Development of KORC-NIMROD couplings toward hybrid kinetic-fluid runaway electron mitigation modeling

Unmitigated runaway electrons (REs) threaten the achievable performance in ITER, and there is a pressing need for predictive modeling of RE mitigation via shattered pellet injection. In the post-disruption phase, most of the current is carried by the REs instead of the cold, background plasma. Modeling needs to evolve the full distribution function for the kinetic REs self-consistently with a magnetohydrodynamic (MHD) model for the background plasma. This work presents advances and plans for the implicit coupling of the Kinetic Orbit Runaway electrons Code (KORC) with the nonlinear MHD code NIMROD. For the NIMROD to KORC one-way coupling, we are building upon NIMROD’s RE tracer orbits [1] to incorporate the optimized particle-pushers and robust collision operators developed in KORC [2], which include Fokker-Planck and large-angle collision operators that account for partially-ionized impurities. To couple back KORC to NIMROD, we calculate the fluid RE current using a previously developed PIC scheme [3] to deposit REs onto NIMROD’s finite element grid.

[1] Izzo et al., Nucl. Fusion 51, 063032 (2011)

[2] Beidler et al., Phys. Plasmas 27, 112507 (2020)

[3] Kim et al., Comput. Phys. Comm. 164, 448 (2004)