Optimization of Interstrand Coupling Loss and Transverse Load Degradation in ITER $\hbox{Nb}_{3}\hbox{Sn}$ CICCs

Abstract

For the ITER Central Solenoid (CS), with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Nb}_{3}\hbox{Sn}$</tex> </formula> CICCs that operate under fast ramping conditions, the selection of the twist pitch lengths can have a significant impact on the performance. The critical current and temperature margin are influenced by the thermal contraction of the composite materials, the transverse electromagnetic forces, and coupling currents. The numerical cable model JackPot-ACDC is developed to calculate the interstrand coupling loss for any time-dependent current and magnet field for all strand trajectories in a CICC. It was a priori predicted that the amount of coupling loss and critical current degradation is subject to interference due to different subcable twist pitches. Here test results are discussed of the ITER CS conductor sample, manufactured according to the proposed design, optimizing the transverse load degradation, the temperature margin, and the coupling loss.