How to determine critical current density in YBCO tapes from voltage–current measurements at low magnetic fields

Abstract

In this paper, an optimization method to determine the magnetic field dependence of the intrinsic critical current density, Jc(B), is introduced. First of all the critical current is measured in various external magnetic fields. Then the Jc(B)-dependence that fits optimally to the measurements is searched for. In these computations the self-field of the sample is taken into account and thereby measurements performed in low external magnetic fields, below 0.1 T, can be exploited. Here the Jc(B)-dependence of YBCO material is described by the Kim model, which is modified to include the anisotropy also. Thus, there are four parameters to search for: zero field critical current density Jc0, reference field B0, Kim model exponent α and anisotropy scaling factor γ. The search for these parameters was computationally challenging but computation times were still satisfactory. As examples, the Jc(B)-dependences of two YBCO samples from different manufacturers were found. For both samples, all parameters except B0 were near each other. For example, Jc0 values for both samples were about 0.9 × 1010 A m−2.