Simulation of DIII-D disruption process with pellet injection and runaway electrons using M3D-C1 code

During a tokamak disruption, electrons can runaway and be accelerated to high energies, potentially damaging the first wall. To predict the occurrence and consequences of runaway generation during a disruption, we have developed a runaway electron (RE) module for the M3D-C1 code. This fluid RE model is fully coupled to the bulk plasma and pellet model. It utilizes an implicit time advance with sub-cycling that allows runaway velocities approaching the speed of light. Both the Dreicer and avalanche source terms are included, and we have verified their implementation by performing benchmarks with the JOREK code. We have computed the whole non-linear disruption process starting from the beginning of a single pellet injection to the time that runaway electron current plateau has been formed. This process includes both thermal quench and current quench phases with RE beam in disruption. Such a simulation is challenging due to multi-scale physics. M3D-C1 runs for a DIII-D discharge 177053 reveal detailed dynamics of the runaway current density and the electromagnetic field structure, in particular the role of the electric field in the runaway evolution.