Research on Disruption and Thermal Quench of Long-Pulse Discharge

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(1) Controllable plasma current density distribution is obtainable by numerical calculation of ray-trace and Fokker-Planck equations. We developed the numerical calculation program and applied it to the 8.2 GHz LHCD plasma. Although the absolute driven current depends on the model of energy gap, the dependence of the driven plasma current profile on the line-averaged electron density coincides the dependence of the profile estimated from the measured hard X-ray profile emitted from high-energy electrons.(2) We measured the impurity density distribution of 8.2 GHz LHCD discharge with multi-channel vacuum ultra violet spectrometer. Molybdenum impurity, which is the material of the poloidal limiter, increases temporally, and results in discharge termination. This phenomenon suggests the thermal quench due to impurity emission cooling and following current disruption.(3) To avoid the impurity increase in the plasma, we made a single-null divertor configuration in the superconducting tokamak TRIAM-1M.Assuming the thermal load profile onto te divertor plate, we calculated 2-dimentional temperature distribution in the divertor plate and the stainless steel supporting plate. By comparing the result with the temperature of the water-cooled stainless steel plate measured by CA thermo-couple, the total thermal load onto the divertor plate was estimated to be 20-35 % of the RF input power.(4) What current profile does a plasma realize in steady state? This problem coincides the problem what confinement is realized in steady state. We studied theoretically on the effect of the current profile on the transport coefficient. And we formulated an element of "profile control research" from the view point of "plasma confinement". According to the formulation, we studied theoretically on the confinement improvement phenomena concerning LHCD and high-beta oriented experiments.