Coupling losses in cable-in-conduit conductors for LHD poloidal coils

Coupling losses in Large Helical Device (LHD) poloidal coils have been measured during operations with three different waveforms. The superconductors of the poloidal coils are cable-in-conduit conductors (CICC) cooled by supercritical helium. In the experiments, the operating currents were simultaneously changed with a given waveform, and the enthalpy increase due to the losses was observed at the inlet and outlet of the helium coolant. Inter-strand coupling currents through resistive contact points mainly caused the losses. Time constants of the coupling currents are estimated by using analytical expressions with a circuit model. The results indicate a broad distribution of the time constants from the order of 10–1000 s.