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1972     Front Cover (1972)    No author information available Summary: Not available         Table of Contents (1972)    No author information available Summary: Not available         Conference Information (1972)    No author information available Summary: Not available         Status of Superconducting Machines at IRD Spring 1972    A.D. Appleton Summary: This paper relates to the development of superconducting machines at International Research & Development Co. Ltd., since 1963. The work has been carried out on behalf of the Ministry of Defence (Navy), the National Research Development Corporation and C.A. Parsons & Co. Ltd. In 1966 a 50 hp model superconducting homopolar motor was commissioned, and in 1971 full load tests were performed on a 3250 hp motor (the Fawley motor). At the present time IRD is engaged upon the construction of two superconducting d.c. machines, one motor and one generator, for a marine propulsion system which will undergo sea trials in 1973. In addition to the above, IRD has been engaged upon the development of superconducting a.c. generators since 1968. The major theme of this paper is to show that there are crucial aspects of superconducting d.c. machines which determine the nature of a development programme; these are discussed together with some equally important but less critical aspects. Discussions on the marine propulsion system and the Fawley motor are included and a brief mention is made of superconducting a.c. generators, although the latter is the subject of another paper at this conference.         Superconductive Naval Propulsion Systems    W.J. Levedahl Summary: Virtually all stationary power for military, industrial or domestic applications is produced in central power stations and transmitted electrically to multiple users. Optimum location of power plants and the ability of different users to tap the energy stream at diverse points have contributed greatly to the efficiency of both civilian and military economies. This flexibility is seldom available to aircraft, ships and land vehicles because of the size and weight of conventional electric motors and generators. Diesel-electric locomotives, which require extreme operating flexibility, are the primary current examples of mobile electric propulsion.         Superconductive Ship Propulsion Systems    G.R. Fox and B.D. Hatch Summary: Electrical ship propulsion systems are a particularly attractive area for applying superconductivity. The many advantages of electrical ship propulsion systems can be obtained, and the increased power density and economies possible with superconductive machines permit an even greater flexibility in new ship designs. Both dc and ac propulsion systems are possible and hybrid systems (ac generator and dc motor) may also be considered. Experiments have demonstrated the operation of two superconductive dc generators and have also provided new information for the design of liquid metal current collectors for large currents in high intensity fields. The refrigeration cycles that may be employed to provide continuous cryogenic cooling are presented. In particular, components for a turbo refrigerator for long life and high reliability are discussed, and the characteristics of the turbo refrigerator are described.         An Airborne AC Superconducting Generator    L.R. Lowry Summary: An ac generator utilizing a rotating superconducting field is described. The generator will produce 1000 kVA at 5000 volts, 3 phase, 400 Hzwith a short time overload capability of 5000 kVA. Predicted performance, size, and weight of the superconducting generator are compared with that of a machine of similar rating using conventional airborne generator technology. It is concluded that superconducting generators will exhibit significant weight reductions for generators rated above 2 MW.         Superconducting Considerations In Rotating Electrical Machines    Z.J.J. Stekly Summary: This paper deals with the problems associated with superconducting field windings. The basic requirements for the field are discussed in terms of size, magnetic energy stored, power level, speed of rotation, number of poles. While the field winding is basically dc in nature, it is exposed to time varying magnetic fields and forces due to the armature currents generated by loading transients, faults, unbalanced electrical loads, as well as load generated harmonics. The effect of these on the design of the field as well as on the performance of the superconductor is discussed.         The Role of Superconducting Magnets in Tracked Magnetic Cushion Vehicles for High Speed Transportation    J.R. Reitz Summary: Magnetic levitation as a suspension mechanism for high speed vehicles is reviewed. Important parameters are magnetic lift per unit magnet weight, lift-to-drag ratio, and suspension height. The effect of vehicle-track clearance on ride quality is discussed, and the advantages of a large clearance are demonstrated. Superconducting magnets, because of their high-fieldstrength per unit weight, are particularly suited to this application. Specific problems resulting from the use of superconducting magnets are discussed.         Magnetic Levitation of High Speed Ground Vehicles    H.T. Coffey, F. Chilton and L.O. Hoppie Summary: Two nonsuperconducting and four superconducting magnetic levitation systems were studied to determine the technical feasibility of levitating a l00,000-lb vehicle. Each of these systems was found to be technically feasible but each had widely varying characteristics that made a definitive choice between them impossible without additional information. The system using superconducting magnets on the vehicle and a conducting sheet guideway appeared to us to be the best choice based on the information available, and the characteristics of this system were studied in detail. The cryogenic requirements and the design of a completely stabilized superconducting magnet were emphasized and were found to be technically feasible and quite reasonable.         The Magneplane: Guided Electromagnetic Flight    H.H. Kolm and R.D. Thornton Summary: A cylindrical vehicle equipped with superconducting coils is suspended resiliently by eddy current repulsion one foot above a cylindrical, trough-shaped aluminum guideway surrounding the lower third of the vehicle's circumference. The vehicle is free to roll so as to assume the correct bank angle in curves. It is propelled by a travelling magnetic field generated by current loops which form an integral part of the guideway. This field is synchronized by wayside control units on the basis of information transmitted from the vehicle; it reacts against the superconducting vehicle coils to provide synchronous acceleration, deceleration or cruise, and also generates vertical and lateral forces to apply active damping to oscillations in the heave, sway, pitch, yaw and roll modes. Lift-to-drag ratio is about 20 at 250 mph, propulsion efficiency is about 80%, and guideway loading is about 2 psi.         The Conceptual Design of a 750-ton Hydrofoil Utilizing a Superconducting Main Propulsion System    S.T.W. Liang and L.F. Martin Summary: The conceptual design of a 750-ton hydrofoil utilizing a superconducting main propulsion system is described. This is a fully integrated design concept in which the superconducting machinery is introduced into the shin system design at its very inception. The critical areas evaluated are ship configuration, performance, propulsion system, propulsor, and auxiliary systems. The study results show that use of a sunerconducting power system for propelling a large hydrofoil has many advantages: greater endurance, lighter weight, and more flexible arrangement.         Flooded Rotor, Direct Current Acyclic Motor, with Superconducting Field Winding    J.P. Chabrerie, G. Fournet and A. Mailfert Summary: Several studies performed since 1966 by the LGEP and LCIE have lead to the development of a 60 kW flooded rotor homopolar motor operating at low speed (600 r/min). This machine uses multiple discs and superconducting field winding. After a short description of the model motor, and a brief account of the main test results, some problems due to the coexistence of a high magnetic field, non ferromagnetic materials, and liquid metal, are examined. The overpressure phenomena due to the rotation of the lateral liquid rings, as well as the electromagnetic devices installed in order to suppress this inconvenience are discussed. The paper concludes with some comments on the choice of liquid metals and their applications to more powerful machines.         Superconducting Magnetic Energy Storage and Transfer    H.L. Laquer, J.D.G. Lindsay, E.M. Little and D.M. Weldon Summary: Energy storage and transfer experiments from superconducting coil into resistive loads are described. Energy transfer is achieved with a normal going superconducting switch. Voltage and circuit conditions for full normalization of the switch are discussed. Maximum energies transferred to date have been 10 kJ at 800 A and 1000 V.         Model Coil Test Results for a Pulsed Superconducting Magnet Energy Storage System    E.J. Lucas, W.F.B. Punchard, R.J. Thome, R.L. Verga and J.M. Turner Summary: A review is given of the design specifications for a 100,000 Joule system and the test results obtained on two model coils having energy storage capabilities of 500 Joules each. The energy storage coils that are being considered must be charged in a fraction of a second and discharged in a fraction of a millisecond. The losses are calculated on two models. Both assume that the coil remains superconducting during the charge period. However, on discharge one model assumes that the coil goes normal and one that it remains superconducting. In both models the losses during the charge period are considered to be the superconductor magnetization losses and eddy current losses in the normal substrate. During discharge on the former model, the current is considered to flow entirely in the resistive substrate and the losses are considered to be made up of transport and eddy current losses in the normal substrate. On the latter model, the losses are considered to be a magnetization loss in the superconductor and eddy current losses in the normal substrate. Data will be given on two model coils wound with 48 strand braided conductors. Each of the strands in the first coil has 121 filaments of NbTi and each strand in the second coil has a single NbTi filament.         Proposed Propulsion System for Magnetically Levitated Guided Ground Transportation    D.L. Atherton Summary: A propulsion system, using a controlled variable-speed linear synchronous motor, is proposed for magnetically levitated guided ground transportation systems. The motor may be integrated with the magnetic levitation system which will use superconducting magnets for high speed systems. The motor concepts are described together with its local, remote or preset control features and inputs. The motor can be self starting and regenerative braking is possible. System control, safety aspects and a mechanical analogue are discussed for the magnetic levitation application. It is concluded. that the attractive control features and low speed starting performance may more than offset the increased cost of the semiconductor power switching circuits which are required.         Electromagnetic Lift and Drag Forceson a Superconducting Magnet Propelled Along a Guideway Composed of Metallic Loops    L.O. Hoppie, F. Chilton, H.T. Coffey and R.C. Singleton Summary: An exact solution to the problem of a single constant current magnet (or group of magnets) moving uniformly along a guideway of metalic loops has been obtained and programmed for computerized results: single layer, double layer, or ladder tracks can be analyzed. The actual current in the loops as well as the actual lift and drag forces are obtained.         Integrated Systems for Magnetic Suspension and Propulsion of Vehicles    G. Danby and J. Powell Summary: Integrated magnetic suspension and propulsion system characteristics are discussed. It is concluded that repulsive suspension with linear synchronous motor drive are the most promising. In addition, preliminary results are given for a novel suspension concept which appears to provide strong lifting and restoring forces, large clearance and low drag.         