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(OV2/3) Recent Progresses on High Performance Steady-State Plasmas in the Superconducting Tokamak TRIAM-1M

   
S. Itoh , K. Sato , K. Nakamura , H. Zushi , M. Sakamoto , K. Hanada , E. Jotaki , K. Makino , S. Kawasaki , H. Nakashima , and N. Yoshida 
 
Advanced Fusion Research Center, Research Institute for Applied Mechanics, Kyushu University 87, Kasuga, Fukuoka, 816-8580, JAPAN

Abstract
The overview of TRIAM-1M  experiments is described. The up-to-date issues for steady-state operation  are presented through the experience of the achievement of super ultra long tokamak discharges (SULD) sustained by lower hybrid current drive  (LHCD) over 2 hours. The importance of the control of an initial phase of plasma, the avoidance of the concentration of huge heat load , the wall conditioning, and abrupt stop of the long discharges are proposed as the indispensable issues for the achievement of the steady-state operation of tokamak. A high ion temperature (HIT) discharge fully sustained by 2.45 GHz LHCD with both high ion temperature and steep temperature gradient is successfully demonstrated for longer than 1 min in the limiter  configuration. The HIT discharges can be obtained in the narrow window of density and position. Moreover, the avoidance of the concentration of heat load on a limiter is the key point for the achievement and its long sustainment. As the effective thermal insulation between the wall and the plasma is improved on the single null configuration, HIT discharges with peak ion temperature $>$ 5keV and steeper gradient up to 85 keV/m can be achieved by the exquisite control of density and position. The plasmas with high $\kappa \sim 1.5$ can be also demonstrated for longer than 1 min. The current profile is also well-controlled for about 2 orders in magnitude longer than the current diffusion time using combined LHCD. The serious damage to the material of the first wall  caused by energetic neutral particles produced via charge exchange  process is also described. As the neutral particles cannot be affected by magnetic field, this damage by neutral particles must be avoided by the new technique.

     

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IAEA 1999