(EX/4-4) Influence of plasma opacity on current decay after disruptions in tokamaks
1) NFI, RRC ``Kurchatov Institute", Moscow, Russian Federation
2)D.V. Efremov Institute of Electrophysical Apparatus, St-Petersburg, Russian Federation
Abstract. Current decays after disruptions as well as noble gas injections in tokamak are examined. KPRAD model of [D.G. Whyte, T.C. Jernigan, D.A. Humphreys, A.W. Hyatt et al., Journal of Nuclear Materials 313-316 (2003) 1239] is used as a basic one. In addition, opacity effects are included in accordance. Zero dimensional problem is analyzed. The thermal balance determined by Ohmic heating and radiative losses is supposed. As it is shown, the cooled plasmas at the stage of current decay are opaque for radiation in lines giving the main impact into total thermal losses. Impurity distribution over ionization states is calculated from the time-dependent set of equations. Opacity effects are found to be important for all cases examined. The opacity effects are found to be most important for simulation of JET disruption experiments with beryllium seeded plasmas. Using the coronal model for radiation one can find jumps in temperature and extremely short decay times. If one take into account opacity effects, current calculated decays smoothly in agreement with JET experiments. The decay times are also close to the experimental values. Current decay in argon seeded and carbon seeded plasmas for ITER parameters are simulated. The temperature after thermal quench is shown to be twice higher in comparison with the coronal model.
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