AC Losses in Poloidal Coils of the Large Helical Device

AC losses in poloidal coils of the Large Helical Device (LHD) have been measured during single-pulse operations. The superconductors of the coils are Nb-Ti cable-in-conduit conductors (CICC) cooled by supercritical helium. The enthalpy increase due to the losses was observed at the inlet and outlet of the helium coolant. Time constants of the coupling losses can be estimated using analytical expressions with a circuit model and by considering the magnetic field distribution in the coil. The estimated time constants are 80 and 200 ms for two of the poloidal coils. We found a clear difference in the time constants, even though the two coils were fabricated with exactly the same design.