Numerical analysis of the mechanical and electrical properties of CORC cables under torsional loading

The type II high-temperature superconducting (HTS) ReBCO tapes have been widely used in high-field magnets. Conductors on round core (CORC) cables can carry very high currents in background magnetic fields exceeding 20 T, making it one of the most important types of HTS cables. However, the cables of the magnets in the fusion reactor are subjected to large mechanical and electromagnetic loads that may twist the CORC cables. The intrinsic strain of the superconducting cable is constrained by the brittleness of the HTS tape, which, if exceeded, will cause irreversible damage by producing cracks in the ReBCO layer. A finite element (FE) model was developed to predict how the CORC cable will perform in torsional cases. A comparison of numerical simulations with experiments for a single- and double-layer CORC cable is first performed to validate the model's reliability. For single-layer CORC cables, our model reduces the error between FE results and experiments from 46.7% to 6.7%. Variations in the winding angle, tape width, Poisson's ratio of the CORC cable core material, and core radius were made as part of the parametric analysis. The critical torsion angle is analyzed from the perspective of critical current density reduction. The results show that maintaining a small tape gap (smaller winding angle (26−30°), smaller core diameter, and larger tape width) and a small Poisson ratio can improve the strain limit of the ReBCO layer. The reason for the plateau phenomenon in the normalized critical current density curve of the double-layer CORC cable is reinterpreted. It is also confirmed that multi-layer CORC cables still need to maintain a small tape gap. The FE model can guide optimizing a cable design for specific application conditions.