of the individual components in this prototype performed below, but close to, the specification. As a whole, the cryomodule performs in a more than acceptable way for operation in the injector. It will provide 20 MeV to the electron beam with a tolerable dissipation of about 75 W at 2 K. A new cryomodule with full production components will replace this prototype.         Stability of large composite superconductors    X. Huang and Y.M. Eyssa Summary: High-current large composite conductors cooled in He II baths are planned for superconductive magnetic energy storage (SMES) systems. Such conductors have long time constant current diffusion causing high initial I/sup 2/R generation when driven normal. As a result, the front of a normal zone may propagate even though the back of the normal zone is recovering as current diffuses deeper (with less I/sup 2/R) into the stabilizer. Accurate knowledge of I/sup 2/R heat generation in the current sharing region and the time-dependent transient heat transfer to helium is determined for the stability analysis. Analytical and numerical procedures are developed to calculate the maximum nonpropagating currents and propagation velocities. Round and rectangular shaped conductors are considered via the computational model. Numerical results are compared with experimental data.         Conductor and vessel losses in bath cooled SMES systems    Y.M. Eyssa Summary: Several AC and DC loss sources are analyzed for superconductive magnetic energy storage (SMES) solenoids cooled in a bath of 1.8-K helium. The AC losses (eddy current losses) in the solenoid of the helium vessel and due to conductor stabilizer coupling loss are calculated for different charge or discharge sequences. The losses in the helium vessel are found for vessels both with and without an electric break. The analysis of DC loss for conductor joints takes into account several NbTi/Cu strands twisted around a high-purity aluminum stabilizer conductor. The resistance of the conductor joint depends on the electrical resistance of the bond between the strand and the aluminum and the distribution of joints staggered in position on the aluminum stabilizer.         Low bending rippled structure design and frictional energy disturbance analysis for superconductive magnet energy storage    X. Huang Summary: Friction between the structure and conductor is the largest potential thermal disturbance to superconductive magnetic energy storage (SMES) conductors. Direct calculation of the disturbance is difficult because input assumptions on friction coefficients and slippage distances are not reliable for a stick-slip occurrence. A general approach is presented in which the disturbance E/sub D/ is calculated as the difference in strain energy before and after slippage, which is independent of the friction coefficient and slippage details. The disturbance is found for the low bending ripple, circular ripple, and nonripple structures. The low bending ripple structure has a very small disturbance, approximately 2% of that for a nonripple structure.         Quench protection for the 21 MWh ETM coil    M.K. Abdelsalam and Y.M. Eyssa Summary: An emergency internal dump procedure and analysis are presented for the 21-MWh engineering test model (ETM) of a full-scale superconductive magnetic energy storage (SMES) coil. The coil is arranged into four modules which can be connected in parallel using cryogenic switches. The first step in the energy dump procedure is to close all switches. The second step is to expel the liquid helium in about 20 to 40 s. As the liquid helium level drops, the current transfers inductively from the uncovered top modules to the other modules. The conductor and parallel structure pieces tend to warm up uniformly with tolerant voltage levels. Two cases are considered: the case where all turns are connected in series (no parallel switching) and the case of the parallel connection of the four modules. A safety analysis of the consequences of a faulty switch is also presented.         Research on power conditioning systems for superconductive magnetic energy storage (SMES)    R.L. Kustom, J.J. Skiles, J. Wang, K. Klontz, T. Ise, K. Ko and F. Vong Summary: Several converter/inverter circuit topologies using silicon controlled rectifier (SCR) and gate turn off (GTO) devices have been developed for operating a superconductive magnetic energy storage (SMES) coil with an electric utility. Control of real and reactive power and shorting switch and current bypass techniques have been investigated. Experimental tests of independent real and reactive power control have been successfully performed using an 8-h superconducting coil and 10-kVA power conditioning circuits. In typical studies, the real power was cycled from zero to a peak charging power of 7 kW and then the discharging power was held constant at 3 kW, while the reactive power was independently held constant at various values between 0 and +or-5 kvar. A technique for zero current opening of a mechanical bypass switch using converter control to cancel the coil current in the closed bypass switch was also successfully demonstrated using the 8-h coil.         A comparison of large-scale toroidal and solenoidal SMES systems    S.M. Schoenung, W.R. Meier and W.V. Hassenzahl Summary: A review is presented of the characteristics of large-scale toroidal and solenoidal coils (>10 MWh, or 36 GJ) to establish a basis for quantitative estimates of the material requirements for these two SMES (superconducting magnetic energy storage) systems. The size dependence, the scaling features, and the estimated costs for major material components are compared. Results show that requirements for major materials in the toroid exceed those for the solenoid by factors from two to more than five, depending on size and assumptions.         Conceptual design of a 100 MJ superconducting magnetic energy storage    V.V. Andrianov, V.M. Batenin, A.S. Veselovsky, I.A. Kiryenin, S.I. Kopylov, Y.A. Bashkirov, V.V. Sytnikov, A.S. Rychagov, N.S. Lazarev and A.V. Stukachev Summary: The conceptual design of the 100-MJ SMES (superconducting magnetic energy storage) test facility is described. The facility's rated steady conditions correspond to a peak current of 5 kA in the winding, which is fully stabilized at a 4-T field and a 50-MJ capacitance, and to a converter power of 20 MW. Under forced conditions (1 h) the peak current rises to 7.1 kA and 5.6 T (a partially stabilized winding) at a stored energy of 100 MJ and a converter power of 30 MW. The winding is made from a multistrand transposed cable (Nb-Ti+Cu).         