Analyses for inter-strand coupling loss in multi-strand superconducting cable with distributed contact resistance between strands

Abstract

Multi-strand superconducting cables are utilized to large superconducting machines and/or alternative or pulse current ones, such as fusion machines and superconducting magnetic energy storages (SMESs). We have been studying for electromagnetic phenomena in multi-strand superconducting cables by using both analytical and experimental methods aiming at such large-scale applications. When we are going to evaluate alternating current (AC) loss numerically, especially inter-strand coupling loss, it is important to establish the model of crossover contact resistance distribution between strands and/or sub-cables. For the cable with multiple cabling stages, the contact resistances between two strands (or two sub-cables) change drastically due to the traces of them. They contact well each other at the places where they are crossover. On the other hand, when they are separated, there is no direct contact between them. The relation between AC loss and DC contact resistance was evaluated for a short sample, which is a 3×3 cable with Cr plated Nb 3Sn strands. The AC loss was measured by the calorie metric method at LHe temperature. The contact resistances between two strands were also measured for the same sample in the same condition. Adapting measured contact resistance distribution to the numerical model, the AC loss calculation was fulfilled by using the distributed constant electric circuit. Comparing the calculated loss with the measured one, the modeling method of the contact resistance distribution was modified suitably. Finally the relation between the inter-strand coupling loss and the contact resistance distribution were discussed from the viewpoint of construction of the cable.