Numerical modelling of current non-uniformity in braided stacks of tapes

The performance of REBCO multi-stack cables is crucial for next-generation high-field fusion magnets, it is often limited by uneven current distribution. This study employs a 3D finite-element model based on the weak form of the H-formulation to analyze current non-uniformity within a novel BRAided Stacks of Tapes (BRAST) assembly. The model rigorously accounts for the nonlinear E–J power law of the REBCO material, as well as the effects of inter-tape and terminal resistances. The model’s accuracy is verified experimentally. Simulation results establish a clear hierarchy of stability drivers. First, non-uniform terminal resistance determines the inter- tape current imbalance. Low inter-tape contact resistance has a dual role: it amplifies short-range current imbalances at the cable entry point, leading to increased local current loading, while simultaneously promoting a more uniform longitudinal current distribution within the cable, thereby mitigating current inhomogeneity. Furthermore, the analysis reveals that tape regions with reduced critical current can be the onset of overall stack transition, and that the overall stability of the cable is determined by the minimum current-carrying capacity within the tape stack. This study provides quantitative guidance for controlling terminal resistance uniformity and optimizing contact resistance, thereby improving the stability and robustness of BRAST and similar multi- tape superconducting cable systems.