Long-Term Monitoring of Hydraulic Characteristics of LHD Poloidal Coils

We present a fourteen-year data summary of the hydraulic characteristics of the large helical device (LHD) poloidal coils. The superconductors of the poloidal coils are cable-in-conduit conductors (CICC) cooled by circulated supercritical helium. The long-term operation of the LHD demonstrates that the initial hydraulic characteristics can be maintained without flow obstruction. Fine mesh filters installed at the inlet trapped impurities during cool-down of the coils, confirmed by monitoring the pressure drop of the filters. The filters have an important role in removing particles of impurities in the helium and maintaining the hydraulic characteristics of the coils.