Impact of indentation on the performance of high Jc Nb3Sn strand

Abstract

To meet the peak magnetic field requirements of the central solenoid (CS) and toroidal field (TF) magnets in the China Fusion Engineering Test Reactor (CFETR), cable-in-conduit conductors (CICC) that are composed of Nb3Sn strands with high critical current density (Jc) have been developed. The Short-Twist-Pitch (STP) design is adopted to avoid performance degradation caused by the electromagnetic cycles. But the STP design and tight cabling will cause severe indentation at the contact point between strands. Previous studies on Nb3Sn CICC show that the indentation has a significant effect on the critical current (Ic) and residual resistivity ratio (RRR) of the superconducting strand. Therefore, the same study was carried out for the high Jc Nb3Sn superconducting strand produced by Oxford Superconducting Technology (OST) and Kis wire Advanced Technology CO., Ltd. (KAT). In this paper, the Ic and RRR measurements of sample at different indentation depths were made, and the results were compared with the previous Nb3Sn indentation strands and flat rolled samples. Also, the hysteresis loss of the samples with different indentation depth was measured, and the change of effective filament diameter with indentation depth was obtained.