Three-Phase-Synchronous Alternator with Superconducting Field Winding    D. Eckert, F. Lange, M. Endig, G. Muller and W. Seidel Summary: The superconducting field winding is a quadrupole magnet partially stabilized, having a field gradient of 55 Tesla/m and is assembled vertically. The armature is constructed as a cup with the cryostat in its inner space and rotating at 1500 rpm. The measured maximum power was 21 kVA. There is no iron in the alternator. In spite of the mechanical forces and the 200 A-leads the helium losses amounted to 15 l/min (gaseous) only at fullpower. The alternator was successfully tested working on a passive network. With two phases only the helium losses amounted to 21 l/min. Working synchronized and directly connected to the municipal power supply system was successful, too. By sudden changes of the load or shortcircuiting the armature at reduced power no disturbances of the superconducting magnet were observed. The field winding could be switched on and off without quenching (time constant: 2 seconds).         A Review of the Critical Aspects of Superconducting A.C. Generators    A.D. Appleton and A.F. Anderson Summary: This paper reviews the development of superconducting generators undertaken by IRD on behalf C.A. Parsons and Company Ltd. An outline drawing of a machine concept is presented with a discussion of the more critical development problems. An account is given of the manner in which performance is influenced by machine geometry, in particular by inter-winding coupling factors on substransient reactance. The principal mechanisms causing machine losses are reviewed and the techniques used for their prediction and minimisation are outlined.         MIT - EEI Program on Large Superconducting Synchronous Machines    J.L. Smith Jr., J.L. Kirtley Jr., P. Thullen and H.H. Woodson Summary: This paper is a progress report on the program to demonstrate the feasibility and potentials for the application of superconductors in the rotating field windings of large central-station synchronous generators. A brief history of the program and a synopsis of previously reported results are given. The second experimental machine (approximately 2 MVA) is described and progress on its construction and testing is given.         Superconductor Synchronous Generators    C.J. Mole, H.E. Haller III and D.C. Litz Summary: This paper reviews the fundamental characteristics and operating modes of superconducting synchronous generators for several applications. The applications of these machines will be discussed, together with auxiliary equipment such as the refrigeration and cryogenics systems.         The Pressing Need for Better and Less Expensive Underground Transmission    A.F. Corry Summary: Future transmission systems will handle larger blocks of electric power and a greater percentage will be installed underground. Capabilities and costs of current systems are presented and installed cost goals are discussed. The importance of continued effort in this field is stressed.         The Place of Cryogenic Systems in More Economical Underground Power Transmission    J. Nicol Summary: lt is widely believed that there will be greatly increased use of underground power transmission systems during the coming decades. There will be two principal reasons: The need to provide much more electrical power in city centers where overhead rights-of-way are not available, and the public's objection to the proliferation of overhead EHV and UHV transmission lines in suburban and rural areas. underground         Research and Development of Superconduction Cables for High Power Transmission.    P. Dubois, I. Eyraud and E. Carbonell Summary: This paper reviews work done on cryocables by Compagnie Gonerale d'Electricite and Air Liquide : design of several types of DC and. AC superconducting cables ; measurements on powders for thermal insulation ; measurements of the dielectric properties of vacuum and solids in helium ; measurements on cable samples ; construction and testing of a full scale model of pipes and thermal shields.         Mechanical Design of Tubular Conductors for A.C. Superconducting Power Transmission    J.A. Baylis Summary: The major mechanical problems in the design of tubular conductors for superconducting cables are the thermal contraction and the electromagnetic forces which act during fault currents, The majority of this paper is concerned with thermal contraction,and various methods of dealing with it are analysed and discussed. Special /spl Omega/ bends in the conductor route seem the best solution. The electromagnetic forces are shown to fix the permissible tolerance on conductor straightness, and to determine the maximum distance between conductor supports.         AC Superconducting Power Transmission    R.W. Meyerhoff Summary: At the present time it is predicted that the electric utilities will need to double their capacity every ten years. The availability of low cost and efficient means for the underground transmission of large blocks of power may be one of the most significant factors which will determine the ability of the electric power industry to meet these rapidly growing demands. It is generally agreed however, that the present technology of underground power transmission is not capable of meeting the anticipated requirements and a new technique for transporting large blocks of power underground is needed.         Factors Influencing the Choice of Superconductor in AC Power Transmission Applications    E.B. Forsyth, M. Garber, J.E. Jensen, G.H. Morgan, R.B. Britton, J.R. Powell, J.P. Blewett, D.H. Gurinsky and J.M. Hendrie Summary: The last decade has seen both paper studies and model experiments in the laboratory on power transmission cables. Although a majority of workers studied niobium supported on rigid pipes, flexible cables of niobium, niobium-zirconium, and lead have been examined and recently conductors of niobium-tin have been proposed. In most of these studies the choice of conductor has been made on the basis of the hysteretic losses to be expected at the operating current. Some attention has been given to physical properties necessary for fabrication and su,bsequent satisfactory operation and to the cost of the materials. A recent study of superconducting power transmission cables carried out at Brookhaven National Laboratory for the National Science Foundation has shown that the choice of superconductor is profoundly influenced by overall system design decisions and the hysteretic losses are not an overriding factor. A more comprehensive list of influencing factors is shown below; the order does not indicate priority or relative importance         Large Composite Conductors for A.C. Superconductive Power Transmission    C. Graeme-Barber and B.J. Maddock Summary: Tubular niobium clad copper conductors with diameters up to 100 mm have been developed. Such sizes are equivalent to cable power ratings of a few GVA. Two production methods have been used: one based on extrusion, the other on forming the tube from a composite strip. Measurements on a sample of the 50 /spl mu/m niobium surface layer taken from one of the tubes indicate that the a.c. power losses of these conductors will be satisfactorily low. The most important development still required is the improvement of the overload current capacity.         The Development of Large Superconducting D.C. Magnets in Europe - Present and Future Applications    G. Bogner Summary: The state of development work is demonstrated by way of example of a number of magnet installations built for experiments in high-energy or plasma physics or which are shortly to be commissioned. The experience gained with large cylindrical magnets of fully stable NbTi-copper composite conductors have shown that such magnets can be manufactured on an industrial scale and that they can operate fully satisfactorily. This satisfactory operation is also expected of two magnet units with energy contents of 50 and 800MWs which are shortly to be commissioned. Remarkable successes have also been achieved with larger intrinsically or partially stable magnet systems with high cur rent densities, though setbacks have also been experienced in this area. Results obtained so far have led to the conclusion that intrinsically stable and twisted NbTi copper conductors with a copper-to-superconductor ratio of at least 2 :I should be used for such magnets and that themagnet winding packets-must be carefully fixed (impregnated) and reinforced. as well as adeqiately cooled.         Pulsed Superconducting Magnets    H. Brechna and M.A. Green Summary: The paper reviews the progress which has been made on pulsed superconducting magnets and a.c. composite conductors. It describes the performance of prototype pulsed dipoles. Future trends in the design of pulsed superconducting magnets are indicated.         Superconducting Magnet Requirements for Fusion Reactors    C.E. Taylor Summary: It would be perhaps premature to try to describe in detail the shape of future reactor magnets or to develop rules for their design. Rather, it would seem more useful to describe the several general approaches to fusion and the general size and shape of some examples of presently visualized reactor coils.         The NAL Bubble Chamber Magnet    J.R. Purcell and H. Desportes Summary: This paper describes the design of the superconducting magnet for the 30,000 liter NAL bubble chamber. The magnet has a winding bore of 14 ft. with a central field of 30 kG. Peak field on the conductor is 51 kG and the operating current is 5,000 amperes. The finished magnet with cryostat will weigh 140 tons with 88 tons of this as coils.         On Persistent Current Decay in a Superconducting Coil due to External Magnetic Field Oscillations    V.V. Andrianov, V.B. Zenkevich, V.V. Kurguzov, V.V. Sytchev and F.F. Ternovskii Summary: The use of superconducting magnetic systems for persistent current operation requiring no permanent connection to the supply source seems very attractive and, in a number of cases, the only feasible, for many an application of such systems. The majority of such applications are characterized by the presence of .outside disturbing factors causing magnetic field oscillations and, accordingly, oscillations of the current flowing in the magnet winding. A great importance is attributed in this case to the problem of whether the current in a shortcircuited magnet may decay with time under the effect of external magnetic field oscillations or, which is the same, whether these oscillations bring about the emergence of some effective resistance in the superconducting material of the magnet winding.         Current-Carrying Capacities of V/sub 3/Ga Superconducting Solenoids    S. Fukuda, Y. Tanaka and K. Tachikawa Summary: In this paper we report the current carrying capacities of V/sub 3/Ga tapes and wires in short samples and in pancakes or coiIs. Single pancakes were wound of tape of either 5-m or 100-m length-these lengths represent steps leading toward the production of the much longer pieces needed for the construction of magnets of practical size. Coils contained wire of 120-m length.         A Technique for Observing Magnet Normalcies    K.R. Efferson Summary: Various forms of superconducting liquid helium level detectors have been described in the past. The author's experiments with one of these has shown that its fast response time makes it useful for measuring fluctuations of the surface of a liquid helium bath. Liauid level fluctuations can be caused by such things as mechanical vibrations, thermoacoustic oscillations, boiling effects due to constant and nonconstant heat leaks, dewar pressure changes, and normal state transitions in superconducting magnets. Observation of changes in the liquid surface is particularly important in large superconducting magnet dewars where one needs as many clues as possible to indicate the status of the magnet and cryogenic system. This paper gives some information about the detector and level fluctuations in helium which may be useful to others         Superconducting Magnet for a Ku-Band Maser    R. Berwin, E. Wiebe and P. Dachel Summary: A superconducting magnet to provide a uniform magnetic field of up to 8000 G in a 1.14-cm gap for the 15.3-GHz (Ku-band)traveling wave maser is described. The magnet operates in a persistent mode in the vacuum environment of a closed-cycle helium refrigerator (4.5/spl deg/K). The features of a superconducting switch, which has both leads connected to 4.5/spl deg/K heat stations and there by does not receive heat generated by the magnet charging leads, are described.         