Development of a thermally switched superconducting rectifier for 100 kA    G.B.J. Mulder, H.H.J. ten Kate, H.J.G. Krooshoop and L.J.M. van de Klundert Summary: A full-wave superconducting rectifier for 100 kA has been developed. Typical design values of this device are: a secondary current of 100 kA, a primary amplitude of 20 A, an operating frequency of 0.5 Hz, and an average power on the order of 100 W. The rectification is achieved by means of thermally controlled superconducting switches with recovery times of 150 to 300 ms. A description of the rectifier system is given. The first experiments, in which the rectifier was tested at up to 25 kA demonstrate reliable and fail-safe operation of the rectifier at lower current levels. It was, for example, successfully used to load and unload a 25-kA coil at a rectifier frequency of 0.4 Hz and an average power of 30 W. During tests without any load, it was found that the secondary circuit of the transformer quenches at about 60 kA. Therefore, it is unlikely that the rectifier in its present configuration will attain 100 kA.         Observations of flux motion in niobium films    Y.M. Xiao and G.M. Keiser Summary: A magnetic field trapped in a superconducting sphere was examined at temperatures from 4.6 K to 5.5 K. The sphere was the rotor of a precision gyroscope and was made of fused quartz and coated with a sputtered niobium film. The rotor diameter was 3.8 cm. The film thickness was 2.5 mu m. The tests were carried out at an ambient magnetic field of about 1 mG. Unexpected instability of the trapped field was observed. The experimental results and possible explanations are presented.         Fundamental test of new DC superconducting fault current limiter    T. Ishigohka and N. Sasaki Summary: A novel superconducting DC fault current limiter (SCDCFCL) for suppressing a short-circuit current in a DC transmission line is presented. The SCDCFCL is composed of two superconducting windings wound on a single iron core. A small experimental SCDCFCL was fabricated, and the fundamental operation was confirmed. The experimental results are presented. Considerations for a future full-size design are also presented.         Superconducting fault current limiter development    D. Ito, K. Tsurunaga, E.S. Yoneda, Y. Sugiyama, T. Hara, K. Okaniwa, H. Hoshino and T. Yamamoto Summary: The authors have developed and tested a 400-V 100-A-class fault current limiter wound with AC superconducting wire with ultrafine NbTi filaments. The limiter consists of noninductively wound superconducting trigger coils and a superconducting limiting coil which acts as a reactor. Excessive fault currents initiate quenching in the trigger coils and these currents, which have flown in trigger coils in nonfault conditions, are commutated from the trigger coils to the limiting coil. In an experiment, a fault current level was successfully limited to 120 A with a limiter whose terminal voltage at the limiting condition was 420 V.         Fundamental analysis of dynamic stability in superconductive power systems    Y. Mitani, K. Tsuji and Y. Murakami Summary: The features of instability in a long-distance bulk power transmission model system with superconductive power transmission lines or with superconductive synchronous generators are analyzed numerically. It is shown that self-excited oscillation is easily induced in superconductive AC power transmission systems. Torsional oscillation and electromechanical power swing in a model power system with a superconductive turbine generator power plant are analyzed for various system conditions, and it is confirmed in a digital simulation study that adequate energy control of the field winding of a superconductive generator can stabilize the power system.         Design and fabrication of forced-flow coils as an R&D program for Large Helical Device    K. Takahata, N. Yanagi, T. Mito, J. Yamamoto, O. Motojima, K. Nakamoto, S. Mizumaki, K. Kitamura, Y. Wachi, H. Shinohara, K. Yamamoto, M. Shibui, T. Uchida and K. Nakayama Summary: Two forced-flow cooled NbTi superconducting coils (TOKI-TF, PF) have been designed and fabricated. The helical coil (TOKI-TF) is a 1/4-scale model of the Large Helical Device (LHD). It has a major radius of 0.9 m, a minor radius of 0.25 m, and a pitch number of 4. Nominal current and maximum field were designed to be 8 kA and 2.8 T, respectively. Another coil (TOKI-PF) was fabricated for the demonstration of LHD poloidal field coils. It consists of two double pancakes with an inner radius of 0.6 m and an outer radius of 0.82 m. The nominal current of 25 kA simulates that of LHD poloidal field coils. Cable-in-conduit-type conductors were used for the both coils. The test facility was also constructed with a vacuum vessel, a liquid nitrogen shield, 30-kA power leads, a heat exchanger, and cryogenic supports. Design concepts and details are presented.         Design and fabrication of pool cooled helical coil as an R&D program for Large Helical Device    N. Yanagi, K. Takahata, T. Mito, J. Yamamoto, O. Motojima, R. Saito, S. Suzuki, F. Iida and H. Ogata Summary: A pool-cooled NbTi superconducting helical coil system (named TOKI-HB) has been fabricated as part of one of the research and development programs for the Large Helical Device (LHD). The main purpose of the construction of this device is to build an entire pool-cooled superconducting helical coil system which is large enough to be extrapolable to LHD. The helical coil has a major radius of 0.8 m and a minor radius of 0.2 m with a helical pitch number of 3. An operating current of 8.9 kA produces a maximum magnetic field of 0.75 T at the geometrical center of the poloidal cross section and 3 T at the coil surface. Basic design concepts of the TOKI-HB device are described together with some issues of the fabrication.         