Recent progress on high performance steady state plasmas in the superconducting tokamak TRIAM-1M

An overview of TRIAM-1M experiments is presented. The current status of iss ues related to steady state operation is presented with reference to the ac hievement of super-ultra-long tokamak discharges sustained by LHCD for over 2 h. The importance of control of the initial phase of the plasma, the avo idance of high heat load concentration, wall conditioning and the avoidance of abrupt termination of long discharges are discussed as the crucial issu es for the achievement of steady state operation of the tokamak. A high ion temperature (HIT) discharge fully sustained by 2.45 GHz LHCD with both hig h ion temperature and steep temperature gradient was successfully demonstra ted for longer than 1 min in the limiter configuration. The HIT discharges can be obtained in a narrow window of density and position. The avoidance o f heat load concentration on a limiter is the key point for the achievement and long sustainment of the KIT discharge. As the effective thermal insula tion between the wall and the plasma is improved for the single null config uration, HIT discharges with peak ion temperature > 5 keV and a steeper tem perature gradient of up to 85 keV/m can be achieved through the fine contro l of density and position. Plasmas with high kappa approximate to 1.5 can a lso be demonstrated for longer than 1 min. The current profile is also well controlled for a time about 2 orders of magnitude longer than the current diffusion time using combined LHCD. The serious damage to the material of t he first wall caused by energetic neutral particles produced by charge exch ange is also described. As the neutral particles cannot be affected by a ma gnetic field, this damage by neutral particles must be prevented by a new t echnique.