Design Features of Superconducting Transport and Analysis Magnets    R.W. Fast and J.R. Heim Summary: The design features of a 2.0 kG/cm cold iron beam transport quadrupole and of a 18 kG, wide aperture particle analysis dipole are given. Operating currents of 250 and 350 amps, respectively, were chosen, corresponding to conductor current densities of 19.7 and 27.6 kA/cm/sup 2/. Coil construction provides good conductor cooling and supports the large electromagnetic forces. Rectangular cryostats to provide a large LHe volume above the coil have been used and have proven to be both inexpensive to construct and of low heat leak. A column support capable of reacting large loads to room temperature with negligible heat leak has been used.         The SLAC Two-Meter Diameter, 25-Kilogauss, Superconducting Solenoid,"UAMH BINN"    J.S. Alcorn, H.O. Petersen and S.J. St. Lorant Summary: A 2-meter bore, 25-kilogauss, superconducting solenoid is presently under construction at the Stanford Linear Accelerator Center (SLAC), which is a part of the Large Aperture Solenoid Spectrometer (LASS) facility, illustrated in Fig. 1. This solenoid, together with a liquid hydrogen target, wire spark chambers, scintillation and Cerenkov counters, a conventional 1 X 2-meter dipole magnet, and an IBM 1800 data-processing system, will be used initially for high resolution studies of meson and baryon production processes using RF separated r, K, and p beams in the 5- to 16-GeV energy region.         AC3 - A Prototype Superconducting Synchrotron Magnet    M.N. Wilson, R.B. Hopes, R.V . Stovold and G.E. Gallagher-Daggitt Summary: A pulsed superconducting dipole magnet has been built which fulfills many of the requirements of a synchrotron accelerator, It produces a field of /spl equiv/ 4T in a bore of 100 mm at a current of /spl equiv/ 5000 A and may be pulsed with a rise time of /spl equiv/ 1 second. The hysteresis loss per cycle is /spl equiv/ 50 joules.         Consequences of Replacing Conventional Magnets by Superconducting Magnets in an Existing Synchrotron    G. Bronca, G. Neyret, J. Parain and J. Perot Summary: In order to increase the energy of an existing synchrotron it is possible to replace conventional magnets by superconducting magnets operating at higher magnetic field. With niobium-titanium superconducting materials the sensible limit of the maximum field is 6 to 8 teslas. For the present CERN II synchrotron, a central field of 6 T will allow us to reach 1200 GeV, including straight sections to accommodate multipole correcting magnets. Main ring superconducting magnets with the same aperture as conventional magnets will allow us to use all existing equipment, such as the radio frequency system, the power supply and the control system. With these changes, a longer cycle duration is required; for the 1200 GeV svnchrotron a cycle of about 80 seconds has’been chosen.         Construction of a Superconducting Quadrupole Doublet: "O.G.A."    G. Bronca, J. Hamelin, J. Neel, J. Parain and M. Renard Summary: A quadrupole doublet of large angular acceptance was constructed during the last years at the Laboratory. The basic parameters of the two independant quadrupoles are a field gradient of 35 and 23 T/m in a useful diameter respectively of 20 and 30 cm and a magnetic length of 68 cm. The conductor using niobium-titanium material was made of twisted filaments each of 45 microns diameter. Experience achieved from the different states of construction will be reported with results of cryogenic and magnetic measurements made on the assembled quadrupoles. This doublet must be inserted in a secondary beam of the 3 GeV synchrotron to increase the production of charged pions. An expected gain of four has been considered in the project.         A Superconducting 8/spl deg/ Bending Magnet System    J. Allinger, G. Danby, B.D DeVito, R. Gibbs, D. Hsieh and J. Jackson Summary: A superconducting magnet system has been designed and is being constructed to bend the primary proton beam from the Alternating Gradient Synchrotron to the new North Experimental Area at Brookhaven National Laboratory by 8/spl deg/. The design of this system is based on extensive evaluation of materials involved and on detailed model studies. Details of the conductor and conductor tests, magnet circuit, magnet and cryostat construction and assembly, and refrigerator and transfer lines are given.         Prototype High Gradient Superconducting Quadrupole for Hyperon Focusing    B.P. Strauss and R.W. Oram Summary: This paper describes the construction of a prototype quadrupole magnet source 50 cm in length for use as a dc magnet for a proposed focused Cerenkov counter as well as possible use in an energy booster for the NAL synchrotror. It is of the "Super-ferric" type with cold iron laminations and tightly wound coils. It furthermore includes a new method for both reacting the magnetic forces and centering the coils.         The Design of a 16T Hybrid Magnet    P.E. Hanley Summary: The design of a magnet system consisting of a 2 inch bore 9.3T water-cooled magnet within the room temperature bore of a 6.7T superconducting solenoid is described. It is shown that this combination is the most effective way of extending a 2 MW high-field laboratory facility with regard to cost and reliability. The forces arising from an asymmetrical failure of the inner magnet and the method of containing them are discussed. It is shown that these forces can be minimised by using a water-cooled magnet consisting of concentric helices instead of the more usual Bitter form of construction. The cryostat for the outer magnet is described, and also the refrigeration system using a Philips PGH 105 cryogenerator. The superconducting magnet is to consist of discs wound from Nb-Ti multifilament superconductor stacked to form a solenoid. Adiabatic and cryostatic stabilisation are discussed,and it is shown that an optimum cooling channel width exists. Finally, the instrumentation for the operation of the hybrid magnet system is described.         Results of Tests on the Superconducting Part of a Hybrid Magnet    M.J. Leupold, Y. Iwasa and D.B. Montgomery Summary: In this paper we describe results of tests on a superconducting magnet which constitutes the outer coil of the hybrid magnet system presently under construction at the Francis Bitter NationaI Magnet Laboratory. The term "hybrid magnet" has been coined to describe one in which part of the field is generated by superconductors and part by non-superconductors. Such systems are able to produce higher fields than can be produced by superconductors alone. In addition, they can represent an economical approach to very high fields for laboratories which already posses a power supply or refrigerator.         Glass Reinforced Epoxy Structure for a Lightweight Superconducting Dipole Magnet    D.L. Atherton Summary: The mechanical structure for a 6.5 tesla, 33 cm winding bore, 102 cm magnetic length superconducting dipole magnet is presented. The saddle-coil magnet, which is intended for airborne magnetohydrodynamic power generators, is restricted to a total mass of 453.6 kg. Details of materials selection and testing are given. Magnetic stress analysis includes Lorentz, pinch and end repulsive forces. Structural design covers bending moments, tensile and shear stresses and deflections of the filament wound structure internal and external to the windings with emphasis on high stresses (10/sup 9/ N/m/sup 2/ tensile) and light weight. Jigs and development tests of sample structures are described 'and interlaminar shear is examined in detail. Fabrication is described. We show that the use of filament wound high strength glass-epoxy composite gives very high specific strength, considerable cost savings and is particularly well suited to the mechanical structures needed for large superconducting magnets.         Design and Model Tests for a 5 Tesla Superconducting Saddle Magnet    R.J. Thome and Z.J.J. Stekly Summary: A lightweight superconducting saddle magnet has been designed and is currently under construction. This paper presents a discussion of the magnet design and of model test results. The magnet is designed to be mounted in a dewar with a horizontal, 0.18 m diameter, room temperature bore. The design central flux density of 5 Wb/m/sup 2/ is uniform within 10% over an axial length of 0.88 m and to within 25% over a length of 0.98 m which is the distance between magnet end turns. The overall winding current density is 1.5 x 10/sup 8/ A/m/sup 2/ at an operating current of 485 A and the peak flux density at the windings is 7 Wb/m/sup 2/. System weight and size were reduced by utilizing titanium and high strength aluminum for the magnet support structure and by using an aluminum dewar with helium vapor cooled radiation shield. The magnet windings are conduction cooled with no internal cooling passages.         On the Performance of Nb/sub 3/Sn Test Coils for Levitated Multipoles, in L.He and in He Gas Up to 17 K    F. Rau, H.J. Jackel, A.P. Martinelli and S.L. Wipf Summary: For the preparation of the plasma physics multipole experiment Wendelstein 6 (‘W 6) which uses two concentric levitated superconducting rings the performance of Nb/sub 3/Sn tape wound coils is studied in the temperature range 4.2 to 17 K. The test coils investigated consist of different numbers of double pancakes made from 5 mm wide, G.E. tape with 22 cm i.d. and 32 cm o.d. Below about 11 K the quenches are caused by magnetic instability determined by a critical value of the maximum radial field B/sub Rmax/ almost independent of conductor rating, coil geometry and operation in liquid or gaseous He. Depending on the charging rate B/sub Rmax/ Is 15 to 22 kG, in a few cases 27 /spl plusmn/ 1 kG, in L.He. With increased temperature B/sub Rmax/ decreases to 14 /spl plusmn/ 4 kG at 11 K and to 8 /spl plusmn/ 3 kG at 14 K. Interleaving the windings with aluminum tape 30 and 50 u thick in an effort to stabilize the coils did not significantly alter the quenching behaviour although the same fields are reached with less superconducting tape. The anticipated operation of the W 6 device is discussed on the basis of these test results. In a specific mode of W 6 operation an improvement is expected when using aluminum interleaved superconductor.         Investigation of Cryogenic Stability and Reliability of Operation of Nb/sub 3/Sn Coils in Helium Gas Environment    A.P. Martinelli and S.L. Wipf Summary: The optimum operating temperature of coils with regard to economy of refrigeration and price of superconductor is above 4.2/spl deg/K. The performance of Nb/sub 3/Sn coils made of 2, 4, and 8 pancakes (ID 22 cm, OD 32 cm, tape width 0.5 cm) was tested in the 4.2 - 17/spl deg/K range. The cryogenic stability limit is calculated in liquid helium to be 90 A and is measured to be 70 A in gas at 4.2/spl deg/K, dropping to about 20 A when T approaches T/sub c/. Above these current limits, i.e. in the metastable range, the coils were tested for their response to local heating, which was applied in steady state (isothermal disturbance) or as a pulse (adiabatic disturbance) of increasing power until quench occurs. A model of the coil response to local heating is developed and compared with the experimental results.         