Design and fabrication of module coil as an R&D program for Large Helical Device    T. Mito, J. Yamamoto, K. Takahata, N. Yanagi, O. Motojima, T. Ichihara, K. Toyoda, T. Minato and T. Sasaki Summary: A twisted solenoid coil (TOKI-MC) has been designed and fabricated in order to study the mechanical properties of the Large Helical Device (LHD). One of the most important R&D items of the LHD is the mechanical behavior of the helical coils under a large electromagnetic force. The TOKI-MC was wound obliquely on the 3D-machined elliptical bobbin with a maximum torsional rate of 36 degrees /m at the innermost conductor. The maximum field in the coil is 7.7 T with an operating current of 20 kA, an average current density of 40 A/mm/sup 2/, and a stored energy of 11 MJ. The TOKI-MC can simulate the electromagnetic force, conductor torsional rate, magnetic field, operating current, and current density of the LHD superconducting helical coils. The design and test results of the conductor and the design and fabrication of the coil are described.         A conceptual design of the international thermonuclear experimental reactor central solenoid    J.R. Heim and J.M. Parker Summary: One of the central solenoid (CS) designs for the International Thermonuclear Experimental Reactor (ITER) superconducting magnet system is presented. The CS part of this magnet system will be a vertical stack of eight modules, approximately 16 m high, each having approximate dimensions of 4.1-m o.d., 2.8-m i.d., and 1.9-m h. The peak field at the bore is approximately 13.5 T. A cable-in-conduit conductor with Nb/sub 3/Sn composite wire will be used to wind the coils. The overall coil fabrication will use the insulate-wind-react-impregnate method. Coil modules will be fabricated using double-pancake coils with all splice joints located in the low-field region on the outside of the coil. All coils will be structurally graded with high-strength steel reinforcement which is cowound with the conductor. Further details of the CS coil design and analysis are described.         The US demonstration poloidal coil    M.M. Steeves, T.A. Painter, M. Takayasu, R.N. Randall, J.E. Tracey, I.S. Hwang and M.O. Hoenig Summary: The United States Demonstration Poloidal Coil (US-DPC) has been built and will be tested at the Japan Atomic Energy Research Institute (JAERI). The 2-m-diameter, 30-kA, Nb/sub 3/Sn solenoid is designed for 10-T operation with charging and discharging from zero to full field at ramp rates of up to 10 T/s. The fabrication is described. A summary of problems encountered in the manufacture of the wind-react-insulate coil made from cable-in-conduit conductor (CICC) is given.         Design of a 0.6-m bore wind-and-react 12-T, 6-kA, Nb/sub 3/Sn magnet    A. Della Corte, E. Di Pietro, G. Pasotti, N. Sacchetti and M. Spadoni Summary: Design concepts for a Nb/sub 3/Sn wind-and-react (W/R) magnet, wound with a cable-in-conduit conductor, are presented. The magnet is designed to operate at approximately 6 kA, generating a maximum field of 12 T over a 0.6-m bore. The design of the forced-flow-cooled cable-in-conduit conductor, the winding principles, the heat exchanger effect in the magnet, and the stress analysis on the coil and conductor are reported and discussed.         Conductively cooled Nb/sub 3/Sn magnet system for a magnetic refrigerator    J.R. Rowe, J.A. Hertel, J.A. Barclay, C.R. Cross, J.R. Trueblood and D.D. Hill Summary: A Nb/sub 3/Sn magnet system for use in a magnetic refrigerator has been developed and tested. The system incorporates four asymmetric windings arranged as two Helmholtz pairs to produce two profiled field regions, required for a Carnot cycle. System components are cooled by conductive heat transfer to enable eventual operation in vacuum without liquid helium. Design features include low-resistance joints and superconducting interconnecting buses for low-ohmic losses in the persistent mode. The magnets are produced by the wind-and-react method on iron forms, followed by epoxy impregnation. The system requirements and design are described in further detail, and test results are presented.         Three-dimensional thermal stresses in a superconducting coil assembly    C. Minas and L. Salasoo Summary: The three-dimensional thermal stresses in a solenoidal superconducting coil assembly are examined and evaluated. The superconductor composite is modeled as an orthotropic material with three planes of elastic symmetry, with mechanical properties derived from experimental measurements at 293 K and liquid-nitrogen temperature, adjusted according to the applied temperature range. The cooldown stresses in the coil in a stand-alone configuration are compared to the stresses due to the temperature field simulated for a quench. The quench thermal transient analysis creates a nonuniform temperature profile in the range of 30-250 K. A two-dimensional and a three-dimensional temperature field are used in the three-dimensional stress analysis. When comparing the stresses in the cooldown and temperature fields, the results indicate an increase of the tensile hoop stress by a factor of four and an increase of the compressive hoop stress in the coil by a factor of eight. Similar analysis is performed on the superconducting coil assembly, which includes a part of the glass-epoxy composite coil form and the aluminum support structure, and the results are examined and evaluated. The analysis is performed in the cylindrical coordinate system by using the commercial package ANSYS.         A vertically reciprocating NbTi solenoid used in a regenerative magnetic refrigerator    J.R. Trueblood, P.J. Claybaker, J.W. Johnson and T.M. Stankey Summary: An 8.2T-NbTi superconducting solenoid used for periodic magnetization by vertical motion along a bed of magnetocaloric material in a regenerative magnetic refrigerator using all active magnetic regenerator (AMR) has been designed, fabricated, and tested. The magnet design had two primary requirements: field uniformity and minimum stray flux. The magnet is charged with demountable leads and switched into persistent mode. Wheels and tracks guide the magnet in a liquid-helium dewar which is part of a larger environment cooled by a gas cycle refrigerator. Positioning of the magnet is determined by a computer-driven, PI-controlled linear actuator servo. design, test configuration, and test results of the solenoid systems are described.         Superconducting magnet system for an experimental disk MHD facility    H.G. Knoopers, H.H.J. ten Kate, L.J.M. van de Klundert, P. Massee and W.J.M. Balemans Summary: A predesign of a split-pair magnet for a magnetohydrodynamic (MHD) facility for testing a 10-MW open-cycle disk or a 5-MW closed-cycle disk generator is presented. The magnet system consists of a NbTi and a Nb/sub 3/Sn section, which provide a magnetic field of 9 T in the active area of the MHD channel. The optimization process, which is based on minimum conductor costs is discussed, and the proposed conductor design is described. Basic solutions for the construction of the magnet, the cryostat and the cooling technique are also presented.         