Initialization of a runaway electron beam in a kinetic-MHD equilibrium state*

We combine the Kinetic Orbit Runaway electron Code (KORC) with NIMROD's MHD equilibrium solver to develop a kinetic-RE-MHD hybrid model for analyzing post-disruption runaway electron beams in tokamaks, essential for preserving ITER's wall integrity. Employing a Metropolis-Hastings method, a mono-energy and mono-pitch RE beam is initialized from a DIII-D current profile. After this initialization, RE drift and magnetization parallel currents are deposited onto NIMROD's FE mesh through a weighted deposition strategy. The adopted approach deposits accumulated currents along both passing and trapped orbits, representing a guiding center orbit-averaging current. The deposition strategy is inspired from the methods in Ref. [1,2], which were employed to construct quasi-static distributions for PIC simulations to prevent prompt relaxation. This strategy reduces the total number of REs required and ensures the generation of computationally manageable RE distributions. Additional algorithmic improvements include a new physical to logical search algorithm based on barycentric coordinates, which ultimately accelerates RE kinetic evolution.

 

[1] Bierwage et al, Comput. Phys. Comm. 183, 1107 (2012)

[2] Bierwage et al, Nucl. Fusion 53, 073007 (2013)