Abstract
Recent progress of superconducting magnet system design for Large Helical Device (LHD) of National Institute for Fusion Science (NIFS) is described. LHD is one of large scale nuclear fusion devices which will be completed in the 20th century, and fully superconducting coil system to create magnetic field. LHD is composed of a plasma vacuum vessel, superconducting helical and poloidal coils, cryogenic supporting structures, and an outer vacuum vessel, and surrounded by utilities of coil power supply, helium refrigerator and nitrogen supply, and vacuum pumping system. Cryogenic mass of the system is estimated as 860tons including coil and supporting structure. Cooling method of the superconducting coil is decided as bath cooled of liquid helium for the helical coil, and force cooled of supercritical helium for the poloidal coil. Major and minor radii of the helical coil are 3.9m and 0.975m, respectively. The conductor material of Nb-Ti alloy is used for both helical and poloidal coils from the point of strain effect. Conductor maximum field will be 6.9T for the plasma center field of 3T at the first phase with saturated boiling helium and 9.2T for 4T at the second phase with superfluid helium, Electromagnetic force and electrical insulation of the coil are the most important items to design the coil. Research and development work is intensively continued now, including conductor stability, helical and poloidal winding, elasticity of the coil, and cryogenic handling.
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