Estimation of Jc(B) dependence from self-field alternating current (AC) losses measured on Bi-2223/Ag tapes

Transport AC losses measured in self-field conditions on multifilamentary Bi-2223 tapes are often found to be lower than those calculated within the framework of the critical state model for a bulk win with elliptical cross section, though generally higher than predicted for a strip. This effect is sometimes ascribed to the non-ideal geometry of the tapes, which does not exactly reproduce either shape. Here we propose an alternative explanation assuming that the critical current density of superconducting material depends on magnetic field. In practice, we analyzed the AC loss curve and deduced different I-c values for the individual data points, using the standard Norris equation for elliptical conductor. This gives the relation between 'calculated' I-c and the self-field associated to AC transport current, which can be regarded as an alternative way to qualify the dependence of J(c) on magnetic field. Important is that this procedure covers the range of fields below the self-field at I-c where the measurement in background DC field can not be used to determine J(c)(B). (C) 1998 Elsevier Science B.V. All rights reserved.