Experimental study on the characteristics of current distribution in Rutherford cables and parallel strands

The current distribution in a multi-stranded superconducting cable such as Rutherford cable plays an important role in the stability. Rutherford cables consist of many strands which are twisted and electrically contacted together. Because of this complexity, it is hard to know factors that effect to the current distribution and hence to the stability. The most important factors may be interstrand contact resistances and mutual inductances between strands mainly caused by twisting strands. To evaluate the effect of contacting and twisting, we compared the characteristics of Rutherford cables with parallel strands. We have performed experimental studies on these items for parallel strands with and without insulation by heating with a spot heater. The results for insulated parallel strands show very similar behaviors to those obtained in Rutherford cables. From the fact, we came to the conclusion that the contact resistances at the edges are relatively low in comparison with side-by-side ones between two adjacent strands in the Rutherford cable, and then that the current commutation occurs mainly at the edges. Rest of the transport current could not change the steady state current distribution. To clarify this is remained as a future research.