Effect of non-uniform current distribution on the stability in Nb-Ti cable-in-conduit superconducting conductor

Abstract

30kA-NbTi Demo Poloidal Coil (DPC-U) exhibited instability such as the conductor quenches at 40% of the rated current which is still expected conductor critical current, instability was caused by the non-uniform current distribution in the DPC-U conductor whose strands were insulated from each other. To investigate the instability of the DPC-U conductor, a stability experiment of a subsize conductor consisting of 27 strands was performed and the effect of the current imbalance on the stability was investigated. The current imbalance was forcibly established in the conductor using two current sources in this experiment. The experimental results indicate that the stability margin decreases as the current imbalance becomes larger and that the stability margin of the conductor is governed by the stability of the strand with the highest current in the conductor. Also, it is confirmed from the experimental results that the instability of DPC-U has to be attributed to the current imbalance in the conductor.