MHD Simulations for Studies of Disruption Mitigation by High Pressure Noble Gas Injection

The problem of disruptions is a major challenge for ITER which establishes engineering and operational limits. MHD simulations including radiation and atomic physics have the capability of extending results of mitigation experiments on present devices to accurate predictions for ITER. 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 between 1.5 and 3.0 cm. 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. This prediction can be tested experimentally by varying the effective penetration relative to q = 2. 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 that can be extended to ITER. 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. Simulations for several gas species are possible. Preliminary results from the new code are presented, and comparison is made with C-Mod bolometry data.