Performance Comparison of Cables With Partial Transposition

The need of full transposition of the current carrying elements (strands) in large cables is frequently retained as top design criterion for conductors operating in pulsed mode. However, when the transposition error, i.e., the inductance difference among the strands, is small and the inter-strand resistance is low, the criterion can be relaxed for a certain range of operating conditions. In this work, two partly transposed cables made of 18 Nb3Sn strands and one copper core (cu +6 + 12) and 19 Nb3Sn strands (1 + 6 + 12) are assembled in a SULTAN sample and tested under various operating conditions. No significant performance difference is observed, i.e., the 19 strands cable has slightly higher current sharing temperature, T-cs, than the 18 strands cable, as predictable from the superconductor cross section. The inductance imbalance in the 1 + 6 + 12 cable does not lead to either instability or performance loss. The test results support the soundness of the conductor layout of EUROfusion DEMO, where the 19 strands assembly is used as the first cable stage of the react & wind conductor.