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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
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.
IAEA 2001