17 Tesla magnet with 300 mm outer diameter    M. Urata, H. Maeda, N. Aoki and G. Uchiyama Summary: A 17-T superconducting magnet was fabricated and tested. The designed field is 17 T with 160 A in the 33-mm bore at 4.2 K. The magnet is composed of two sets of Nb/sub 3/Sn coils and a NbTi coil graded into two sections. The Nb/sub 3/Sn conductor is a Ti added Nb tube processed conductor, reacted after coil winding. The conductor reaction process was developed to get 880 A/mm/sup 2/ current density without a matrix under 14.5 T and residual resistivity ratio of 87. The stabilization method applied to the coil was a flexibly supported epoxy resin impregnated coil without the mandrel. This method has been developed in the experiments and stress analysis of small NbTi and Nb/sub 3/Sn coils. The current density for the NbTi coil reaches 260 A/mm/sup 2/ at 8.6 T, resulting in the compact system operated in a 300-mm-diameter cryostat. The maximum voltages at coil quenches were as high as 860 V, due to the low-current design.         A test facility for 200 kA SMES/ETM conductors    J. Zeigler, J. Colvin, R. Huson, R. Rocha, G. Shotzman, P. Michels and S. Peck Summary: The test facility and the procedures used to characterize two full-scale copper-stabilized cable-in-conduit superconductors are described. The critical current at 1.8 K was 280 kA at a total field of 5.8 T, 260 kA at 6.4 T, and 215 kA at 7.4 T. The stability margin at 200 kA and 4 to 5 T was 70 to 80 mJ/cm/sup 3/ of metal. No significant performance degradation was observed after more than 600 load cycles.         Development of superconductors for a 70 MW class superconducting generator    K. Yamaguchi, Y. Matsunobu, N. Tada, Y. Yagi and R. Shiobara Summary: Since 1988 a project has been underway in Japan in which superconducting generators for utility applications are being developed. The aim of the project is the development of a 200-MW-class superconducting pilot generator. During development work, of 70-MW-class superconducting, model generators are being run in order to clarify the problems in manufacturing and operating the pilot generator. The design of the model generator and the development of the components, especially the superconductors for the generator are discussed. Details of the development of the superconductor installed in the rotor are described.         Critical current densities and magnetic hysteresis losses in submicron filament bronze-processed Nb/sub 3/Sn wires (1990)    K. Kamata, S. Sakai, K. Tachikawa, T. Taniguchi, T. Ajioka and H. Hatakeyama Summary: Submicron-filament bronze-processed multifilamentary Nb/sub 3/Sn wires with a Cu-5at.%Sn matrix and Nb or Nb alloy cores have been fabricated. The Nb alloy cores each contained 1-at.% Zr, Ti, Hf, or Ta. Among the peripheral-Cu-stabilizer-type wires, the Nb-1Ta core wire showed the highest non-Cu area critical current density, J/sub c/ of 3*10/sup 4/ A/cm/sup 2/ at 12 T after all optimum heat treatment, in spite of its relatively low Sn concentration in the matrix. The deformation of Nb cores into ribbonlike shapes was apparently suppressed by the 1-at.% addition of Ti, Hf or Ta. The values of J/sub c/ per unit magnetic hysteresis loss for the Ti, Hf, and Ta alloyed Nb core wires have been evaluated to be higher than that for the pure Nb core wire. Central-Cu-stabilizer-type wires with the same alloy cores were also prepared. The Nb-1Ta core wire again showed the highest J/sub c/'s. The J/sub c/'s for a Nb core wire increased further because of heat treating after Sn plating. It is shown that the hysteresis loss also decreases when the wire is heat treated after Sn plating, as a result of the increase in matrix resistivity. Thus, the bronze-process-based external Sn diffusion method using Nb alloy cores shows promise for the development of high-current-density and very-low-AC-loss Nb/sub 3/Sn wire.         Magnetization and critical currents of tin-core multifilamentary Nb/sub 3/Sn conductors    A.K. Ghosh and M. Suenaga Summary: Critical current and magnetization data are presented for some multifilamentary Nb/sub 3/Sn wires that have been produced by the internal-tin method. A comparison of magnetization and transport critical current measurements shows that filament bridging during heat treatment is a common occurrence leading to effective filament diameters that are sometimes an order of magnitude larger than the geometrical filament size. At present J/sub c/'s (in the noncopper region) greater than 1300 A/mm/sup 2/ at 10 T have been achieved in some conductors, which also exhibit high losses. Low losses have only been seen in conductors with a high local ratio of copper to niobium. The use of (Nb-1%Ti) alloy instead of pure Nb helps to reduce low-field loss and increase high-field J/sub c./ Measurements of the temperature dependence of hysteretic loss to 5 T indicate that loss decreases linearly with increasing temperature.         Magnetization decay effects in NbTi multifilamentary superconducting wires    K. Matsumoto, A. Takagi, Y. Tanaka and M. Ikeda Summary: The magnetization decay effect over time was studied for NbTi multifilamentary wires of various cross-sectional structures. It was found that the lower the electrical resistivity between filaments and the smaller the spacing between filaments of a specimen, the larger its magnetization decay rate. It was further found that the rate of magnetization decay was anisotropic with respect to the applied field, with rates being higher when the field was applied perpendicular to the wire axis. There was also a dependence of field profile, but results were complicated by supplemental magnetic flux. All these types of behavior were found to be attributable to the presence of a weakly superconductive portion induced by the proximity effect, and were explained by this model.         Characterization of composite high temperature superconductors for magnetic bearing applications    B.R. Weinberger, L. Lynds, J. Van Valzah, H.E. Eaton, J.R. Hull, T.M. Mulcahy and S.A. Basinger Summary: A study of high-temperature superconductor composites for use in magnetic bearings applications is presented. Fabrication and characterization techniques are described. Magnetometry and mechanical force measurements are correlated, with particular emphasis on the role of superconductor particle size. Results are discussed in terms of the fundamental limits of Meissner effect levitation.         