Modeling of runaway electrons dissipation with high-Z impurities in DIII-D post-disruption plateau regimes*

We present a simulation study of the dissipation of runaway electrons (RE) due to high-Z impurities in DIII-D post-disruption plasmas at plateau regimes. This study utilizes the Kinetic Orbit Runaway electron Code (KORC) to model RE dynamics and mitigation processes including regular collisions, and large-angle collisions resulting in secondary avalanche source of RE. Stochastic differential equations are used to evolve the momentum and pitch angle of REs, accurately representing the transport coefficients including the physics of partially ionized and neutral impurities. A 1D neutral diffusion model is coupled to KORC to improve the prediction of the observed RE current dissipation using avalanche theory. Additionally, computationally efficient, and robust algorithms for RE initialization and avalanche source are implemented. The study focuses on the evolution of spatiotemporal electron and impurity density profiles resulting from impurity injection and their interaction with RE drift orbits in dynamic fields. Understanding and accurately modeling plasma profiles in these simulations is crucial for enhancing the understanding and improvement of RE dissipation processes.