Contact resistance of demountable multi-pin joint for superconducting helical coil

We designed an "Inserting Multi-Pin Joint" for a superconductor to realize a demountable superconducting helical coil for the heliotron fusion reactor. The relation between contact resistance and contact pressure was investigated using multi- and single-taper-pin inserting joints. These taper pins were plated with 5∼50μm thick indium. The minimum contact resistance at 7T was 6×10^-9Ωcm²in a single-joint sample and 9×10^-9Ωcm²in a multi-joint with 300MPa contact pressure. This contact resistance ratio of multi-joint to single-joint agreed with the theoretically calculated value. In the reactor model Heliotron F with 3.5GJ magnetic energy, total joule loss due to the contact resistance of the joint was estimated at 4.8kW, which was small in comparison to the total cooling power of about 10.8kW. These results suggest the possibility of applying a tapered pin inserting joint to the superconducting helical coil.