HTS Cross-Shaped Strand With Copper Former: Improvement of HTS Quasi-Isotropic Strand for Better Twisting Characteristics

Twisting strain is a main reason that leads to the degradation of the critical current of high temperature superconducting (HTS) quasi-isotropic strand (Q-IS) under torsional loads. In this article, an HTS cross-shaped strand (C-SS) is proposed in order to improve the twisting characteristics of Q-IS. We first simulate and measure the critical current of Q-IS and C-SS under self-field at 77 K. Subsequently, the arrangement direction of REBCO tapes in Q-IS and C-SS that can minimize the twisting strain is analyzed and obtained. Finally, the twisting strain distribution and twisting characteristics of Q-IS and C-SS under different torsional loads are analyzed numerically and experimentally. The results show that the critical current of C-SS is slightly less than that of Q-IS without torsional load. However, the critical current density and magnetic field distribution of C-SS show better isotropic properties than that of Q-IS. When torsional loads are exerted on both strands, C-SS presents better twisting characteristics than Q-IS and its normalized critical current degrades slower than that of Q-IS.