The Economics of Large Superconducting Toroidal Magnets for Fusion Reactors    M.S. Lubell, H.M. Long, J.N. Luton Jr and W.C.T. Stoddart Summary: The encouraging results over the last few years in plasma research have generated renewed optimism that fusion feasibility will be demonstrated in the coming decade. Assuming that such is the case, the next logical step is the construction of a prototype power reactor. If this reactor employs plasma containment by intense magnetic fields, it is highly likely that superconducting magnets will be required for economic reasons. We have previously performed a study on the engineering design of a large syperconducting magnet system in a toroidal geometry. In this study (hereafter referred to as [I]), we considered a toroidal field B/sub o/ = 37 kG, a maximum field at the windings B/sub max/ = 80 kG, a major radius R = 10.5 m, end a minor coil radius r = 5.6 m, in a design using cryostatic stabilization of NbTi with copper. The design resulted in a magnet system with stored energy of 4 x 10/sup 10/ J requiring 4.75 x 10/sup6/ ft of composite NbTi conductor. The total weight of the system including conductor, stainless steel interleaving, bobbin, bobbin reinforcement, end central compression ring was about 9,025 tons and the total cost was $70,500,000. The cost breakdown of the major components is: compound conductor, 37%; structural reinforcements, 32%; winding, 13%; bobbins, 9%; and refrigeration, 4%.         Design and Economics of Large DC Fusion Magnets    J.R. Powell Summary: Projections are made for superconductor costs for dc fusion magnets, assuming superconductor production levels appropriate to an economy some time after 2000 AD in which a large fraction of the new electrical power plants are fusion reactors. The detailed projections are made on the basis of present (1971) conductor characteristics and processing technology. It is found that the very great increase in production of superconductor material that would be associated with a fusion power reactor economy should greatly reduce superconductor cost, in some cases by more than an order of magnitude. No allowance is made for large-scale production for other purposes, which well may be the case, and which should lead to even lower costs. It is also found that material costs should strong ly dominate total conductor cost. The projected conductor costs amount to only a few $/kW(e) for the fusion reactor designs that have been proposed, and are almost an order of magnitude smaller than magnet structure costs.         Operation of the Levitated Superconducting Ring in the Princeton Floating Multipole Machine    J. File and P. Bonanos Summary: The Princeton Floating Multipole Machine, FM-l, a plasma physics experimental device, has been operating as a spherator since August 1971. The levitated poloidal field coil is a Nb/sub 3/Sn superconducting ring operable up to 375,000 ampere-turns and is sixty inches in major diameter. The coil is mounted in an isolated isochoric Dewar, and plasma physics experiments are performed with the ring levitated and stabilized by a system similar to, but improved over, those previously reported. Two such rings have been built and are described including magnetic, electrical, mechanical, cryogenic and superconducting properties.         A 12-Coil Superconducting: "Bumpy Torus" Magnet Facility for Plasma Research    J.R. Roth, A.D. Holmes, T.A. Keller and W.M. Krawczonek Summary: A retrospective summary is presented of the performance of the two-coil superconducting pilot rig which preceded the NASA Lewis bumpy torus. This pilot rig was operated for 550 experimental runs over a period of 7 years. The long term degradation of certain subsystems of this apparatus have implications for the design of similar facilities. The NASA Lewis bumpy torus facility consists of 12 superconducting coils, each with a 19 cm i.d. and capable of producing magnetic field strengths of 3.0 teslas on their axes. The magnets are equally spaced around a major circumference 1.52 m in diameter, and are mounted with the major axis of the torus vertical in a single vacuum tank 2.59 m in diameter. The design value of maximum magnetic field on the magnetic axis (3.0 T) has been reached and exceeded. A maximum magnetic field of 3.23 T has been held for a period of 60 minutes, and the coils have not gone normal. When the coils were charged up to a maximum magnetic field of 3.35 T, the coil system was driven normal without damage to the facility.         Critical Fields and Critical Currents of High T/sub c/ Superconductors    E.J. Saur Summary: This paper gives a brief review of the critical data of type II superconductors with high T/sub c/ which might be important for future applications, namely: solid solution alloys of bcc type, /spl Beta/-W (A-15) type compounds, NaCl (B-l) type compounds and C-15 alloys (Laves phases), prepared with various methods in different shapes.         V/sub 3/Ga and other High-Field Superconductors Being Developed in Japan    K. Tachikawa Summary: Processings and properties of V/sub 3/Ga and other superconducting compounds being developed in Japan are described. Superconducting V/sub 3/Ga tapes produced by a surface diffusion process seem to be capable of generating fields as high as 180 kOe. Multi-filamentary V/sub 3/Ga wires made by a composite process seem to be useful for AC applications. Other A-15 type crystal structure materials, e.g., (Nb,Zr)/sub 3/Sn made by diffusion process and ternary compounds based on Nb/sub 3/Al have also been investigated. Upper critical fields exceeding 250 kOe have been obtained at 4.2 K, both in NbN films made by a reactive sputtering and in ternary Laves phase compounds based on V/sub 2/Hf.         Niobium-Tin Technology    C.H. Rosner Summary: Nb/sub 3/Sn, the first superconductor discovered to have high magnetic field properties and magnet potential, has undergone considerable study and development during the past decade. Conductors produced on the basis of various processing approaches and data on present day characteristics are presented in terms of current density, technological utility and applications made possible by the increasing availability of 150 kG Nb/sub 3/Sn magnets. Further conductor developments towards obtaining increased stability and mechanical strength as well as suitability for devices involving both d-c and varying fields are discussed, including high purity aluminum clad tapes as well as multifilamentary Nb/sub 3/Sn superconductors.         Filamentary Composite Superconductors for Pulsed Magnets    M.N. Wilson Summary: Composites containing up to 9000 filaments of niobium titanium are now being tested for use in pulsed magnets. It would be advantageous to go to still higher numbers but this would increase the coupling between filaments and therefore increase losses and decrease stability. The paper tries to see how this coupling will limit N, the number of filaments which can usefully be put into a composite. Magnetization and self field effects are treated separately. A new theory of magnetization in three component composites is presented and its implications for N are discussed. Self field theory is extended and two new mechanisms are suggested which could, in practice, reduce the magnitude of the self field effect. It is concluded that 20,000 filaments are now possible and that N could eventually be pushed as high as 10/sup 5/.         Superconductors for Pulsed Magnets    A.D. McInturff Summary: In this paper procedures are presented for obtaining multifilamentary Nb-Ti composites which can be formed into conductors (braids) for use in winding pulsed magnets (other multifilamentary superconductors can be treated similarly). The resulting conductor, in general, will not be "cryogenically" stable, but will satisfy both adiabatic, and dynamic stability criterion over the frequency range it is designed to operate. The rate of magnetic field change will however be restricted to less than 10.0 tesla/second.         Properties of Superconducting Nb/sub 3/Ga Materials    S. Foner, E.J. McNiff Jr., L.J. Vieland, A. Wicklund, R.E. Miller and G.W. Webb Summary: The upper critical field, H/sub C2/, versus temperature, T, has been measured in a series of Nb/sub x/Ga/sub 1-x/ materials. When properly fabricated the stoichiometric material, Nb/sub 3/Ga, yields T/sub c/ =20.3 K - the highest yet reported for a binary alloy. Measurements of H/sub C2/(T) with dc fields (to 210 kG) and pulsed fields show: 1) a closely linear variation of H/sub C2/(T) versus T near T/sub c/, 2) (dH/sub C2//dT)T/sub c/ varies from /spl equiv/20 to 25 kG/K and 3) the H/sub C2/(T) data show no appreciable evidence of Pauli paramagnetic limiting. Values of H/sub C2/(4.2 K) vary from 340 kG to 135 kGfor materials with T/sub c/=20.0K and 13.3K resoectivelv. Preliminary works shows that Nb-Ga materials with T/sub c//spl sime/ 19 K can be made by chemical vapor deposition (CVD), a process commonly used for producing commercial superconducting tape. Preliminary measurements in-15/spl equiv//spl mu/ thick(CVD) Nb-Ga samples yieldcritical currents comparable to those of Nb/sub 3/Sn (CVD) tape for fields < 170kG.         The Synthesis of A15 Nb-Ga Compounds having High T/sub c/'s    D.W. Deis, R.D. Blaugher, J.K. Hulm and J.R. Gavaler Summary: The superconducting transition temperatures of Nb-Ga alloys with Ga contents between 20 and 37.5 atomic percent have been studied as a function of heat treatment. This work indicates that Nb-Ga material with transitions close to 20°K can only be obtained by rapid cooling or quenching from high temperatures in the vicinity of 1800°C followed by low temperature annealing around 700°C. The increase in T/sub c/ observed after annealing at 700°C is suggestive of a mechanism involving the degree of long range atomic ordering.         Critical Currents in Granular Superconductors    J.H.P. Watson Summary: This paper describes measurements of the critical current density J/sub c/ for superconducting lead, indium and lead bismuth alloys in porous glass as a function of temperature and magnetic field. The results are interpreted in terms of a simple model.         Upper Critical Fields of Superconducting Laves Phases in V-Hf-X Ternary Alloys    K. Inoue and K. Tachikawa Summary: Pronounced improvements in upper critical field, H/sub c2/, have been achieved by the addition of zirconium, niobium, tantalum, and chromium to V/sub 2/Hf, C-15 type crystal structure Laves phase in V-Hf alloys. The highest H/sub c2/(4.2 K) obtained in V-Hf-Zr, V-Hf-Nb, V-Hf-Ta, and V-Hf-Cr ternary alloys are 240 kOe, 257 kOe, 261 kOe, and 234 kOe, respectively. Large electronic specific heat coefficient, normal state resistivity, and spin-orbit-scattering effect due to heavy hafnium atoms, seem to cause high H/sub c2/ in this type of material. A sign of low temperature lattice instability, like the case of /spl Beta/-W type compound, is observed in the temperature dependence of the electrical resistivity, magnetic susceptibility, and lattice parameter of these Laves phase compounds.         Superconductivity in Thin Films of the Mo-Re System    J.R. Gavaler, M.A. Janocko, J.K. Hulm and C.K. Jones Summary: A series of Mo-Re alloy films has been prepared by sputtering from a composite molybdenum and rhenium cathode. These films were deposited in an ultra-high purity environment onto sapphire substrates which were held at temperatures ranging from 400°C to 1300°C. Maximum transition temperatures observed were /spl equiv/ 15 K which is significantly greater than the highest reported bulk values. Critical current and field characteristics also were found to be considerably greater in the films compared to corresponding bulk samples. Upper critical fields of over 100 kOe were measured in the highest T/sub c/ films - more than a factor of four higher mum values reported for the bulk. These enhanced properties are discussed in relation to the structural characteristics of the sputtered films.         Magneto-Optical Studies of Superconductors at High Transport Current Densities    R.P. Huebener and R.T. Kampwirth Summary: We have investigated the current-induced magnetic flux structure in microstrips of superconducting lead and indium with a thickness between 4 and 8 /spl mu/m using a high-resolution magneto-optical method. The applied electrical transport current had an average density between 10/sup 5/ and 10/sup 6/ A/cm/sup 2/. The current-induced magnetic structure consists of narrow "channels" of normal material which grow abruptly from both edges to the center of the strip. The number of these normal channels increases with the transport current. The magnetic field in these channels has, of course, opposite sign for the two sides of the strip. The abrupt growth of each normal channel from the edge to the center of the strip is associated with a magnetic instability similar to the kink instability in magneto-hydrodynamics. Simultaneously with the appearance of the first normal channels, resistive voltages are detected in the specimens.         