Present status of design and manufacture of the superconducting magnets for the Large Helical Device

The Large Helical Device (LHD) is a nuclear fusion experimental device with superconducting magnets. Manufacture of the cryostat, the inner vertical coils, and the helical-coil winding machine are now being carried out. Designs for constructing two helical coils and two other pairs of poloidal coils are in progress. The outside diameter of the torus-shaped cryostat is 13.5 m. There are two operational stages for the LHD. Phase I and Phase II. The helical coils will have a magnetic energy of 1.6 GJ and an overall current density of 53 A/mm/sup 2/ in Phase II. The rated current is 13.0 kA in Phase I, and the maximum magnetic field in the helical coil winding in Phase I was calculated to be 6.9 T. Three pairs of poloidal coils are cooled by forced-flow supercritical helium because of the necessity of having no metal coil vessel. The rated current of one inner vertical (IV) poloidal coil is 20.8 kA, and its stored energy is 80 MJ. The maximum magnetic field of the two IV coils was calculated to be 5.8 T. The type of superconductor for the IV coils is a cable-in-conduit conductor.<>