Modeling dynamic wall recycling effects on edge plasma transport.*

Plasma-wall interactions in tokamaks play an essential role in fusion plasma particle and energy balance via the plasma recycling process. Recycling is most intense in the divertor region and involves complex interactions between plasma and the wall material, which strongly depend on both plasma and wall conditions. Therefore, it is important to consider the plasma recycling process dynamically, in particular for transient phenomena, such as edge localized modes (ELMs), and edge plasma transport instabilities. We conduct dynamic 2D edge plasma-wall simulations using the plasma transport code UEDGE and the wall reaction-diffusion code FACE coupled within the Integrated Plasma Simulation (IPS) framework. The simulations demonstrate that the dynamic recycling affects the amplitude and phase relations between perturbations of plasma parameters at the plasma-wall interface, as compared to a conventional static wall model. The dynamic changes in recycling during ELMs and their feedback on ELM pulse evolution are analyzed. We also investigate the possibility of a recently proposed divertor plasma recycling instability mechanism related to ExB drifts [1].

[1] S.I. Krasheninnikov, Plasma Phys. Reports 47, 407 (2021).