Dependence of J/sub c/ of Annealed Nb-Zr on Amount of Deformation Introduced Prior to Annealing    I. Milne and T.R. Finlayson Summary: Critical current densities (J/sub c/) in Nb-26%Zr and Nb-32%Zr were studied as a function of deformation by rolling both before and after annealing the material. Unannealed, the J/sub c/ increased with deformation. After annealing the maximum J/sub c/ obtained stabilized after 80% reduction in area, when the flux pinning constituent was /spl Beta//sub Zr/ precipitate. The volume fraction of /spl Beta//sub Zr/ increased with Zr content and with deformation. The J/sub c/'s obtained in these alloys were much lower than we obtained previously in Nb-25%Zr drawn wire and Nb-40%Zr rolled foil. In the Nb-25%Zr because of the good purity of this material precipitation was on too Small a scale to prevent polygonization of the dislocation substructure, unlike in the alloys studied here. This polygonized structure was more efficient at pinning flux than the precipitation structure of the Nb-26%Zr or the Nb-32%Zr. In the Nb-40%Zr, however, a larger volume fraction of precipitate was available for flux pinning than in either of the alloys studied here and this produced material with a higher J/sub c/.         Relationship Between Defect Structure, Flux-Line Lattice and Metallurgical Treatment in Highfield Superconductor NbTi    H. Hillmann and D. Hauck Summary: Composites of Nb 50 weight % Ti alloys showing high density /spl alpha/-precipitates by alternating cold work and heat treatment have been further cold worked. The following results were found by measurements of the critical current density and critical Lorentz force: 1. Current density increases with increasing cold work, exceeding a maximum value and decreasing by further cold work. 2. For different external fields the maxima of j/sub c/ (d) (d..... composite diameter) corresponds to different degree of cold work. 3. The pinning force shows also a maximum shifting to higher inductions B for stronger coldwork and corresponding to a decreasing slope of the j/sub c/(B) curve. By these results a model is given for the relationship of metal physical process effected by metallurgical treatment on the one hand and physical properties on the other. Under special conditions the occurence of relative peaks corresponding to a matching between flux line lattice and pinningsite distribution could be demonstrated.         Change in Critical Current of Superconducting NbTi by Neutron Irradiation    M. Soell, S.L. Wipf and G. Vogl Summary: Nb-50 wt % Ti (Nb-66 at % Ti) wires 11 and 21 /spl mu/ in diameter were exposed at 5/spl deg/K to neutron irradiation (E > O,l MeV) in the Munich research reactor at Garching. The critical currents as a function of a transverse magnetic field, measured immediately afterwards, showed for all wires a reduction from the original values. Subsequent five-minute annealing at different temperatures brought an improvement in the critical current each time. In some cases the original values were recovered.         Experimental Test of the Effect of Precipitate Pinning on Mixed State rf Loss and "Depinning Frequency" of Type II Superconductors    L.S. Weinman, J.B. Lewis III and R.M. Rose Summary: Mixed-state rf loss measurements were made on controlled specimens to test the relation between "depinning frequency" as defined in the currently accepted models and the critical Lorentz force for pinning. Precipitation of the second phase from the supersaturated Pb-12.9 (atomic) % Sn solid solution increased magnetic irreversibility substantially (as expected) but did not change the depinning frequency.         A Flux Flow Memory Switch    A.G. Putz, M. Steingart and E.J. Kramer Summary: A memory switch, based on the multiple-valued voltage-current characteristic of a plastically deformed type II superconductor, is described. Switching to the non-zero voltage ("on") state is accomplished with a current pulse sufficient to cause flux flow, which we presume disrupts the pin matching and/or perfection of the flux line lattice (FLL). The minimum current pulse duration to cause this switching is /spl equiv/100/spl mu/s at a peak electric field of 4/spl mu/V/cm. Switching back to the zero voltage ("off") state is accomplished by sending a current pulse sufficient to heat the crystal above the critical temperature T/sub c/(H). In our experiments heating is principally at a resistive spot weld in series with the crystal and in good thermal contact with it.         Energy Considerations Regarding the Propagation of Field Penetration Along Type II Superconductor Wires    M.S. Walker and J.K. Hulm Summary: The decay of persistent currents has been triggered in a number of Nb-25% Zr wires situated in changing longitudinal magnetic fields at 4.2/spl deg/K. Under favorable conditions the decay was observed to propagate from the heater trigger through two search coils spaced along the wire. Propa ation velocities were found to range from 2 x 10/sup 4/ to 10/sup 6/ cm/sec, exceeding the speed of sound in some instances. The heat inputs required to start propagation, propagation velocities are related to the stored energy released during the decay process. An electromagnetic propagation mechanism is postulated to explain the high propagation velocities.         The Velocity of Propagation of Flux Jumps Along Type II Superconducting Wires in Axial Fields    J. Bussiere and M.A.R. LeBlanc Summary: Measurements of the propagation of magnetic instabilities or flux jumps are presented for wires of NbTi, NbZr, and pure Nb. The velocities range between 10/sup 5/ and 10/sup 6/ cm/s for the alloys and 10/ sup/4 and 10/sup 5/ cm/s for the pure Nb. For a given material the velocity is seen to increase as the change in magnetization /spl utri/<4/spl pi/M> associated with the flux jump increases. A comparison between the velocities of the different materials indicates that the velocity also increases with the normal state resistivity. Qualitative arguments are presented pointing towards a radial diffusion type process together with an electromagnetic coupling between adjacent regions as the basis of the mechanism causing the propagation.         Magnetic Losses in a 500 k0e/s Pulsed Superconducting Solenoid    T.R. Haller Summary: In order to meet demands for field cycling NMR studies, a 3.5 cm bore NbTi solenoid has been developed having a field uniformity of 1 part in 10/sup 4/ in a 1 cm DSV. This solenoid has been cycled many times at up to 26 k0e peak to peak at 10 Hz with no evidence of normalcy. Frequencies of up to 108 Hz have been successfully achieved at reduced field strengths. The design utilizes single core copper stabilized superconductor with interlayer cooling channels. Surface heat flux is thereby kept below nucleate boiling limits. Testing was performed by discharging a capacitor bank through the coil and observing the decay of the resultant sinusoidal voltage waveform from which magnet losses could be calculated. By varying the capacitance and voltage, data were obtained for a variety of frequencies and field strengths. Measured losses were found to be in general agreement with those predicted by theory when superconductor hysteresis, copper eddy current, and copper transport current mechanisms are considered.         A.C. Permeability Studies of Ternary Alloys at Cryogenic Temperatures    R. Lepper, E.G. Wolff and G.J. Mills Summary: A differential ac permeability technique was developed and used to study the Shubnikov phase region in the Ti-6Al-4V aircraft alloy. The effects of metallurgical processing and microstructure were correlated with critical temperature and complex permeability/ susceptibility at applied fields up to 0.7 tesla. Control of the complex susceptibility (/spl chi/', /spl chi/") and critical temperature (over the range /spl equiv/1°K to > 4°K) could be independently achieved by control of the morphology of the various metallurgical phases obtainable through conventional heat treatments. Modification of the technique for studies in the range 0.3 to 77°K, for dc permeability and for critical current measurements are outlined. Implications for the control of superconducting properties of complex alloys for cryogenic devices are outlined, including methods to maximize T/sub c/ and minimize /spl chi/".         AC Studies of a Superconducting Nb-52at.%Ti Alloy    S.T. Sekula and R.H. Kernohan Summary: Using a Hartshorn bridge in conjunction with a lock-in amplifier, a signal V/sub L/, proportional to the component of the complex permeability directly related to the losses in a sample, has been measured for a cold-worked Nb-52at.%Ti specimen and a sample heat treated at 1100/spl deg/C for 1 h. Measurements were carried out at 4.2 K in a dc field H varying from zero to 7 kOe and in a superposed ac (350 Hz) field of amplitude h up to 380 Oe. Power dissipation in the samples was observed to depend somewhat on previous magnetic history. In the cold-worked sample the dependence of energy loss on the amplitude was shown to be cubic for large values of H and h/sub o/, while at smaller values the dependence was seen to be greater than cubic. Measurements of V/sub L/ vs H for the cold-worked sample reveal a linear dependence of V/sub L/ at the higher values of H. Application of the Bean-London model to these data then shows that the field dependence of the critical current density J/sub c/ can be described by a relation of the Kim-Hempstead form J/sub c/ = /spl alpha// (H + H/sub o).         The Temperature Dependence of Superconducting Critical Current Densities of Multifilamentary A-15 Composite Wires    J.E. Crow and M. Suenaga Summary: Recently it has been demonstrated that multifilamentary superconducting composites can be made with A-15 composites, thus significantly increasing the transition temperature and the critical field over that of conventional Nb alloy composites. Critical currents have been measured as a function of temperature and magnetic field for composites containing filaments of Nb/sub 3/Sn and V/sub 3/Ga. The measured critical current densi ies for these composites are comparable with those for V/sub 3/Ga tapes and commercial Nb/sub 3/Sn ribbons.         Geometric Reduction of the Critical Current Density in Multifilament Composite Superconductors    M.S. Walker Summary: Improved critical current stability and reduced AC losses have resulted from the construction of composites having many superconductor filaments embedded in a normal metal or alloy matrix. The losses are reduced by twisting the composites, and the twist pitch, L, is made small owing to an L/sup 2/ coupling loss dependence for sufficient twist. Composites with L as small as ten composite diameters are commonly made, but the need for more tightly twisted superconductorsmay arise. The present work shows, however, that there is a limit to the amount of twist that can usefully be employed, since the reduction of L changes the geometry of the superconductor in such a way that the effective critical current of the wire is also reduced. As L approaches several wire diameters the decrease in the critical current becomes severe. This geometric limit has been observed by us in NbTi-copper multifilamentary composite superconductors and is explained by the simple analysis which follows. Experimental data supporting the theory are also presented.         Superconducting Properties of Multifilamentary V/sub 3/Si Wires    M. Suenaga and W.B. Sampson Summary: A composite superconductor consisting of V/sub 3/Si filaments in a Cu-Si matrix was made by the diffusion process which has also been used to produce V/sub 3/Ga and Nb/sub 3/Sn composites. The critical temperature, T/sub c/ , and the critical current density, J/subc/(H), of this wire were measured for various heat treatments. Degradation of the critical current by bending was also investigated. These results for V/sub c/Si wires are compared with those for Nb/sub 3/Sn and V/sub 3/Ga wires which were processed similarly and had identical physical geometries.         