Interpretation of boron deposition patterns in the main chamber of WEST

In preparation for operation of ITER with full-W PFCs and a boronization system, samples were installed in the main chamber of WEST during the fall 2023 and spring 2024 campaigns to investigate the migration of material from thin films of boron (B) deposited by glow discharge boronization that are eroded away during operation. Samples were installed at 12 locations to evaluate toroidal and poloidal asymmetry of the redeposited layers and were exposed to ~6hrs of total plasma operation. Nuclear Reaction Analysis shows a poloidal asymmetry with thicker B layers at and above the high field side (HFS) midplane up to a factor of 6 greater than layers on samples close to the divertor and a toroidal asymmetry of roughly a factor of 2 in samples separated by roughly 150 degrees toroidally. Chemical bonding information between B, C, and O from XPS analysis is examined to determine if the impurity gettering properties of B are maintained after being eroded and redeposited by the plasma.

Modelling of a representative plasma from C9 with the SOLEDGE3X code is employed to infer expected erosion and deposition rates at the main chamber. The comparison between the modeling performed and post mortem highlights the impact of charge exchange fluxes on main chamber surface evolution during long pulse and steady states operations.

Work supported by the Department of Energy under Award Number(s) DE-SC0020414.