Rotational decay torques of superconducting magnetic bearing    R. Takahata and T. Yotsuya Summary: A superconducting magnetic bearing is proposed as one of the applications of a high-critical-temperature (T/sub c/) oxide superconducting material. New models of bearings with a free rotation axis were assembled. In these models, the superconductor, YBa/sub 2/Cu/sub 3/O/sub x/, prepared by the quench and melt growth (QMG) method, was applied to the bearing section and a permanent magnet was used for a rotor. This development originated from the knowledge that YBa/sub 2/Cu/sub 3/O/sub x/ prepared by the QMG method has a stronger pinning force for magnetic flux than that of conventional superconductors. A study of the forces and the damping for magnet rotation above the QMG superconductor was also made. It showed that levitation force and lateral force due to flux pinning were extremely large and damping for magnet rotation was small.         Measurement of repulsive force of high T/sub c/ materials due to Meissner effect and its two dimensional distribution    H. Ishigaki, M. Itoh, M. Hida, H. Endo, T. Oya, T. Ohyama and T. Minemoto Summary: As a basic study for magnetic bearings using high-T/sub c/. superconductors, evaluations of the materials were conducted. These evaluations included measurements of the repulsive force and lateral restoring force of various kinds of YBCO pellets. Pure air, which was supplied in the process of fabrication, and the presence of Ag in YBCO showed evidence of the effects of increasing the repulsive force. The lateral restoring force which was observed in the lateral displacement of a levitated permanent magnet over YBCO pellets was also affected by pure air and the presence of Ag. A new measuring instrument for magnetic fields was developed by using a highly sensitive force sensor. Because this instrument has the capability of measuring the repulsive force due to the Meissner effect, it was used for evaluating the two-dimensional distribution of superconducting properties. Results show that the pellets had nonuniform superconducting properties. The two-dimensional distribution of residual flux density on the pellets which had been cooled in a magnetic field (field cooling) was also observed by means of the instrument. The mechanism for generating lateral force is discussed in relation to the distribution.         Analysis of high-performance counter-type A/D converters using RSFQ logic/memory elements    S.V. Rylov Summary: A new family of counter-type Josephson-junction A/D converters using ultrafast rapid single-flux quantum (RSFQ) logic/memory elements is proposed. The converters are built in two main blocks: a low-bit differential-code A/D converter running with subterahertz clock speed and a RSFQ-logic-based digital processing unit providing digital low-pass filtering and sample rate reduction. It is shown that such converters can be treated as digital SQUIDs possessing an extremely high slew rate (up to 10/sup 11/ phi /sub 0//s) combined with flux resolution close to that of analog DC SQUIDs (up to 10/sup -6/ phi /sub 0/Hz/sup -1/2/). Several ways of implementing both main blocks to make it possible to tradeoff these parameters against converter complexity are presented and discussed.         New elements of the RSFQ logic family    O.A. Mukhanov, S.V. Polonsky and V.K. Semenov Summary: In this report, new rapid single-flux quantum (RSFQ) elements (OR-AND, NOR-AND, half adder, multiplexer, demultiplexer, and shift registers) are presented. Operation of these gates has been studied with the help of the personal superconductor circuit analyzer (PSCAN) within the standard RSJ model of Josephson junctions. Parameter margins and other performance limits of the new elements are thoroughly investigated.         Noise in relaxation-oscillation-driven DC SQUIDs    S.A. Gugoshnikov, O.V. Kaplunenko, Yu.V. Maslennikov and O.V. Snigirev Summary: The noise properties of the simple relaxation-oscillation-driven DC SQUIDs (RO-SQUIDs) have been studied. A limitation of its internal energy sensitivity E/sub v/ at a level close to 4*10/sup -31/ J/Hz due to the influence of the Josephson junction plasma oscillation has been found for the 5- mu m-design-rule technology. The signal characteristics with the transfer flux-to-voltage factor up to 2 mV/ Phi /sub 0/ and equivalent noise flux of about 1.3*10/sup -6/ Phi /sub 0//Hz/sup 1/2/ in the new all-niobium version of the balanced RO-SQUID have been measured.         Properties of the YBCO thin film interferometers fabricated on ZrO/sub 2/ bicrystal substrates    A.S. Kovalev, S.I. Krasnosvobotsev, M.Yu. Kuprijanov, A.G. Maresov, A.A. Ozerenko, E.V. Pechen, V.G. Pirogov, I.S. Pogosova, O.V. Snigirev and I.I. Vengrus Summary: The properties of DC SQUIDs made of YBCO thin film deposited on ZrO/sub 2/ bicrystal substrate and the nature of the fabricated Josephson junctions have been studied. It is found that the characteristics of the junctions are similar to those of the SNS structures with paramagnetic impurities in the N layer. A level of interferometer noise close to 5*10/sup -4/ Phi /sub 0//Hz/sup 1/2/ and a magnetic field sensitivity of 10/sup -10/ T/Hz/sup 1/2/ at frequencies higher than 25 Hz in the usual feedback mode of the SQUID operation have been achieved at 77 K.         Interferometric, holographic techniques for Y-Ba-Cu-O film patterning    A.A. Blyablin, V.A. Feoktistov, A.S. Kovalev, V.V. Korneev, V.N. Okhrimenko, A.M. Popov, B.V. Seleznev and O.V. Snigirev Summary: A laser single-pulse heating process was developed for the reversible patterning of YBCO thin films. The lattice, which consists of superconducting and nonsuperconducting lines, was fabricated in an area of 4*4 mm/sup 2/. The period of the lattice depended on the optical scheme and ranged between 1.5 and 40 mu m. A 1.06- mu m YAG laser, which provided 0.2-0.3 J /cm/sup 2/ power density at the film surface with a pulse duration of 10-15 ns and a coherence length close to 15 cm, was used for the patterning in the usual interferometric scheme with split beams. The result suggests that such a process, which utilizes holographic masks, can be a powerful technique for high-T/sub c/ thin-film device fabrication.         