Effects of critical current inhomogeneity in long high-temperature superconducting tapeson the self-field loss, studied by means of numerical analysis

Abstract

The effect of the local critical current on the self-field loss in single tapes and multi-paralleltapes is investigated computationally. Generally, the self-AC loss of a superconductorcan be described using the Norris equation based on Bean’s critical state modelwith elliptical, circular or strip cross-sections. However, because of its intrinsiccharacteristics, the critical current of high-temperature superconducting (HTS)tape is inhomogeneous. It is reasonable to expect the local critical currents tohave a Gaussian statistical distribution, according to the central limit theorem; adetailed analysis of self-AC loss is made to develop an interesting calculationprocedure for both single tapes and multi-parallel tapes. The results show that theinhomogeneity of local critical currents has an important effect on the self-field loss. One ofthe goals in this paper is to provide an accurate method for estimating quality,or what level of critical current inhomogeneity in HTS tape is permissible inpractical application. As manufacturing processes are refined through powder in tubeand coating technologies, and the sources of extrinsic macroscopic defects aredecreased, electromagnetic and mechanical performances of Bi2223 and YBCO tapesare greatly improved. Nevertheless, intrinsic microscopic defects such as weaklinks, microcracks and small second-phase formations still exist in the tapes,which will lead to statistically local critical current variations. Therefore, it isvery important to study the effect that variation in local critical currents mayhave on the self-field losses of practical long single and multi-parallel HTS tapes.