Cooling and excitation tests of an inner vertical coil for the Large Helical Device

The Large Helical Device (LHD) under construction at NIFS is a nuclear fusion experimental device consisting of two superconducting helical coils and three pairs of poloidal coils. A pair of inner vertical (IV) coils with a combined stored energy of 161 MJ have been delivered to NIFS. They were the 4 m outside diameter coils wound from cable-in-conduit conductors composed of 486 strands with a copper matrix. The authors conducted supercritical helium cooling and excitation tests to confirm the cooling and superconducting characteristics of one of the IV coils before its assembly into the LHD cryostat in 1997. It has been assembled into the SHe test facility at the Toki site of NIFS, and was cooled down and energized to 2.2 kA in February and March 1995. The test facility will be repaired in part, and the coil will be tested to confirm the characteristics at the rated current of 20.8 kA within the year.