Coupling in Superconducting Braids and Cables    W. Gilbert, F. Vqelker, R. Acker and J. Kaugerts Summary: In pulsed, low loss, superconducting magnets one often uses high current cables or braids composed of a number of composite wires, each containing hundreds of fine NbTi filaments. Cables in the 500 - 3000 ampere range, combining 50 - 150 wires, with filament diameters of 5.6 - 11/spl mu/ have been tested for inter-wire coupling by measuring the pulse losses in solenoid msgnets wound from various braids and cables. Losses were electrically determined with a newly developed digital-multiplier-integrator system. The measured dependence of the couplings upon applied magnetic field changes end cable geometry are in reasonable agreement with our intra-cable and intrarbraid coupling theories. The losses in several magnets do not double their superconducting hysteretic zero B cyclic loss until the B exceeds 100 kG set/sup -1/.         Low Temperature Electron Irradiation of Multifilament Superconductors    D.G. Schweitzer, D.M. Parkin, M. Garber and A. Goland Summary: Property changes in multifilament superconductors during and after 1 MeV electron irradiations at 3/spl deg/K are described. The studies include measurements on direct and indirect heat transfer problems associated with irradiations where the sample is maintained in the superconducting state during irradiation. Techniques utilizing the properties of the superconductor were developed to obtain accurate values of the flux and sample temperature during irradiation. Changes in the critical current with temperature and in fields to 60 kilogauss are described. The large changes observed after initial electron irradiations were found to be caused by heating effects and not by defects produced by the electrons. The changes after irradiation are compared to similar changes which can be induced by shortterm heat treatments.         Property Changes in Multifilament Superconductors Due to High Temperature Heat Treatments and Electron Irradiations    D.M. Parkin and D.G. Schweitzer Summary: Multifilament 50% Nb-Ti 50% Cu wires show large changes in critical current with heat treatments from 600°C to 700°C. Short heat treatments at 700°C reduce the value of I/sub c/ in an applied field of 40 kG to 27% of the as received value. Unclad stripped wires also show reductions in I/sub c/ . Measurements after 300°C 1 MeV electron irradiations to 10/sup 20/ e/cm/sup 2/ show no changes in the value of I/sub c/.         Magnetic Field Effects on the Thermal Conductances of Type II Superconductor-Copper Junctions    Y.M. Chang and T.H.K. Frederking Summary: Magnetic field effects on the thermal conductances (h) of type II superconductor-copper junctions have been investigated up to the upper critical field H/sub c2/ (Nb). A Nb-Cu junction was formed by casting an upper Cu-cylinder to a lower Nc-cylinder. An external magnetic field (H) was applied perpendicular to the interface and parallel to the axis of the cylindrical vacuum-insulated specimen. Heat flowed along the axis from the Nb-cylinder to the Cu-cylinder placed in contact with liquid He. In the Meissner state, h stayed constant up to the onset of flux line entry. After penetration of flux into the sample, h increased monotonically in the mixed state as H was raised to H/sub c2/. Upon decrease of the field, h remained relatively large without returning to the value at zero applied field (indicating flux trapping). The thermal resistance of the junction was two to three orders of magnitude larger than the resistance of a Nb-cylinder segment with a height equal to the junction zone thickness. Similar experimentsowith commercial NbTi-Cu junctions showed a large thermal resistance independent of H up to 30 kOe at 2/spl deg/K. At 4/spl deg/K, h was of the order of magnitude 10/sup-2/ W cm/sup -2/ /spl deg/K/sup -1/ and smaller than the Nb-Cu - values.         Experiments on Stability of Nb/sub 3/Sn Ribbons    K.R. Efferson and H.M. Long Summary: The major instability problem in Nb/sub 3/Sn ribbon superconductors is known to be due to flux jumps caused by magnetic field components perpendicular to the face of the ribbons (H/sub 1/) Likewise, techniques which are intended to prevent this instability are also well known and include 1) reducing the width of the ribbon, 2) using low current rated material in regions of large H/sub 1/, 3) paralleling the ribbon with good electrical conducting material, and 4) providing as much cooling as possible. The decision, in 1968, to employ Nb/sub 3/Sn ribbon in IMP, a large plasma physics research facility, was made without full knowledge of how bad the instability really was. While difficult force problems and machining and assembly problems were being solved, experiments were performed to determine the best way to reach the IMP quadrupole design point (13,500 A/cm/sup 2/ = (j), H/sub max/ = 85 kG, H/sub 1/ = 62 kG). The stability question was answered by performing experiments with relatively large test coils called "cusp coils" which showed that stabilization could be achieved by cowinding 0.006 in. aluminum ribbon (P/sub 300//P/sub 4.2/ > 2000) along with the Nb/sub 3/Sn ribbon.         Aluminum Stabilized Nb-Ti Superconductor    A. El Bindari Summary: The use of a normal metal of good electrical conductivity in intimate contact with a superconductor has been widely used-in the past few years. The amount of the substrate material required was thought to depend on the normal metal electrical conductivity. The higher the conductivity of the normal metal the smaller the amount of normal substrate required. However, we pointed out previously that the substrate main function is to increase the cooled perimeter of the superconductor. The conditions are such that the thermal conductivity or the dimensions are small enough to neglect temperature gradients inside the substrate.         A New Superconducting Composite with Low Hysteresis Loss    R.A. Popley, D.J. Sambrook, C.R. Walters and M.N. Wilson Summary: This paper describes a new way of making filamentary composites for use in pulsed magnets. It is hoped that the new technique will enable composites to be made which contain many more filaments than previously and yet have a low hysteresis loss and are stable. A special kind of extrusion canister forms the basis of the technique.         Low Frequency Measurements with Josephson Devices    J. Clarke Summary: This paper briefly surveys the application of Josephson devices to the measurement of low frequency magnetic fields and voltages. The various types of Josephson junctions are described. The sensitivities of DC and RF SQUIDS are compared, and the noise limits of these devices discussed. The inherent noise of a device with inductance 10/sup -9/ H is expected to be of order 10/sup -6/ /spl phi//sub 0/ //spl radic/Hz, whereas 10 the observed noise limit is typically , 10/sup -3/, 10/sup -4/ /spl phi//sub 0/ //spl radic/Hz, implying that noise in the room temperature electronics and /or environmental noise are the limiting factors. The magnetic field sensitivity of SQUIDS may be improved bv the use of a flux transformer to perhaps 10/sup -14/ /spl phi//sub 0/ //spl radic/Hz Transformer coupling also greatly extends the range of SQUIDS used as voltmeters: in the He/sup 4/ temperature range, it is possible for the measurement to be Johnson noise limited in circuits whose resistance is /spl lsim/1/spl Omega/.         Operating Characteristics of Cylindrical Thin Film Weak Link Circuits Used As the Sensing Element in Ultra-Sensitive Magnetometer System    M. Nisenoff Summary: This paper reviews the present state of development of thin film superconducting weak link devices. An equivalent circuit is presented for a weak link device, and an analysis is carried out describing the operation of a weak link device coupled to a LC resonant circuit using simple ac circuit theory. Expressions are obtained for the magnitude of the magnetic field dependent component of the RF impedance of the coupled circuit as a function of circuit parameters. Criteria are presented for the observation of the field dependent RF impedance as a function of circuit geometry and operation conditions.         Josephson Tunnel Junctions    J. Matisoo Summary: This paper deals specifically with Josephson tunnel junctions. That is, those structures in which the current transport from one bulk superconductor to the other is by electron tunneling. In general, these structures are very well characterized electrically and geometrically. Almost any size junction can be made. Specifically, tunnel junctions have : well defined geometry; well known conduction mechanism; well defined magnetic field properties; well-defined models which describe their behavior; well controlled j/sub 1/, the Josephson current density; large capacitance, and therefore low characteristic impedance.         A Review of the Properties and Applications of Superconducting Point Contacts    J.E. Zimmerman Summary: Superconducting small-area ("point") contacts are easily made in a number of forms, and are used in a wide variety of devices, some of which are quite highly evolved. For many practical purposes no special contact surface preparation is required. Electrical properties are often said to be "tunnel-junction like" or "metal bridge like," but the meaning of these terms is not clear. New evidence shows that perfectly-clean metallic contacts often exhibit all the features expected of lowcapacitance tunnel junctions. Permanently stable point-contact devices have been made by one or a combination of several techniques, but their vulnerability to electrical and other transients has led to the development of simple and effective adjusting mechinisms. Certain point contacts, with minimum possible shunt capacitance and shunt normal conductance, approach the ideal of pure Josephson current elements (i =i/sub o/ sin /spl theta/) more closely than any other type of Josephson junction, and, for this reason, appear to be the best type of junction for millimeterwave and far-infrared applications. Paradoxically, the dc-IV characteristics of such pure Josephson elements can be very complex if they are closely coupled to external circuit elements such as microwave cavities and resonances of impurity molecules.         Durable Thin-Film Josephson Tunnel Junctions    K. Schwidtal and R.D. Finnegan Summary: Nb-NbO/sub x/-Pb thin-film Josephson tunnel junctions have been prepared with any desired area resistivity, and with tunnel barrier layers that are reproducibly uniform, and remain so with time. Thermal cycling requires no special precautions. The normal tunnel resistance RNT changes with time t of junction storage at roan temperature only as R/sub NT/sup spl prop/t/ /sup -1/5 / . Junction preparation and parameters determining durability are described in detail.         Josephson and Giaever Effects with a Semiconducting Barrier of Variable Height    P. Cardinne, B. Manhes and M. Renard Summary: Josephson and Giaever effects are observed in plane junctions with evaporated semiconducting barrier (100-200 /apl Aring/) A model using semiconductor-metal properties allows us to explain the main experimental results. The important parameters governing the general behaviour are found to be the doping and the thermally excited electrons. Besides. certain results show deviation from tunneling properties of junctions with oxide barriers.         Magnetochemical studies with a New Ultrasensitive Superconducting Quantum Magnetometer    H.R. Hoenig, R.H. Wang, G.R. Rossman and J.E. Mercereau Summary: A magnetometer utilizing quantum superconductivity as the basis for the flux sensor element has been designed and used for biochemical susceptibility measurements in the temperature range from 1.5°K to 300°K. The sensitivity and reproducibility of this instrument have been tested by measurements on small amounts of material of well known susceptibilities. Using this instrument the temperature dependence of the magnetic susceptibilities of oxy- and metaquohemerythrin have been measured and for the first time their anti-ferromagnetic components have been unambigiously resolved. From this data the exchange coupling constants between the two high-spin iron (III) atoms in each subunit have been determined to be -77 and -134 cm/sup -l/ respectively.         Effects of Dynamics in the Flux Shuttle and other Josephson Circuits and Devices    T.A. Fulton Summary: The behavior of a variety of circuits employing Josephson junctions is discussed in terms of their mechanical analogs.         