Internally cooled cable superconductor (ICCS) for TF and PF coils of FED

Abstract

Internally Cooled Cable Superconductor (ICCS) concepts developed for TF and PF coils of FED are described. These concepts represent one of the options for FED, and other conductor concepts are still being explored, i.e., no decision has been made for the conductor concepts to be utilized for FED. The TF coil conductor design is based on an ICCS successfully used in a small test magnet at ORNL. The conductor consists of triplets of NbTi strands loosely packed in a stainless steel conduit similar to the Westinghouse LCP coil. The operating current for the conductor is 25.5 kA at 10 T and 3.1 K. The conductor is co-wound with a stainless steel C-shaped channel to provide a direct load path to the coil case for the accumulated magnetic loads in the winding. The strand diameter in the conducter is optimized to reduce the eddy current losses. The nuclear heating in the winding is the most dominant heat load. In order to remove these heat loads due to nuclear heating and ac losses in the winding, it is necessary to lower the inlet temperature of helium to 2.2 K. The conductor has a thermal capacity of ∼200 mJ/cc, which provides a comfortable stability margin under the operating conditions. The PF conductor is similar to the TF conductor, but it is modified to meet the requirements of the PF coils. For this conductor, the superconducting filament diameter has been reduced and cupro-nickel barrier is provided between adjacent filaments for reducing the hyteresis and coupling ac losses, respectively, under relatively higher pulsed fields. The conductor is designed to carry 21.3 kA at 8 T and 4.5 K.