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

Abstract

In this paper, an optimization method to determine themagnetic 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. Thenthe Jc(B)-dependence that fits optimally to the measurements is searched for. In thesecomputations the self-field of the sample is taken into account and thereby measurementsperformed in low external magnetic fields, below 0.1 T, can be exploited. Here theJc(B)-dependence of YBCO material is described by the Kim model, which is modified to include theanisotropy also. Thus, there are four parameters to search for: zero field critical current densityJc0, reference fieldB0, Kim model exponentα and anisotropyscaling factor γ. The search for these parameters was computationally challengingbut computation times were still satisfactory. As examples, theJc(B)-dependencesof two YBCO samples from different manufacturers were found. For both samples, all parameters exceptB0 were near each other.For example, Jc0 values forboth samples were about 0.9 × 1010 A m−2.