Thermal Fluctuation Noise in a Superconducting Flux Detector    J. Kurkijarvi and W.W. Webb Summary: The thermal fluctuation noise in superconducting quantum flux detectors biased at radio frequencies has been calculated using a recent theory by J. Kurkijarvi of the intrinsic fluctuations of a superconducting ring of inductance L/sub s/ closed by a Josephson junction of critical current i/sub c/. The spectral density at low frequencies is found to be <[/spl delta//spl phi//sub x/(0)]/sup 2/> = 90.5/f/sub RF/) {L/sub s/i/sub c//sup 1/3 / (2/spl pi/k/sub B/T//spl phi/sup o//sup 2/3 /(3/4//spl radic/2//sup 2/3 / x[1-(/spl phi//sub o//2/spl pi/Li/sub c)/sup 2]/sup 1/6 / }sup 2/ at temperature k/sub B/T in units of flux quanta /spl phi//sub o/. For typical flux detector parameters <[/spl delta//spl phi//sub x/(0)]/sup 2/>/sup 1/2 //(Hz)/sup 1/2 / /spl sim/ 2x10/sup -5//spl phi/sub o/. An expression for the plateau shape for the plot of detected tank circuit voltage versus drive current is also given.         The Use of Josephson Junctions for Noise Thermometry Below 1 Kelvin    R.J. Soulen Jr. and H. Marshak Summary: Kamper and Zimmerman have demonstrated that a Josephson junction connected in parallel to a resistor converts the Johnson noise voltage fluctuations into frequency fluctuations, and that the variance of these frequency fluctuations is simply related to absolute temperature. In order to make accurate measurements of temperature with this device, a fast data acquisition system consisting of a frequency counter interfaced to a small computer has been developed. This thermometer has been compared to a Co/sup 60/ y-ray anisotropy thermometer in the temperature,region of .020 to .050 K. Preliminary results indicate agreement to within 5%. We have used our results to redetermine the superconductive transition temperature of pure beryllium. Our value is .0228 K, 3mK lower than reported by Falge. Since our thermometers do not depend upon any calibration or extrapolation and only on some accurately and independently determined parameters of each system, our value of T/sub c/ is probably very close to the absolute temperature of the transition.         Response of the Self-Driven, Weakly Connected Superconducting Ring (ac-SQUID)    H. Kanter and A.H. Silver Summary: The response of a resonance circuit when coupled to a superconducting ring incorporating a small voltage biased Josephson junction was investigated. The Josephson frequency, w/sub o/, was varied over several multiples of the resonance, /spl omega//sub r/ (30 MHz). For /spl omega//sub o/ = /spl omega//sub r/ and small /spl Beta/ = 2eLI/sub c/ //spl planck/, the tank voltage amplitude varied proportionately to critical current but saturated for /spl B/ /spl sim/ 1. At /spl omega//sub o/ = 2/spl omega//sub r/ and /spl Beta/ /spl sim/ 1 parametric self-excitation was observed with amplitude saturation for large I/sub c/ similar to that observed for /spl omega/sub o/ = /spl omega//sub r/. Application of an external signal, v sin/omega/sub r/t , showed Fourier components of currents nearly described by pairs of Bessel function amplitudes as expected from modulation of the quantum phase. For /spl Beta/ small enough to avoid parametric excitation the response at /spl omega//sub o/ = 2/spl omega//sub r/ represented parametric amplification in the degenerate negative resistance mode. Since Josephson oscillations have been shown to occur well into the far infrared region, the latter effect may have considerable practical potential for self-pumped parametric amplification of weak millimeter and submillimeter signals.         Equivalent Circuits for Small Dayem Bridges    P.E. Gregers-Hansen, E. Hendricks, M.T. Levinsen and G.F. Pedersen Summary: An experimental investigation of small Dayem bridges (superconducting thin-film microbridges) prepared by a new method is reported. We have measured the I-V characteristics of these bridges at many different temperatures and in varying microwave fields. The experimental results are compared with analog computations on several simple equivalent circuits. The small Dayem bridges are found to be fairly well described by an equivalent circuit consisting of a resistor in parallel with a device determined by the two Josephson equations and driven by a constant current source. Deviations, however,occur. Near the transition temperature the substitution of a voltage source in series with a self-inductance can explain many of the observed deviations. At lower temperatures both a capacitor and a self-inductance must be added to the simple equivalent circuit to obtain qualitative agreement with experiment. Several of the experimentally observed deviations from analog calculations on the simple circuit cannot be explained by addition of lumped impedance elements, indicating the need for an approach based on more fundamental concepts.         Numerical Calculations of Mixing with Superconducting Weak Links    F. Auracher and T. Van Duzer Summary: We report here extensive numerical calculations on the mixing properties of superconducting weak links driven by two RF current sources at frequencies /spl omega//sub 1/ (local oscillator) and /spl omega//sub 2/ (signal) and biased with a dc current. We calculate, for small signal amplitudes (I/sub 2/), the IF voltage across the weak link as a function of the bias current, the local-oscillator amplitude I/spl 1/, and the dimensionless parameter K/spl 1/ = h /spl omega//sub 1//2eI/sub m/R, where I/sub m/ is the maximum dc Josephson current. We find two modes of operation depending on the proximity of /spl omega//sub 1/ and /spl omega//sub 2/ and the relative values of I/sub 1/ and I/spl 2/, as was observed by Grimes and Shapiro. For /spl omega/IF /spl ges/ spl omega//sub 1//10 and not-too-small signal amplitudes, additional steps occur in the dc I-V characteristics and we find a nonlinear IF response. When /spl omega//sub 1/ = /spl omega//sub 2/ and I/sub 2 << I/sub 1/ the response is linear in a certain range of bias current and conversion gain is possible for small values of K/sub 1/. For this linear mode of operation, we show that the IF response can be calculated from pairs of I-V characteristics with I/sub 2/ = 0 and two different values of local oscillator current.         Observation of Microwave Induced Steps in the I-V Characteristic of Mo-Re Dayem Bridges at Temperatures Above 12/spl deg/K    M.A. Janocko, J.R. Gavaler and C.K. Jones Summary: Steps induced by 9 GHz microwave radiation have been observed in the current-voltage curves of Mo-Re alloy Dayem bridges operating at temperatures up to 12.6/spl deg/K. This is the first time that a definite Josephson effect has been seen at these elevated temperatures in a thin film junction of the Dayem bridge type. Thus Josephson junctions having this stable and reproducible configuration can now be used at temperatures easily and efficiently obtainable with closed cycle refrigerators,         Application of Microsuperconductivity to High Frequency Detection    S. Shapiro Summary: This paper reviews the use of superconducting bolometers and of Josephson effect weak links as detectors for both broad-band and narrow-band signals from microwave frequencies to the far-infrared. Emphasis is on the basic principles and mechanisms of operation used in achieving reported speed, sensitivity and frequency response values. Superconducting thin-films operate as bolometers in either an isothermal mode, in which each element of the film is at the same temperature, or in a non-isothermal mode, in which a temperature gradient is established along the film. In the former case, with tight thermal contact to the surrounding liquid helium bath, time constants of 20 ns have been achieved at NEP values of about 10/sup -9/ W//spl radic/Hz. When designed with looser thermal contact to the bath, i.e., time constants of about l.s, similar bolometers have achieved NEP values of about10/sup -13/ W//spl radic/Hz. Non-thermal detectors employing the ac Josephson effect in superconducting weak links operate in several video modes for either broad-band or narrow-band signals: detection via a change in a junction's maximum zerovoltage current, or via modulation of an rf-induced step, or via a change in amplitude of a cavity-induced step. Heterodyne detection mechanisms include direct mixing of two rf input signals, mixing of harmonics of one rf input against another rf input, and self-mixing in which Josephson currents themselves serve as local oscillator to mix with an incident signal. Limiting values so far achieved include estimates of NEP of about 5 x 10/sup -15/ W/spl radic/Hz, speed of response better than 10 ns, and frequency response to 78 /spl mu/.         The Status of Superconductivity for RF Applications    J.P. Turneaure Summary: The RF applications of superconductivity are reviewed. A discussion of the techniques of manufacturing superconducting cavities is given along with the results that have been obtained in the frequency range of 100 MHz to 10 GHz. The superconductor Nb is emphasized.         Precise Electrical Measurements at Low Temperature    D.B. Sullivan Summary: The application of low temperature phenomena, particularly superconductivity, to electrical metrology is reviewed. The review includes a number of recent developments which involve measurement systems based on the quantum of magnetic flux as well as adaptations of classical concepts to low temperature devices. Quantities considered include radio frequency current, infrared frequency, and direct current and voltage. Concepts for secondary emf standards are also discussed.         Advances in Superconducting Instrument Systems    W.S. Goree Summary: In this paper technically advanced superconducting instrument systems will be described which utilize presently available superconducting materials, skills and techniques to provide to a wide variety of applications a reliable, high performance, easy-to-use capability. The instruments described have required a marriage of sophisticated electronics, low temperature physics, superconducting materials and vacuum technologies. In the design of these instruments emphasis has been placed on providing practical, cost effective solutions to specific user problems: It will be demonstrated that with the practical advent of superconducting shields,reliable thin film sensors, long storage life liquid helium cryostats, and imaginative use of the superconductive properties superconductivity has come of age and has passed definitively from the research laboratory and is now useful to all scientific and engineering research and development personnel. It seems likely that applications of superconductivity will impact every scientific discipline known to man.         Phase Stabilization of Superconducting Helical Accelerating Structures    G.J. Dick and K.W. Shepard Summary: Measurements on superconducting helical resonators in the 30-60 MHz region show mechanical deformation causing eigenfrequency shifts a factor of 10/sup 5/ greater than the intrinsic bandwidth due to radiation pressure at operating field levels, and shifts of 10/sup 2/ bandwidths due to ambient vibration. In order to operate a series of resonators as an accelerating structure, each resonator must be phase-locked to an external clock. We have developed control circuitry using RF feedback which locks the amplitude and phase of the voltage in a resonator at high Dower levels to that of a reference oscillator despite large changes in the eigenfrequency. Additionally, methods for increasing the mechanical stability of a superconducting helix with dielectric support have been developed. A sapphire support structure has been successfully tested in a superconducting resonator at high field levels without causing significant increases in power loss.         Investigation of Niobium Deflecting Cavity Models for Use in a Superconducting RF Particle Separator    W. Bauer, A. Citron, G. Dammertz, H.C. Eschelbacher, W. Jungst, H. Lengeler, H. Miller and E. Rathgeber Summary: A superconducting RF particle separator will be constructed for use with the CERN 300 GeV proton synchrotron. As an intermediate step towards this project a prototype separator will be tested in a beam from the 28 GeV machine at CERN. The main features of this test-separator are described in the first part of the paper. The second part gives a summary of recent results of Q- and peak field measurements on small test cavities at 2855 MHZ. The highest Q-value obtained so far in a deflecting cavity was 1.4/spl middot/10/sup 9/, the highest deflecting field was 3.0 MV/m corresponding to a peak magnetic field of 470 G. In the third part of the paper some thoughts and calculations on the RF joint problem are reported.         