First predictive simulations for deuterium shattered pellet injection in ASDEX Upgrade

Abstract

First simulations of deuterium shattered pellet injection into an ASDEX Upgrade H-Mode plasma with the JOREK MHD code are presented. Resistivity is increased by one order of magnitude in most simulations to reduce computational costs and allow for extensive parameter scans. The effect of various physical parameters on MHD activity and thermal quench (TQ) dynamics is studied and MHD influence on ablation is shown. TQs are obtained quickly after injection in most simulations with a typical duration of 100 microseconds, which slows down at lower resistivity. Although the n = 1 magnetic perturbation dominates in the simulations, toroidal harmonics up to n = 10 contribute to stochastization and stochastic transport in the plasma core. The post-TQ density profile remains hollow for a few hundred microseconds. However, when flux surfaces re-form around the magnetic axis, the density becomes monotonic, again, suggesting beneficial behavior for runaway electron avoidance/mitigation. With 1021 atoms injected, TQ is typically incomplete and triggered when the shards reach the q = 2 rational surface. At a larger number of injected atoms, TQ can set in even before the shards reach this surface. For low field side injection considered here, repeated formation of outward convection cells is observed in the ablation region reducing material assimilation. This is due to sudden rise of pressure in the high density cloud when the stochastic region expands further releasing heat from the hot core. After TQ, strong sheared poloidal rotation is created by Maxwell stress, which contributes to re-formation of flux surfaces.