Assessment of massive gas injection as a disruption mitigation tool in Tore Supra

Abstract

Massive gas injection was used on Tore Supra to study disruption mitigation. The cooling time between the injection and the thermal quench drops to 2ms for larger gas flow rates (∼5e24atoms/s) limiting the radiated energy to ∼10% of the plasma thermal energy content. A significant reduction of the heat load on the limiter is nevertheless observed in the mitigated cases. The broadening factor of the power decay length in the scrape-off layer during the thermal quench estimated around 10 (+/−5) does not change significantly between mitigated and unmitigated. Reached densities with He injections are sufficient to suppress primary runaway electrons (dominant on Tore Supra) but still far too low to avoid avalanche process (dominant in ITER). The extension of the current quench time, which is observed in mitigated disruptions (typically by 50%), could be an attractive feature to reduce the requirements on the density.