Self-consistent simulation of resistive kink instabilities with runaway electrons

It has been observed in experiments that MHD instabilities can be excited in a post-disruption plasma with large runaway electron current. The instabilities can cause significant loss of runaway electrons to the wall due to stochastic magnetic fields. In this work, we use the MHD code M3D-C1 combining with a fluid model for runaway electrons to simulate the nonlinear evolution of MHD instabilities in the runaway electron final loss event in DIII-D shot 177040. The simulation of relativistic runaway electrons is optimized with a method of characteristics to reduce numerical instabilities and save simulation time. It is found that the dominant MHD instability is a (2,1) resistive kink mode, which can grow within tens of microseconds due to the large resistivity in the post-disruption plasma. Runaway electrons are lost as the stochastic region grows and only a small population near the core can remain. The plasma current converts from runaway electron current to Ohmic current due to the induction electric field, and new current profile is more peaked near the core which can lead to (1,1) kink instability. The deposition area of lost REs on the wall is also calculated. Given the good agreement with experiment, the simulation model provides a reliable tool to study macroscopic plasma instabilities in existence of runaway electron current, and can be used to support future studies of runaway electron mitigation strategies in ITER.