Engineering design status of the KSTAR SC bus-line

The superconducting (SC) bus-line system is for the current transmission between SC coils and current leads. In the Korea Superconducting Tokamak Advanced Research (KSTAR) device, twelve pairs of current transmission lines are required for 16 TF coils and 7 pairs of PF coils. The current transmission lines consist of cable-in-conduit conductors (CICCs), which are square-shaped and use a SS316LN jacket surrounding 324 NbTi strands and 162 copper strands. The CICCs are cooled with supercritical helium. The bus-line system is divided into out-of cryostat bus-lines (OCBs), in-cryostat bus-lines (ICBs), and interface terminals. The OCBs are integrated into two vacuum ducts, which have a diameter of 500 mm and total length of about 60 m. There are intermediate joint sections in the OCBs for the flexibility of assembly. The interface terminals at both ends of the OCBs are to give mechanical and electric connection, with consideration of the thermal contraction. The heat loads of the thermal shields in OCBs are about 680 W in total. The ICBs to extend the SC coil joints to the cryostat boundary are supported with some special-shaped structures and G-10 clamps to compensate for thermal contraction and to restrain against lateral motion and rotations.