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

The effect of the local critical current on the self-field loss in single tapes and multi-parallel tapes is investigated computationally. Generally, the self-AC loss of a superconductor can be described using the Norris equation based on Bean's critical state model with elliptical, circular or strip cross-sections. However, because of its intrinsic characteristics, the critical current of high-temperature superconducting (HTS) tape is inhomogeneous. It is reasonable to expect the local critical currents to have a Gaussian statistical distribution, according to the central limit theorem; a detailed analysis of self-AC loss is made to develop an interesting calculation procedure for both single tapes and multi-parallel tapes. The results show that the inhomogeneity of local critical currents has an important effect on the self-field loss. One of the 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 in practical application. As manufacturing processes are refined through powder in tube and coating technologies, and the sources of extrinsic macroscopic defects are decreased, electromagnetic and mechanical performances of Bi2223 and YBCO tapes are greatly improved. Nevertheless, intrinsic microscopic defects such as weak links, microcracks and small second-phase formations still exist in the tapes, which will lead to statistically local critical current variations. Therefore, it is very important to study the effect that variation in local critical currents may have on the self-field losses of practical long single and multi-parallel HTS tapes.