Current Sharing and Critical Current Distribution in Bi-2223 Tapes

For the applications of technical superconductors, for example in superconducting high-field or NMR magnets, a detailed knowledge of the superconducting-to-normal transition is essential. Usually, this transition is described by a power law leading to the critical current, I_C, and the n-value. I_C and n are global variables which ignore the microstructure of a superconductor. In contrast, the assumption of a distribution of local critical currents provides a statistical approach to the superconducting-to-normal transition taking into account the non-uniformity of the material. In this paper, the model of local critical currents is applied to describe the measured voltage-current characteristics of the superconducting transition for several types of Bi-2223 tapes. The probability density of the distribution is evaluated and in addition the current sharing occurring in the transition region between the superconducting phase and the matrix material of the composite is discussed.