KORC Modeling of Wall Heating by Avalanche Runaway Electrons During a Final Loss Event in DIII-D

This work extends the recent modeling of runaway electron (RE) mitigation in Ref. [1] by including an avalanche RE source in the Kinetic Orbit Runaway electrons Code (KORC). We find that REs produced by the avalanche source are the primary contributor to transient surface heating of plasma-facing components (PFCs). The magnitude of the calculated heating is comparable to that for DIII-D graphite tile ablation and features of the simulated PFC surface heating qualitatively agree with infrared imaging of the first wall tiles in DIII-D only when the avalanche source is included. The KORC simulations presented in this work evolve a distribution of tracer RE guiding center orbits using a time series of experimental reconstructions of the electromagnetic fields. Fokker-Planck and large-angle collisions with the effects of partially-ionized impurities are employed assuming uniform and constant plasma and impurity profiles with magnitudes inferred from experimental observations. To calculate the PFC surface heating due to RE deposition, we have extended the 1D model from Ref. [2] to include the energy dependence of the deposition length scale. [1] Beidler et al., Phys. Plasmas 27, 112507 (2020) [2] Martín-Solís et al., Nucl. Fusion 54, 083027 (2014)