Initial characterization of boron migration in the main chamber of WEST using the impurity collector probe*

The all tungsten (W) plasma facing components (PFCs) of WEST are an ideal testbed to develop operational requirements for the ITER W divertor and main chamber. To study the migration of boron (B) from wall conditioning in an all W environment, 4 W samples were installed in the reciprocating collector probe (RCP) to be exposed in the upstream scrape off layer (SOL) of WEST. The samples were exposed to 15 ICRH heated shots between 0.5 and 3.4 MW with medium to high densities up to 6e19 m^-3 during the C9 campaign in January 2024 and accumulated up to 1.3e22 ions/m² of plasma fluence on the most exposed sample. Based on the (B) content on the samples on each side of the probe we can evaluate the distribution of B in the far-SOL plasma as it’s been depleted from the W PFCs based on the magnetic field line connection lengths from the probe to the PFCs and the far-SOL temperature and density. The amount of B deposited on the samples is quantified using nuclear reaction analysis (NRA) and laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS), which are both capable of providing absolute measurements of the deposited density on the samples. X-ray photoelectron spectroscopy (XPS) is also performed on the samples to study the surface chemistry of the deposited B. The findings from this work will influence the analysis of the witness plates installed on the WEST main chamber walls during the full C9 campaign as well as future experiments comparing the sourcing and migration of B from glow discharge boronization and the impurity powder dropper as well as their impact on the growth of B deposition layers on the main wall of WEST.