On the Variation of RF-Surface Resistance with Field Strength in Anodized Niobium Cavities    P. Kneisel, O. Stoltz and J. Halbritter Summary: Superconducting Nb cavities of low residual losses show unusual dependencies of the losses on RF field level. By anodizing Nb in a special way we have achieved in a S-band cavity residual losses R/sub res/<2/spl middot/10/sup -9//spl Omega/, the lowest measured at these frequencies till now, and breakdown fields of about 400 Oe. Together with these small residual losses the surface resistance becomes strongly RF field strength dependent due to unknown mechanisms. To clear up these mechanisms, we have studied the R(H)-dependence in different modes between 2 and 4 GHz at different temperatures. As a result, the low fieid structures in R(H) belong to a surface sheath of Nb and are very sensitive, e.g. can be changed by electron impact. The measurement at high RF field strength show sudden changes of R(H) and a breakdown field depending like [1-(T/T/sub c/)/sup 2/] on temperature in modes with negligible electron loading.         RF Breakdown of Superconducting Cavities    J. Halbritter Summary: Whereas in normalconducting cavities the RF field strengths are limited by discharges due to high electric fields, as yet in superconducting cavities the actual limitation is an RF breakdown related to the magnetic field, i.e. due to the dissipation of shielding currents. This new type of breakdown is due to the RF absorption strongly increasing with temperature, especially near the phase transition from the superconducting to the normalconducting state. Like in all thermodynamic phase transitions of first order, the breakdown is initiated by nucleation of normalconducting regions. The nucleation is eased by surface in homogeneities or by local heating, e.g. due to the impact of charged particles. Because the dimension of the normal regions must be of the order of the coherence length /spl xi/, it will be more difficult to reach breakdown fields H/sub crit/ of about H/sub c/(T) in materials with short coherence length, e.g. in Nb, than e.g. in In, Sn, Pb. The proposed model explains the observed dependence of H/sub crit/ on material parameters or temperature, which shows that the thermal conductivity does not define H/sub crit/.         Effect of Surface Conditions on some Superconducting Properties of Niobium    M. Strongin, H.H. Farrell, C. Varmazis, H.J. Halama, O.F. Kammerer, M.N. Varma and J.M. Dickey Summary: Although the exact mechanism for rf breakdown is not understood it appears likely that the details of the structure and impurity content at the surface of the superconductor are crucial factors. We discuss measurements of gaseous impurities on the niobium surface which indicate higher oxygen levels than the bulk concentrations. Superconducting penetration depth measurements with various bulk oxygen concentrations are discussed, and they also indicate higher amounts of oxygen in the surface regime. Finally, the properties of thin films of Nb/sub 3/Sn grown on niobium, which can be used as a high T/sub c/ protective layer for the delicate niobium surface, are discussed.         Some Superconductive Thin Film Devices for Radio and Microwave Frequencies    C.A. Passow, V.L. Newhouse and R.L. Gunshor Summary: It is shown that the low ohmic losses of superconductors make possible the construction of radio and microwave devices which are one or more orders of magnitude smaller than their room temperature counterparts, and exhibit improved performance. The possibility of miniaturization permits the use of thin film techniques with the attendant economies of fabrication by evaporation and photo-etching. Three thin film devices are described; a non-dispersive ultracompact delay line, a dispersive line intended for pulse compression, and a tuneable line which uses the kinetic inductance effect. The advantages and disadvantages of superconductors vis a vis room temperature microwave acoustic techniques are discussed.         A Superconducting Time-Variant Filtering System    G.D. Arndt, T.W. Eggleston, C.W. Alworth and C.R. Haden Summary: This paper describes the development of a laboratory test facility for studying the tracking capabilities of a superconducting time-varying filter system. A closed-cycle helium refrigerator provides cooling to the cavity, which is lead-plated, and to the semiconductor. This technique is still in the experimental stage, primarily because of present difficulties in achieving high Q cavities.         Superconducting Gravitational Detector    G.J. Dick and H.C. Yen Summary: We have analyzed and are developing a technique to detect very small displacements using superconducting resonators and existing semiconductor technology. This technique obtains a sensitivity to fractional changes in frequency of 10/sup -14/ at a modulation frequency of 1 kHz with a time constant of one second. For a resonator with a characteristic size of 10/spl mu/ this gives a distance sensitivity of 10/sup -17/ cm. The sensitivity of the method is limited by noise in the semiconducting phase detectors presently available. Properties required of the superconducting resonators are not stringent; Q's and field levels are well within the state of the art. Such a detector is a parametric transducer. Since it does not introduce mechanical losses, it can be usea with strain multiplication techniques to give very gooa sensitivity to impulsive vibrations in either a room temperature or a cryogenically cooled resonant gravitational antenna.         RF Surface Impedance Measurements on Superconducting Niobium Films    W.J. SooHoo and R.L. Coren Summary: Nb films, 100 A to 700 A thick, were evaporated at 10/sup -8/ torr onto unheated glass substrates. Using a 10 GHz bridge the complex reflection coefficient waa measured at 4.2 K as a magnetic field varied normal to the film. H/sub c2/ is 7-9 kOe; magnetic hysteresis effects are observed. The data are analyzed using an oscillating fluxoid model. At this frequency direct pinning effects can be neglected. The field variations are obtained for n, the viscosity coefficient and M the mass of the fluxoid bundle. The values found are: /spl eta/ = 10/sup -13/ joule sec/m/sup 3/ and M /spl sime/ 5(10)/sup 6/ electrons/m/.         The Superconductor Maser: A Calculation of the Gain From the Two-level Model and the BCS Theory, and some New Experimental Results    W.N. Mathews Jr., W.D. Gregory, L. Leopold, J. Bostock and J. George Summary: A theory for the gain due to stimulated emission of radiation at the gap frequency in superconductors is presented. Within the context of first order time-dependent perturbation theory, the twolevel model recently developed by Fife and Gygax, and the BCS microscopic theory of superconductivity, it is found that positive gain is possible, both near absolute zero and very near the critical temperature. Recent experiments furnish further evidence for the existence of radiative emission from appropriately formed N-S point contact tunnel junctions.         Quantum Mechanical Measurement of rf Attenuation    R.A. Kamper, M.B. Simmonds, R.T. Adair and C.A. Hoer Summary: We have used a broadband Superconducting Quantum Interference Device (SQUID), operating at a frequency of 9 GHz, as a sensor of current at lower radio frequencies. The periodic nature of the response of the SQUID enabled us to measure variations in rf attenuation directly. The results of such a measurement were in agreement with the NBS Calibration Service to within /spl plusmn/ 0.004 dB over a dynamic range of 40 dB. We also discuss other applications of this SQUID to rf measurements.         Radiation Generation and Detection Characteristics of Arrays of Point Contact Josephson Junctions    D.J. Replici, L. Leopold, W.D. Gregory, M. Behravesh and T. Thompson Summary: Ten arrays of 180 Josephson junction point contacts each of the type first studied by Clark have been investigated. The arrays were composed of an ordered 10 x 10 matrix of tin spheres 1.1 mm in diameter. The radiation generation and detection capabilities of the arrays were studied using a resonant structure formed by placing the arrays between two moveable parallel mirrors. In some cases, one of the mirrors was external to the cryostat, thus delivering the radiation out of the dewar. Other experiments were performed by shining 97 GHz klystron radiation on the array. The results indicate a rich spectrum of radiative frequencies, from the mm to hundreds of microns wavelength region, with some predominance at I.2 mm and 202 microns. A new estimate of the power developed by the arrays (40 nanowatts) is in agreement with a previous estimate of Clark.         Weakly Superconducting, Thin-Film Structures as Radiation Detectors    R.K. Kirschman Summary: A thin-film superconducting structure is described, which-on the basis of low-frequency measurements-shows promise as a microwave and infrared detector.         Josephson Junction One Millimeter Microwave Source: Coupling Outside a Dewar    B.T. Ulrich and E.O. Kluth Summary: Microwave radiation at short millimeter wavelengths from a Josephson junction has been transmitted outside a dewar for use in a room temperature environment. This paper describes the experiments that demonstrate the utility of a Josephson junction as a millimeter microwave source. A single point contact superconducting junction was used as a microwave emitter at discrete wavelengths between 1.1 mm and 2.6 mm. These wavelengths were determined by resonances of a cavity tightly coupled to the Josephson junction, biased to a voltage corresponding to the cavity frequency. The emitting Josephson junction also was used as a detector of its own radiation, and gave a signal to noise ratio of 10/sup 3/ /spl radic/Hz/. We expect the Josephson junction microwave source to find applications in laboratory microwave measurements such as the measurement of transmission and reflectance of materials at short millimeter wavelengths.         Direct Demonstration of Josephson Frequency Conversion    A. Longacre Jr. Summary: Josephson frequency conversion, a mode of operating the Josephson junction in which an input signal is up or down-converted by mixing with the ac Josephson currents, has been demonstrated and studied in superconducting point-contact junctions at microwave frequencies. In particular, downconversion from 24 GHz to 9.3 GHz was directly achieved, and evidence of conversion from 640 GHz to 20 GHz was also obtained. An analog simulation of the experiments has assisted in understanding these ac processes in point-contact junctions.         Millimeter and Submillimeter Wave Radiation Generated by a Josephson Junction    R.K. Elsley and A.J. Sievers Summary: The current in a Josephson junction oscillates at a frequency /spl upsi/ determined by the voltage V across the junction according to the relation h/spl upsi/ = 2eV. The constant of proportionality is 2e/h = 16.1 cm/sup -1//mV or 484 GHz/mV. In addition, radiation impinging on a junction induces a voltage across it, thus mixing the incoming and the Josephson frequencies. These properties indicate that the junctions may be used in the far-infrared as both detectors and sources of radiation.         Mixing with Gain in Josephson Junctions    B.T. Ulrich and T. Lee Summary: Frequency conversion efficiency is calculated analytically for a resistively shunted Josephson junction in which the a.c. Josephson oscillation serves as local oscillator. Effects due to frequency dependent impedances are treated explicitly. Conversion efficiency greater than one can occur; i.e.,mixing with gain is possible in a Josephson junction OScillator-Mixer-preamplifiER (OSMER).         Participants of 1972 Applied Superconductivity Conference    No author information available Summary: Not available         Subject Index (1972)    No author information available Summary: Not available         Author Index (1972)    No author information available Summary: Not available

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