High Power Heating and Steady State Operation in the Large Helical Device

Recent advances in the high power and steady state heating system and experiment results of the Large Helical Device (LHD) are reviewed in this paper. Plasma performance is extended largely through high power NBI, ECH and steady state ICRF heating devices, and improved operation techniques. The NBI of a 28 MW has extended the plasma parameter regime such as ion ITB plasmas, has a central ion temperature of more than 8 keV, and the extremely high-density plasmas ten times higher than the tokamak limit. An ECH system with seven gyrotrons (total power of 4.6MW) has been operated for pre-ionization and plasma heating. The high electron temperature regime was extended toward a higher density regime and a central electron temperature of 13.5 keV was achieved with a line-averaged electron density of n_e = 1 x 10¹⁹ m^-3. Steady state operation plasma with n_e =  1.2 x 10¹⁹ m^-3, ion and electron temperature of 2 keV, and plasma sustainment time of 48 min was achieved with ICH and ECH heating power of 1.2 MW for majority helium with minority hydrogen.