Direct measurements of the magnetic field induced by optically polarized /sup 3/He atoms    S.A. Gudoshnikov, A.N. Kozlov, Yu.V. Maslennikov, A.Y. Serebrjakov and O.V. Snigirev Summary: An alternative magnetic field induced by the standard cell of an optically pumped /sup 3/He magnetometer has been directly measured by the SQUID-based second-order gradiometer with a signal-to-noise ratio higher than six. A measured field of 5*10/sup -13/ T at a 5-cm distance from the cell axis and a transverse relaxation time of 7 min have been found. The measured transverse decay time was equal to 7 min; thus, the resolution in the frequency domain is limited at a level on the order of 10/sup -3/ Hz, which corresponds to an uncertainty of approximately 5*10/sup -11/ T. The results imply that the direct measurement of the induced field in the optically pumped /sup 3/He magnetometers makes it possible to introduce a suitable metrological scale in the region of the weak magnetic field 5*10/sup -8 /T         Sensitivity of the balanced Josephson-junction comparator    T.V. Filippov and V.K. Kornev Summary: The sensitivity of a balanced comparator composed of two overdamped Josephson junctions fed by single flux pulses is calculated, taking into account both thermal and quantum fluctuations. The results of the analysis are compared with those of recent experiments. Ultimate resolution of the balanced comparator with feasible junction parameters is estimated to be as high as approximately 50 pA/Hz/sup 1/2/ at 4 K and approximately 10 pA/Hz/sup 1/2/ at T to 0 K. Performance limits of the device are compared with those of its single-junction counterpart.         Detecting properties of YBaCuO thin film bridges    A.N. Tavkhelidze, L.S. Kuzmin, E.S. Soldatov, V.N. Okhrimenco, A.S. Kovalev, B.V. Seleznev and V.G. Pirogov Summary: A study is made of the properties of YBaCuO superconducting microbridges. They were fabricated by both direct photolithographic techniques and focused laser beam patterning. The YBaCuO thin films were deposited onto ZrO/sub 2/, MgO, and SrTiO/sub 3/ substrates by laser ablation of a massive YBaCuO target. The Josephson effect was observed in the bridges by detecting Shapiro steps and selective responses under irradiation with a signal frequency of 27-36 GHz. The value of the product I/sub c/R/sub N/ reached 4.5 MV at T=4.2 K and 420 mu V at T=77 K. The best values for wideband sensitivity eta (T) and noise-equivalent power NEP(T) were eta (77)=5*10/sup 3/ V/W NEP(77)=2*10/sup -12/ W/Hz/sup 1/2/ eta (20)=2.5*10/sup 6/ V/W, and NEP(20)=10/sup -14/ W/Hz/sup 1/2/. The estimation of noise by the width of the selective response shows than the internal noise is 1.5-2.5 times higher than the thermal value.         Towards the quantitative theory of the high-T/sub c/ Josephson junctions    M.Yu. Kupriyanov and K.K. Likharev Summary: The possible reasons leading to the reduction of the characteristic voltage V/sub C/ of the high-temperature-superconductor (HTS) Josephson Junctions are discussed. It is emphasized that the electron scattering at the superconductor-normal-metal (SN) boundaries plays a decisive role in HTS weak links. Rough estimates of the parameter gamma /sub B/ describing the SN boundary transparency were obtained. Calculations of the properties of the SNS sandwiches, variable thickness bridges, and SNIS' tunnel junctions within the framework of BCS-based theories of the Josephson effect have been carried out using models which take into account the low transparency of HTS/N-metal interfaces, and possible values of their I/sub c/R/sub N/ product are estimated.         Experimental implementation of analog-to-digital converter based on the reversible ripple counter    L.V. Filippenko, V.K. Kaplunenko, M.I. Khabipov, V.P. Koshelets, K.K. Likharev, O.A. Mukhanov, S.V. Rylov, V.K. Semenov and A.N. Vystavkin Summary: A new A/D converter which includes a comparator, and a reversible binary counter with DC outputs has been designed, fabricated, and tested. The comparator generates two trains of the single-flux-quantum (SFQ) pulses in response to increasing or decreasing input signal. The pulses are transferred through SFQ transmission lines to the adding and diminishing inputs of a reversible counter. The reversible counter has been realized by supplementing the usual counter with the SFQ transmission lines, splitters; and confluence elements for sending diminished pulses directly to each bit. Nondestructive read-out of the counter contents is carried out by SFQ/DC converters connected to each counter bit. The integrated circuit is fabricated using 5- mu m Nb-AlO/sub x/-Nb Josephson junction technology with a critical current density about 500 A/cm/sup 2/. External Mo shunts of the junctions provide the value of beta /sub c/         A MM-wave radiometer with planar Nb/a-Si/Nb Josephson junction    V.A. Kulikov, L.V. Matveets, A.L. Gudkov, V.N. Laptev and V.I. Makhov Summary: A report is presented on an investigation of the electrical and detection properties of thin-film step-edge submicron Nb/a-Si/Nb Josephson junctions for use as a detector in radioastronomical radiometers. These junctions are stable, thermally recyclable junctions with nonhysteretic I-V characteristics, R/sub n/=(20-200) Omega and j/sub c/ approximately 10/sup 5/ A/cm. A wideband modulation radiometer for the 4-mm-wavelength range with a Nb/a-Si/Nb Josephson junction has been developed. The best fluctuation sensitivity has been achieved at 0.007 K for a 1-s. integration time.         Superconductivity in YBa/sub 2/Cu/sub 3/O/sub 7//PrBa/sub 2/Cu/sub 3/O/sub 7/ superlattices    Q. Li, X.X. Xi, X.D. Wu, A. Inam, S. Vadlamannati, R. Ramesh, S. Schwartz, D.M. Hwang, B. Wilkens, J.A. Martinez, W.L. McLean and T. Venkatesan Summary: High-quality YBa/sub 2/Cu/sub 3/O/sub 7//PrBa/sub 2/Cu/sub 3/O/sub 7/ superlattices with desired thicknesses of each component were fabricated by laser deposition. Superconductivity was studied by varying both YBa/sub 2/Cu/sub 3/O/sub 7/ and PrBa/sub 2/Cu/sub 3/O/sub 7/ layer thicknesses. The results indicate that an isolated single unit cell YBa/sub 2/Cu/sub 3/O/sub 7/ layer (nominal thickness of 12 AA) is superconducting. The increase of T/sub c/ from the lower value of a single unit cell layer to 90 K in thick films and the enhancement of T/sub c/ for a given thickness of YBa/sub 2/Cu/sub 3/O/sub 7/ when the PrBa/sub 2/Cu/sub 3/O/sub 7/ layers decreased to less than approximately 30 AA could be attributed to the interlayer coupling effect. Superconducting transitions of superlattices in an applied magnetic field were studied. The interlayer coupling effect on vortices can be seen by comparing the transition curves in high magnetic fields of thick film, ultrathin film, and superlattice. For the samples with very thin YBa/sub 2/Cu/sub 3/O/sub 7/ layers, similar results to vortex-antivortex pair phase transition were observed by measuring the temperature dependence of resistance, magnetoresistance, and I-V curves, indicating strong two-dimensional behavior in very thin YBa/sub 2/Cu/sub 3/O/sub 7/ films.         