Numerical Analyses of Non-Uniform Current Distribution Within the Multi-Strand Superconducting Cable for Fusion Apparatus

Abstract

Multi-strand superconducting cables, e.g., cable in conduit conductors (CICCs), are applied to large-scale apparatus, such as fusion machines. In this sort of cable, strands carry different currents. This phenomenon is known as nonuniform current distribution (NUCD). NUCD causes increase of AC loss and/or instability of the cable. During the energization, induced voltage occurs along each strand and the minute difference between induced voltages results in the circulation current through the closed circuit composed of two different strands. Superposing these circulation currents and transport one, NUCD appears. The leakage inductance along the pair of strands is around 10/sup -7/, thus the minute difference between induced voltages can produce large circulation currents. In spite of this fact, conventional NUCD simulations are fulfilled with ideal circuit models. Here, the ideal model consists of superposition of sinusoidally waving tracks of the strands. We made a numerical electric circuit model based on real tracks of strands simulating actual multi-strand cable. We considered mechanical interactions between the strands and proposed the solution about the strands' positions based on the mechanical energy minimum principle. Establishing suitable circuit model, we successfully calculated NUCD. Finally, NUCD due to the deformation of the cable's cross section was discussed. The deformation is caused by the electromagnetic force or cross sectional forming into rectangular shape.