Chemical erosion of boronized films from DIII-D tiles

Tile specimens from the DIII-D tokamak have been studied to determine their erosion characteristics when exposed to D+ ions and O2 gas. Here, we report results for tile surfaces from the outer midplane. Surface analyses (EDX, XPS, SIMS) indicate that the surface layer is composed primarily of boron, with an overlayer of a B/C mixture. Total hydrocarbon (ΣCiDj) erosion yields were initially found to be ∼0.01–0.02 C/D+, with limited variations due to D+ energy (50 or 200 eV) or specimen temperature (300–700 K). Erosion yields were seen to decrease with fluence by a factor of 1.5–2 over the range ∼4×1021–3×1022 D+/m2. Above ∼3×1022 D+/m2 the yields level off. The initial erosion yields are found to be consistent with those for boron-doped graphite. O2 gas exposure at 523 or 623 K initially removed ∼25% of the trapped D; however, the remaining D could not be removed by baking in O2 at temperatures up to 623 K.