[en] The objective of this program was to undertake a comprehensive study of the upper critical field Hc₂ of the high-T/sub c/ A15 superconducting compounds. Interest in this problem was occasioned by the availability of new materials preparatory techniques (electron beam coevaporation) that made possible for the first time the preparation of samples in which the relevant material parameters (e.g., composition and order) could be systematically varied. The work involved critical tests of the existing theory, extension of the theory, use of the theory to determine important microscopic material parameters, and development of new principles for the optimization of Hc₂ in practical high-field superconducting conductors. As a result of this program, optimization of the practically important high-field superconductors Nb₃Sn and V₃Ga are proceeding more rationally, fundamental additions to the theory of high-field superconductors have been introduced, and new insights have been obtained regarding the factors governing the high T/sub c/'s of this important class of superconductors

[en] The application of a new superconducting composite wire developed by C. C. Tsuei for high-field, high-current uses is explored. The importance of the discontinuous nature of the superconducting filaments in this material is analyzed. Calculations indicate that practical wire may have a remnant resistivity of 10^-14 ohm-cm or less and experiments to date are reported in which attempts were made to measure this quantity. Observations of quantum coupling between filaments in this wire are also reported

[en] Different types of superconductivity materials and mechanisms of supeconductivity appearance in them are described. Superconductors with heavy electron fermi-liquid (CeCu₂Si₂, UBe₁₃, UPt₃), superconductors with low electron concentration-(Ba(sub(1-x)Pbsub(x))O₃, inorganic superconductors with low grain size (superlattices Nb/Ta, niobium and tantalum trichalcogenides), organic superconductors, superconductors of the A15 type (Nb₃Sn,V₃Si), B1 type (NbN, PdH)-ternary superconductors, amorphous and granulated superconductors, are considered among new ones. Technological applications of the superconducting materials and perspectives of further investigations are briefly characterized

[en] A report is given of research aimed at developing a high current density superconducting power transmission line with low ac losses. Specifically, a study is made of the enhancement of the maximum superconducting current density that can be sustained in Nb₃Sn through formation of fine scale layered composites. Procedures are described which enable fabrication of these composites by electron beam evaporation. In addition, studies on dielectric losses in potential low temperature insulating materials are surveyed. Relevant supplementary information is contained in appendices

[en] The cryogenic engineering and cryogenic materials communities have traditionally been well aware of the problems and opportunities associated with large-scale applications of superconductivity, i.e., those involving high-field, high-current superconductivity such as magnets, generators, power lines, etc. By comparison, appreciation of the so-called small-scale applications of superconductivity -- superconducting electronics -has been much less. However, superconducting electronics is now increasingly emerging as a well-defined technology with considerable technical and economic promise. Major development programs are underway. This paper is concerned with the status of these applications and the major challenges that require engineering solutions and/or science basic to this technology. The basic materials in use are reviewed, as well as the manufacturing technologies for each and the associated problems

[en] The authors present a device concept for a current-controlled variable delay for superconducting transmission line. The device makes use of the change in kinetic inductance of a superconducting transmission line under the application of a DC bias current. The relevant materials parameters and several promising superconducting materials have been identified

[en] We report depth profiling of the critical current density and resistivity of YBa₂Cu₃O_7-x films grown by in situ electron beam evaporation. The method is capable of providing important information on the uniformity of the films, and on the commonly observed property that the critical currents in high temperature superconductor coated conductors do not scale linearly with thickness. Local critical current density shows a clear correlation with local resistivity. Homogeneous transport properties with a large critical current density (4-5 MA/cm² at 77 K, 0 T) are observed in top faulted region while it is found that the bottom part carries little supercurrent with a large local resistivity. Therefore, it is possible that thickness dependence of critical current density is closely related with a topological variation of good superconducting paths and/or grains in the thin film bodies. The information derived from it may be useful in the characterization and optimization of superconducting thin films for electrical power and other applications

[en] This study reviews recent advances in the understanding of the upper critical field (H _c2 ) of real high-field superconductors, and, in particular, addresses the role of disorder in determining H₂ of the A15 superconductors and corrections to the theory of Pauli limiting. Nb₃Sn and V₃Ga are used as the principal test materials. After the theoretical and calculational modes of the study are applied to them, it is concluded 1) that Nb₃Sn and V₃GA are likely to have roughly the same H _c2 (0), although for different reasons, and 2) that if this is true then any applications requiring H _c2 (0)'s larger than 300 K0e will probably require using the metastable A15's: Nb₃A1 (in a well-ordered form), Nb₃ (AlGe), or Nb₃Ge. At this point it would be worthwhile to consider the Chevrel phases where even higher H _c2's have been demonstrated

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No abstract available