A system for quench detection in the superconducting field winding of a synchronous generator    W. Engl, H. Lorenzen and W. Rehm Summary: In order to protect the superconducting field winding of a model synchronous generator against thermal destruction during a quench, the voltage differentials between two parts of the field winding are measured. In practice this method of quench detection is not good enough, as contrary to theory, normal dynamic operation in itself causes significant voltage differentials. The behavior of electrical transmissions within the excited field and armature circuits producing voltage differentials are identified. A process computer is used to simulate these voltage differentials in real time. It is also necessary to use an observer to compensate for the time drift which occurs between the real winding behavior and the digital parallel model. Only significant deviations between measured and simulated signals indicate a quench and release an emergency shutdown of the generator.         Influence of converters on the superconducting field-circuit of a three-phase synchronous generator    H. Groter, H. Lorenzen, W. Rehm and R. Schweiger Summary: Experimental investigations of the influence of converter feeding the field circuit of a three-phase synchronous generator with a superconducting field winding have been performed. Four converter circuits have been tested: a B6 three-phase bridge, two parallel B6 three-phase bridges, a three-phase bridge with bypass thyristors, and a high-current power-MOSFET converter. Steady-state and transient operation have been tested. There was a special interest in the harmonics generated by the converter circuits and their power dissipation in the low-temperature region. The thermal reaction of the field circuit has also been considered. A method has been developed to prevent the superconducting winding from the quenching in transient operation.         Design analysis of a novel low temperature bolometer    M. Nahum and P.L. Richards Summary: The authors propose a novel antenna-coupled superconducting bolometer which makes use of the thermal boundary resistance available at low temperatures. The radiation is collected by a planar self-complementary antenna and thermalized in a small thin-film resistor. The resulting temperature rise is detected by a transition edge thermometer which can be (but need not be) a separate film. All components are deposited directly on substrate so that arrays can be conveniently produced by conventional lithographic techniques. The active area of the bolometer is thermally decoupled by its small size and by the thermal resistance of the boundaries with the substrate and the antenna terminals. Design calculations based on a 2- mu m*2- mu m film of a superconductor with T/sub c/ approximately=0.1 K give an NEP approximately=10/sup -18/ WHz/sup -1/2/, a time constant approximately=10/sup -6/ s, and responsivities up to approximately=10/sup 9/ V/W. These specifications meet the requirements for NASA's Space Infrared Telescope Facility and Sub-Millimeter Moderate Mission. Useful applications also exist at /sup 3/He and /sup 4/He temperatures. The calculated NEP scales as T/sup 5/2/. Materials, architectures, and readout schemes are discussed.         DC-SQUID electronics based on adaptive positive feedback: experiments    H. Seppa, A. Ahonen, J. Knuutila, J. Simola and V. Volkman Summary: It is shown that DC-SQUID read-out electronics can be realized utilizing positive feedback without deteriorating the SQUID noise performance. The required gain rise is achieved by interconnecting the SQUID output and a flux modulation coil via a cooled FET acting as a voltage-controlled resistor; different SQUIDs with different types of FETs have been studied experimentally. Possible ways of adaptively controlling the feedback gain produced by the positive feedback are briefly discussed.         Minimisation of coupling losses in multiwire superconducting cables    V.E. Sytnikov Summary: The effect of the construction parameters of a multiwire cable on its operational characteristics is discussed. It is shown that when the number of wires is changed, a minimum occurs on the curve of the total coupling losses versus number of wires (total cross section is constant). The minimum position depends, in general, on the total cross section of the cable and the ratio between the transverse resistances of wire and cable. Calculation formulae for defining optimization construction are presented.         Study on transverse resistance and coupling losses in superconducting cables    V.E. Sytnikov, G.G. Svalov, I.P. Radchenko and A.V. Zlobin Summary: Superconducting transposed cables with different transverse resistivities have been investigated. These cables consist of NbTi-Cu wires with different coatings. The magnitude of interwire resistance has been varied from 10/sup -3/ up to 10/sup -7/ Omega . The methods and results of measuring the transverse resistance and its dependence upon compression and external magnetic field are discussed. On the basis of the results obtained, the construction of the cables with the anisotropic transverse resistance providing a high stability level is proposed. The coupling losses in the cables with different transverse resistances have been measured. The proposed construction of the cables should provide reduction of coupling losses by a factor of 10/sup 2/-10/sup 3/ as compared with soldered cables.         