Development of a coupled kinetic-MHD equilibrium solver for modeling a post-disruption runaway electron beam

Modeling a post-disruption runaway electron (RE) beam is critical to securing the walls of existing and future high-current tokamaks, including ITER. This work couples the Kinetic Orbit Runaway electron Code (KORC) [1] with the MHD equilibrium solver of NIMROD [2], resulting in a kinetic-RE-MHD hybrid quasi-static state that accounts for collisional damping against impurities, toroidal loop voltage RE acceleration, and an avalanche RE generation source. A RE beam is initialized consistent with a reconstructed DIII-D current profile using a Metropolis-Hastings method adapted from KORC. RE drift and magnetization parallel currents are computed via a guiding center orbit-averaging technique by sampling at regular kinetic time steps. The RE parallel current is subsequently transformed to NIMROD’s finite element (FE) basis by a weighted deposition scheme onto the FE mesh. An iterative resampling technique ensures a quasi-static RE distribution consistent with the MHD current profile. This framework sets the stage for the time-dependent two-way coupling of KORC and NIMROD.

[1] M.T. Beidler et al., Phys. Plasmas 27, 112507 (2020)

[2] E. C. Howell and C.R. Sovinec, Computer Phys. Communications 185, 1415 (2014)