GOAL AND ACHIEVEMENTS OF LARGE HELICAL DEVICE PROJECT

The Large Helical Device (LHD) is a heliotron-type device employing large-scale superconducting magnets to enable advanced studies of net-current-free plasmas. The major goal of the LHD experiment is to demonstrate the high performance of helical plasmas in a reactor-relevant plasma regime. Engineering achievements and operational experience greatly contribute to the technological basis for a fusion energy reactor. Thorough exploration for scientific and systematic understanding of the physics in the LHD is an important step to a helical fusion reactor. In the 12 years since the initial operation, the physics database as well as operational experience has been accumulated, and the advantages of stable and steady-state features have been demonstrated by the combination of advanced engineering and the intrinsic physical advantages of helical systems in the LHD. The cryogenic system has been operated for 56000 h in total without any serious trouble and routinely provides a confining magnetic field up to 2.96 T in steady state. The heating capability to date is 23 MW of neutral beam injection, 3 MW of ion cyclotron resonance frequency, and 2.5 MW of electron cyclotron resonance heating. Highlighted physical achievements are high beta (5.1%), high density (1.2 x 10(21) m(-3)), and steady-state operation (3200 s with 490 kW).