Speaker
Description
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 review traces that evolution and assesses predictive capability.
On the erosion side, energetic ions and charge-exchange neutrals cause physical (and in some systems chemical) sputtering. Quantitative prediction remains limited by evolving surface roughness and microstructure, complex carbon chemistry, and the distinction between gross and net erosion under local re-deposition.
Impurity transport is often treated in trace approximation using codes with varying fidelity, from gyrocenter-averaged solvers (e.g., DIVIMP) to gyro-orbit–resolved tools (e.g., ERO, IMPGYRO). Regardless of fidelity, predictive capability is constrained by the accuracy of the background scrape-off-layer (SOL) plasma solution. Numerous impurity seeding experiments (JET, AUG, W7‑X, TEXTOR, DIII‑D) have been used for validation, but the tight coupling of surface processes and plasma transport complicates isolating transport alone. Layer formation modifies source distributions and the impurity influx, necessitating self-consistent modeling of surface composition evolution. WallDYN addresses this by coupling plasma impurity fluxes with dynamic wall composition, capturing multi-step (re-)erosion and (re-)deposition and long-range migration.
ITER and future devices will primarily use tungsten first walls, mitigating low-Z co-deposition with fuel. However, boronization may be needed for startup conditioning, requiring validated predictions on boron transport and co-deposition for tritium management. For tungsten, core ingress of high-Z impurities is a central concern. AUG and JET experiments demonstrate heating scenarios that suppress core accumulation and show strong divertor compression of high-Z species. Impurity ingress reflects competition between parallel SOL transport from main-chamber sources toward the divertor sink and radial transport into the core. This shifts the emphasis from divertor to main-chamber SOL impurity transport studies. This also demands improved, validated main-chamber plasma models, especially for parallel flow patterns.
This presentation will review the attempts to validate the erosion/migration code packages, point out the main sources of uncertainty and outline the required experimental data and model refinements needed, to improve the predictive capabilities for future fusion devices.