Simulation of main chamber wall temperature rise resulting from massive neon gas injection shutdown of ITER

Abstract

Simulations were performed to estimate the main chamber wall heating in ITER resulting from rapid discharge shutdown by neon massive gas injection (MGI). The TokSys current diffusion model coupled with a simplified impurity transport model was used. Impurity parallel flow was treated with a single-fluid pressure-driven flow model. Impurity cross-field diffusion was treated with an empirical diffusion coefficient estimated from present experiments, while impurity poloidal rotation was included empirically by extrapolation in minor radius from present experiments to ITER. For single-valve neon MGI, maximum wall temperatures of order 1100 K are predicted, somewhat below the melting temperature of beryllium (1560 K). Lower temperature excursions were obtained by increasing the number of gas valves, while higher wall temperatures could be obtained by turning up initial plasma thermal energy or cross-field transport coefficients. Highest wall temperatures tended to occur on the centre post during the start of the current quench phase, consistent with present experiments. These results suggest that a single port may be sufficient for safely initiating rapid shutdown in ITER, leaving other ports free for subsequent rapid shutdown tasks such as runaway electron mitigation.