Recent progress in the superconducting tokamak TRIAM-1M

Extensive studies of a steady-state tokamak reactor have been carried out o n the superconducting tokamak TRIAM-1M. A discharge of (e) over tilde(e) = 2 x 10(18) m(-3) lasting more than 2 h has been demonstrated using a 2.45 G Hz lower hybrid current drive (LHCD). A high-density plasma of ii, = 2 x 10 (19) m(-3) has been sustained for 1 min using a 8.2 GHz LHCD under the high average wall loading of 5 MW m(-2) on the limiter. Recently, a single-null divertor configuration with high elongation (kappa = 1.5) was also success fully maintained for 1 min by the 2.45 GHz LHCD. A transition of the ion te mperature (T-i) from 0.6 keV to about 2.5 keV is observed in 2.45 GHz LHCD plasmas; this operational regime, is called the 'high ion temperature (HIT) ' mode. The 'HIT' mode is characterized by the existence of a steep T-i gra dient (approximate to 50 keV m(-1)) near r/a similar to 0.4. It is found th at the 'HIT' mode appears in a narrow window of the electron density and ho rizontal plasma position. The 'HIT' mode can be successfully maintained for over 1 min with accurate control of the density and position.