10 years of engineering and physics achievements by the Large Helical Device project

This article reviews 10 years of engineering and physics achievements by the Large Helical Device (LHD) project with emphasis on the latest results. The LHD is the largest magnetic confinement device among diversified helical systems and employs the world's largest superconducting coils. The cryogenic system has been operated for 50,000h in total without any serious trouble and routinely provides a confining magnetic field up to 2.96T in steady state. The heating capability to date is 23MW of NBI, 2.9MW of ICRF and 2.1MW of ECH. Negative-ion-based ion sources with the accelerating voltage of 180keV are used for a tangential NBI with the power of 16MW. The ICRF system has full steady-state operational capability with 1.6MW. In these 10 years, operational experience as well as a physics database have been accumulated and the advantages of stable and steady-state features have been demonstrated by the combination of advanced engineering and the intrinsic physical advantage of helical systems in LHD. Highlighted physical achievements are high beta (5% at the magnetic field of 0.425T), high density (1.1×1021m−3 at the central temperature of 0.4keV), high ion temperature (Ti of 5.2keV at 1.5×1019m−3), and steady-state operation (3200s with 490kW). These physical parameters have elucidated the potential of net-current free helical plasmas for an attractive fusion reactor. It also should be pointed out that a major part of these engineering and physics achievements is complementary to the tokamak approach and even contributes directly to ITER.