MGI in plasmas with locked modes

Le résumé fourni par la source

Massive gas injection (MGI) is foreseen as mitigation technique for ITER disruptions. Typically, MGI experiments have been carried out by injecting impurity gas in an Hmode plasma, in order to have a target plasma with pre-defined parameters and to test the capability of the plasma in radiating a large amount of energy. Nevertheless MGI will be used in ITER in plasmas with a high probability of disrupting and therefore likely with large non-rotating modes. A series of plasmas with locked modes (LMs) were shut down by MGI, in order to study the influence of these modes on fuelling efficiency and radiation asymmetry. Plasmas with LMs were obtained by increasing the density up to the Greenwald limit; the amplitude of the n=1 radial magnetic field, measured by a pair of saddle coils, was then used to trigger the MGI valves. The presence of LMs is found to decrease significantly the assimilation time of the gas and the amount of gas assimilated up to the thermal quench, decreasing further the already small fuelling efficiency. Moreover, the position of the LM was controlled by applying an n=1 radial magnetic field with the RMP coils. This allowed to choose the gas injection location with respect to the toroidal phase of the mode. Simulations with the NIMROD code (*) have pointed out a possible dependence of gas assimilation efficiency and radiation asymmetry on the relative location of gas injection footprint and mode phase. This contribution will discuss the experimental findings related to these and other simulations. (*) V. Izzo, Impurity Mixing in Massive-Gas-Injection Simulations of DIII-D, TH/P3-13 contribution to the 24th Fusion Energy Conference, 8-13.10.2012, San Diego (USA) 40 EPS Conference on Plasma Physics O5.104

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.