Design, fabrication and commissioning of the KSTAR TF current feeder system

The 16 toroidal field (TF) coils of the Korea Superconducting Tokamak Advanced Research (KSTAR) device are connected in series through inter-coil buses. The 15 inter-coil buses connecting nearby TF coils used the superconducting cable-in-conduit conductor (CICC) that is identical to the conductor of the main TF bus-lines. In addition, two half-turn buses are connected to the remaining two TF coil terminals, and finally routed to the vicinity of the inter-coil buses to minimize the cross-sectional area of the closed loop between inter-coil buses and half-turn buses. Strand-to-strand (STS) joints are utilized to join the TF coil terminals to the end parts of inter-coil buses. The TF current feeder system (CFS) has two pairs of superconducting (SC) bus-lines and current leads. This arrangement has an advantage in the reliable current discharging of SC bus-lines because one half of the current (17.5 kA) flows through each bus-line. In this paper, general design features, manufacturing and operational results of the superconducting TF bus-line are reported in detail, including analysis results for the quench-safety of the half-turn bus.