Deuterium irradiation studies of lithium and boron coatings on graphite samples from NSTX-U*

During the 2015-2016 NSTX-U experimental campaign, a plasma facing component (PFC) diagnostic, the Material Analysis and Particle Probe (MAPP), was installed. MAPP has the capability studying materials without exposing them to atmospheric conditions. The first MAPP results have shown what occurs to boron layers on graphite and molybdenum on a day-to-day basis.

The next NSTX-U campaign will continue to feature a full graphite wall, and both boron and lithium will be used as PFC conditioning techniques. While the surface dynamics of Li-C-O complexes are fairly well understood, the dynamics of Li-B-C-O surfaces are not. Experiments were conducted at the IGNIS facility at UIUC. Cored graphite tiles from the last campaign were used. These tiles contain on average 15-30% B, according to XPS analysis. The samples were dosed with Li and then irradiated with D. XPS was performed on the samples for various steps of deposition and irradiation. In addition to providing insight into the surface processes of deuterium retention, offline experiments of these systems will provide a baseline for MAPP measurements during the next NSTX-U campaign.