Ultra-long pulse operation using lower hybrid waves on the superconducting high field tokamak triam-im

Ultra-long pulse operation (> 3 min) was achieved on the superconducting high field tokamak TRIAM-1M. In this operation, the plasma current was maintained with a relatively peaked current distribution by the 2.45 GHz radiofrequency power (PRF < 35 kW) alone. A stationary plasma with a driven current of up to 35 kA and a line averaged electron density of up to 3 x 1012 cm"3 was produced by precise plasma position and gas feed control. The extremely long discharge showed the interesting characteristics that the high temperatures of about 1 keV for the electrons and about 0.5 keV for the ions were kept almost constant during steady state current drive and that there was no impurity accumulation which could have a fatally adverse effect on steady state tokamak operation.