(TH/P3-15) MHD Simulations for Studies of Disruption Mitigation by High Pressure Noble Gas Injection

Abstract.  The problem of disruptions is a major challenge for ITER which establishes engineering and operational limits. Mitigation of disruptions by high pressure gas injections (HPGI) has been demonstrated experimentally and successfully modeled with the NIMROD code. The role of MHD in cases where impurity penetration is shallow is seen in a series of Alcator C-Mod simulations employing a simple radiation model to cool the tokamak edge with an assumed penetration ranging from well outside to just inside the q=2 surface. Results indicate that this shallow penetration is sufficient to trigger a core thermal quench, and predict a relationship between the delay before the quench onset and the separation between the cooling front and the q=2 surface. In the simulations a 2/1 modes destroys the outer flux surfaces and a 1/1 mode levels the core temperature. The simulations qualitatively reproduce several features of a gas-jet induced thermal quench on C-Mod, but a more sophisticated model is required for a truly predictive code. Improved modeling of the impurities is achieved through the coupling of the 3D NIMROD MHD code and the 0D KPRAD radiation code, to obtain accurate radiation rates and track all charge state populations. Preliminary results from the new code are presented, and comparison is made with C-Mod bolometry data.

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