Modeling first wall erosion and impurity migration: From fuel retention to W-core ingress

Abstract

Abstract

Erosion of the first wall and transport of impurities critically affect the operation of magnetic confinement fusion devices. Erosion limits component lifetimes, while high-Z impurity penetration into the core increases radiation and can degrade confinement. For low-Z materials, repeated transport and re-deposition lead to long-range migration and formation of co-deposited layers that can retain tritium. Driving the ITER material choices, the community’s focus has evolved from carbon migration and remote co-deposition to beryllium transport and co-deposition and now to tungsten erosion and ingress into the edge, pedestal, and core. This paper reviews the physics models applied to describe the underlying processes, trying to identify sources of uncertainty, in particular in the required input data. The modeling of first wall erosion and impurity migration is subdivided into three main sections: gross- vs. net-erosion, impurity transport in the scrape-off layer (SOL), and layer deposition. For predicting gross- vs. net-erosion, the main uncertainties lie in the sputter yield from surfaces with evolving surface roughness. The uncertainties in impurity plasma transport generally stem from the underlying plasma background solution, in particular the flow patterns, heat flux limiters, and the availability of electric fields for drift modeling. Finally, this paper outlines the required experimental data and model refinements needed to improve the predictive capabilities for future fusion devices.