Extended MHD Modeling of Disruption Mitigation in SPARC and NSTX-U

Reactor-scale tokamaks must be designed to withstand the large forces and thermal loads associated with disruptions. To characterize these forces and loads, fully three-dimensional magnetohydrodynamic (MHD) simulations of mitigated and unmitigated disruptions in NSTX, NSTX-U, and SPARC model discharges have been performed using the M3D-C1 extended-MHD code. In these simulations, whether mitigated or unmitigated, the thermal quench ultimately proceeds from magnetohydrodynamic instabilities in the current sheet that forms as the edge of the plasma cools, consistent with previous calculations. In the SPARC simulations, poloidally and toroidally localized gas injection sources are included in order to calculate the spatial distribution of radiation on the plasma facing components. Ionization, recombination, and radiation from injected gas is calculated self-consistently with the MHD evolution using a coronal non-equilibrium model based on KPRAD. M3D-C1 implements spatially resolved models of the first wall, vacuum vessel, and passive plates to calculate halo currents and eddy currents. Ports are treated as regions of anisotropic resistivity in an axisymmetric model of the vessel.