Design, development and operation of superconducting system for LHD

The Large Helical Device (LHID) of National Institute for Fusion Science (NIFS) is a heliotron-type experimental fusion device which has the capability of confining current-less and steady-state plasma. The primary feature on the engineering aspect of LHD is using superconducting coils for magnetic confinement: two pool boiling helical coils (H1, H2) and three pairs of forced-flow poloidal coils (IV, IS, OV) wound with cable-in-conduit conductors (CICC). The maximum magnetic field at plasma center is 3 T in the Phase I experiment and 4 T in Phase II, while its stored energy becomes 0.9 GJ and 1.6 GJ, respectively. These coils are connected to the power supplies by superconducting bus-lines with their nominal current of 31.3 kA. The construction of LHD started in 1991 and was completed by the end of 1997. During this period, extensive research and development were conducted to complete a large-scale superconducting system. The plasma experiment started on March 31, 1998 and four plasma experimental campaigns have been performed successfully in three years. The fifth cycle operation started in August 2001. The knowledge which has been acquired during the design, development, and operation of superconducting system for LHD, is summarized.