Hysteresis Loss in Poloidal Coils of the Large Helical Device

Abstract

Hysteresis loss in poloidal coils of the Large Helical Device (LHD) has been measured during single-pulse operation. The superconductors of the coils are Nb-Ti cable-in-conduit conductors (CICC) cooled by forcedflow supercritical helium. The loss was measured by monitoring the enthalpy increase of the helium coolant between the inlet and outlet. Although the hysteresis loss was extracted by extrapolating several data sets from pulse excitations with different sweep rates, the extrapolated loss was much larger than the estimation using the magnetic hysteresis of the conductor. The anomalous increase in the loss is likely due to inter-strand coupling loss with long time constants from the order of 10 to 1000 s. The calculations show that the additional coupling loss behaves like a hysteresis loss.

Lessons learned from twenty-year operation of the Large Helical Device poloidal coils made from cable-in-conduit conductors

“…The data for the IS coils are also omitted because the power loss is much lower than that for the OV and IV coils, and sufficient measurement accuracy was not obtained. The calculation shows that the loss may include a hysteresis loss of 10.6 kJ and 7.5 kJ for the OV and IV coils, respectively [4]. The remaining loss corresponds to interfilament and interstrand coupling losses.…”