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This work supported by the Air Force Office of Scientific Research.

Limits to the Critical Current in Bi 2 Sr 2 Ca 2 Cu 3 O x Tape Conductors: The parallel path model.

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This work supported by the Air Force Office of Scientific Research.

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  1. Limits to the Critical Current in Bi2Sr2Ca2Cu3Ox Tape Conductors: The parallel path model Bi2Sr2Ca2Cu3Ox (Bi-2223) tapes are currently the preferred conductor for large scale superconducting applications based on high-temperature superconductors. The design of applications and a further development of Bi-2223 tapes require a detailed understanding of current flow in these conductors and an understanding of the relation between the various dissipation mechanisms and for instance temperature and magnetic field. Here we present a parallel path model that describes how a superconducting current in Bi-2223 tapes runs in two distinct paths in parallel. One of the current paths is formed by grains that are connected at angles below 4º. Dissipation in this so-called strongly-linked backbone occurs within the grains and can be described by classical flux creep theory. The other current path, the weakly-linked network, is formed by superconducting grains that are connected at intermediate angles (4º-8º), where dissipation occurs at the grain boundaries. Grain boundary dissipation in this current path does not occur through Josephson weak links, but is strongly related to classical flux creep. We present the result of several experiments obtained on Bi-2223 tapes and single-grained powders that strongly support the parallel path model. For the first time, the critical current density of Bi2Sr2Ca2Cu3Ox tapes can be scaled as a function of magnetic field angle over the entire temperature range from 15 K to 77 K, by use of the parallel path model. Critical current density as a function of magnetic field of a Bi-2223 tape (closed symbols) and the powder extracted from the tape (open symbols) at various temperatures. Dissipation in Bi-2223 tapes and powder at high magnetic field occurs within the grains. D.C. van der Laan, H.J.N. van Eck, B. ten Haken, M. Dhallé and J. Schwartz,to be submitted to Phys. Rev. B (2007) This work supported by the Air Force Office of Scientific Research.

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