Results on the superconducting magnet system for the Large Helical Device

The Large Helical Device (LHD) is a plasma physics experimental device with eight superconducting coils. Design and construction of LHD started in April 1990. The trial operation and the first plasma discharge of the eight-year Phase I project for LHD were finished on the last day of March 1998 as initially planned. The second experimental campaign and several excitation tests were conducted from August 1998 to January 1999. Major test results on the superconducting magnet system for LHD are as follows: (1) The cooldown time of the LHD coils and support structure was 23 days. The LHD cryogenic system succeeded in 6400-hour operation and proved its high reliability. (2) Although the inside coil lead and the inner block of one helical coil caused two-stage successive normal propagation at a helical current of 11.45 kA, they were energized to the same current in the superconducting state in the next excitation test. (3) All six poloidal coils were excited stably. (4) Nine flexible superconducting bus-lines with a total length of 497 m were operated stably and safely. In the third experimental campaign many plasma discharge tests up to a plasma field of 2.9 T were carried out.