Simulation of plateau formation during current quench and MHD instabilities with runaway electrons*

During a 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 module for the M3D-C1 code¹.   This fluid runaway electron model is fully coupled to the bulk plasma.  It utilizes an implicit time advance with sub-cycling that allows runaway velocities approaching the speed of light, c.   Both the Dreicer and avalanche source terms are included, and we have verified their implementation by performing benchmarks with the JOREK code²..   We have computed the linear stability of a runaway electron discharge and compared with an analytic model for a circular cylindrical discharge and verified that low mode number tearing modes acquire a rotation caused by runaway electron-MHD interaction³.  Also, the tearing layer is much narrower in a runaway electron discharge^3,4.   Recent emphasis is on modeling runaway electron plateau formation during mitigation experiments on DIII-D, including the intentional shedding of runaways by lowering the edge safety factor, q(a) to 2.0⁵.

¹S. Jardin, N. Ferraro, J. Chen, et al  J. Comput. Sci. Discovery, 6 014002 (2012)

²V Bandaru, M. Hoelzl, F. Artola et al , Phys. Rev. E, 99, 063317 (2019)

³C. Zhao, C. Liu, S. Jardin, et al, Nuclear Fusion 60 126017 (2021)

⁴C. Liu, C. Zhao, S. Jardin, et al, Phys. Plasmas 27 092507 (2020)

⁵C. Liu, C. Zhao, S. Jardin, et al. “Self-consistent simulation of resistive kink instabilities with runaway electrons”, submitted to Plasma Physics and Controlled Fusion (2021)