3D Disruption Mitigation Modeling with M3D-C1*

Future tokamaks will require robust disruption-mitigation techniques, the most promising of which use impurity injection to radiate stored energy. We simulate pellet mitigation using the M3D-C1 extended-MHD code coupled to the KPRAD ionization/radiation code. Three-dimensional, nonlinear modeling shows that, with an axisymmetric, on-axis impurity source, the plasma remains stable throughout the thermal quench. Increased resistivity on-axis causes plasma current to diffuse into a thin shell. This shell eventually goes unstable, resulting in a pronounced current spike, the first seen of its magnitude in 3D MHD disruption modeling. Results of a 3D, nonlinear benchmark with NIMROD simulations will be presented. Simulations with a moving, ablating pellet will also be presented, with particular focus on the effect of increased toroidal localization of the deposited impurities. Results will be validated against DIII-D shattered-pellet-injection (SPI) experiments. Finally, we will present progress on using more-sophisticated pellet models, including multiple impurity sources (for multiple toroidal injection and/or SPI modeling) and coupling to a Lagrangian particle code for pellet ablation.