Critical current degradation behavior in Bi-2212 round wires under cyclic transverse stress

Abstract

Bi-2212 multi-core round wires without anisotropy can be made into Rutherford cable and cable-in-conduit conductor (CICC) using traditional cable winding technology, which has been widely used in high-field magnets such as fusion reactors. Recently, Bi-2212 is considered to be one of the most promising potential superconducting magnet materials in the Chinese Fusion Engineering Test Reactor (CFETR) magnet. However, Bi-2212’s ceramic structure and Ag/Mg alloy sheath make it susceptible to stress. Due to the complicated working environment of magnet, Bi-2212 round wire is bound to be affected by cyclic electromagnetic stress and thermal stress. Several researchers have reported the performance of Bi-2212 round wire under axial tension strain and tension fatigue. And the impact of indentation on the critical current of Bi2212 round wire has been studied. However, the study of transverse stress characteristics has not been reported. In this work, critical current degradation under cyclic transverse stress for Bi-2212 round wires prepared by different heat treatment processes was studied. The initial critical current Ic0 at 77 K for sample sintered at overpressure with annealing was the highest and Ic0 for sample sintered at atmospheric pressure without annealing was the lowest. The greater transverse fatigue stress will accelerate the process of fatigue.