Development Of A Cryogenic System For The Large Helical Device

The construction and the cooling schemes of the cryogenic system for the Large Helical Device (LHD) are reported. The LHD is the first fully superconducting heliotron type experimental fusion device, which is under construction at the National Institute for Fusion Science (NIFS). The cryogenic system for the LHD consists of the helium refrigerator, the superconducting helical and poloidal coils and the peripheral equipment, such as superconducting bus-lines, control-valve-boxes and cryogenic transfer-lines. Three different cooling schemes are utilized for each cooling object; a pool bailing for the helical coils, a forced flow supercritical helium for the poloidal coils, a forced flow two phase helium for the coil supporting structure and the superconducting bus-lines. Many technical know-how were applied to develop the complicated cryogenic system for the LHD, which we could gather during the engineering research and developments such as the single coil test of the IV poloidal coil, the development and tests of the full-scale model of superconducting bus-lines and the test operation of the helium refrigerator with a dummy load apparatus.