Accurate determination of the critical state in anisotropic superconductors from transport measurements

Abstract

A method to accurately determine the critical state and the field profile inside an anisotropic superconductor is presented, in which the self-field effect is eliminated. A transport current at its critical value is passing along a slablike superconductor connected in series and placed between two copper slabs of exactly the same cross section. The perpendicular component of the self-field at the edges of the highly textured superconducting sample is compensated by the field produced by the copper slabs and a uniform magnetic field results parallel to the surface of the sample and to the a−b planes of the superconducting grains. This configuration allows the true critical current along the a−b planes to be measured as a function of the magnetic field aligned purely parallel to the a−b planes throughout the sample width. Furthermore, features of the critical state can be deduced from the field dependence of the critical current without using any fitting routines. In particular, when the critical state is anisotropic, as in the case of a highly textured oxide superconductor with the a−b planes parallel to the slab surface, this configuration allows the critical current density along the a−b planes to be measured as a function of magnetic field aligned purely parallel to the a−b planes.

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