Inductive method for AC and DC testing, creation and testing of installations    P.I. Dolgosheev, V.E. Sytnikov, K.P. Radchenko and N.A. Vahtinski Summary: High values of critical current multiwire superconducting cables make it impossible to use the galvanic current input method for sample testing. This necessitates the development of an inductive method. The main advantage of this method is the relatively low cost of generating very high currents. Series of toroidal and solenoidal transformers has been developed and tested. The transformers with a steel core have been used for DC tests, and those without the steel core have been used for DC and AC tests. Currents of up to 126.3 kA (quench current DC) and 50 kA AC have been obtained. Joint resistance has been less than 10/sup -10/ Omega . The possibility of using the inductive method for the critical, quench, and recovery currents is discussed, and results obtained are presented.         Concentric superconducting shells with weak links in an external magnetic field    J. Pirnat and Z. Trontelj Summary: A model calculation for a system of concentric superconducting shells with one weak link in each shell is considered to help understand the behavior of granular high-temperature superconductors. In this type of superconducting material the contacts between grains often resemble the weak links in classical superconductors. The behavior of a system of concentric superconducting shells, containing weak links, in an external magnetic field is studied. The dependence of inner magnetic flux on external magnetic flux is calculated, as well as the distribution of magnetic field in the space between the shells. An additional modulation appears in the phi /sub i/ vs. phi /sub ex/ curve. The modulation period depends on the spacing between the shells but not on the number of shells. The cooperative behavior of the system of shells is considered as well.         Microwave detection with high T/sub c/ superconducting thin films    I. Zaquine, J.C. Mage, B. Marcilhac and D. Dieumegard Summary: Measurements were made of the microwave responses of YBaCuO superconducting thin films. The sample was a chemically etched line approximately 200 mu m long and 20 mu m wide. The measurements were performed in three different frequency ranges: 1-40 GHz, 90-100 GHz, and HeNe laser. Different kinds of responses were observed: a bolometric peak that can be easily related to dR/dt and a nonbolometric peak. The power dependence of the response was plotted for different bias currents. The response time was shorter than 1 mu s in most cases. The sensitivity was not comparable to that of semiconductor detectors, but it is shown how the design of this detector could be optimized to improve its sensitivity. The operating frequency range is superior to that of other detectors. A review of the different models regarding the response of superconducting thin films to photon irradiation is presented, and the experimental results are interpreted.         Processing parameters and kinetics of bromination and chlorination in the YBa/sub 2/Cu/sub 3/O/sub 6+x/ system    H.B. Radousky, R.S. Glass, D. Back, A.H. Chin, M.J. Fluss, J.Z. Liu, W.D. Mosly, P. Klavins and R.N. Shelton Summary: The introduction of halogens such as Cl/sub 2/ and Br/sub 2/ can restore 90 K superconductivity to oxygen deficient YBa/sub 2/Cu/sub 3/O/sub 6+x/. This is potentially important for applications to thin-film devices due to the low processing temperatures required relative to reprocessing with oxygen. Low-temperature (260 degrees C) and short-time (>5 min) bromination has been shown to convert initially insulating YBa/sub 2/Cu/sub 3/O/sub 6.2/ powder to a high-temperature superconductor with properties similar to the standard O/sub 7/ material. This process has now been extended to single crystals as well, but with somewhat different processing parameters. Thermal gravimetric analysis (TGA) coupled with mass spectrometry indicated that the Br becomes strongly bonded with no release of Br observed in taking powder samples to 1000 degrees C in flowing forming gas (2%H/sub 2//98%N/sub 2/). The reaction has also been found to be highly exothermic for both Br and Cl treatments, which is consistent with the strong bonding of the bromine.         On the reduction of flux creep in superconducting accelerator magnets    K. Kwasnitza and C. Widmer Summary: The authors have performed intensive studies on flux creep in high-T/sub c/ superconductors and on M transition curves inside the hysteresis area and were able to reduce dM/d ln t at a given B by an order of magnitude by appropriate previous magnetic field cycling. The reduction can be explained by the critical state model. As this model applies both to the high-T/sub c/ and to technical 4-K superconductors, the authors' dM/d ln t reduction method can be applied also to NbTi or Nb/sub 3/Sn superconductors for accelerator magnets.         The study of structure and properties of Nb/sub 3/Sn layers in multifilamentary superconductors manufactured by the internal tin method    V.I. Panzyrny, A.K. Shikov, I.I. Davydov, N.A. Belyakov, A.D. Nikulin, I.I. Potapenko, A.V. Parno, V.D. Zheleznyakov, V.S. Kruglov, T.A. Davlatyan and S.I. Novikov Summary: The processes of diffusion interaction of niobium filaments and a copper matrix in conductors manufactured by the internal tin method were investigated. The aim was to determine the effect of heat treatment modes on the structure and properties of a Nb/sub 3/Sn layer being formed in conductors with the centrally positioned Sn alloy. It was established that as a result of the doping of the matrix and filament materials, the overall critical current density (without taking into account the stabilizing copper) reaches into 5.12*10/sup 4/ A/cm/sup 2/ in a 16-T field and 2.08*10/sup 4/ A/cm/sup 2/ in a 18-T field.         In situ preparation of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ thin films deposited by ion beam sputtering: preliminary results    S. Barbanera, F. Murtas, L. Scopa, V. Boffa, G. Paterno, A. Montone and M.V. Antisari Summary: Thin films of the high-temperature superconductor Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ have been grown in situ by ion beam sputtering from metal binary alloys. The metal binary alloys used were YCu and BaCu. The correct composition of the deposited film was obtained by adjusting the position of the targets with respect to the ion beam. The films were deposited onto heated SrTiO/sub 3/ substrates in oxygen partial pressure. After deposition the samples were slowly cooled to room temperature with a short step at 450 degrees C. The films did not need any further annealing after deposition and showed superconducting properties.         Author Index (1990 - Part 2)    No author information available Summary: Not available

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