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 O-2 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 (SigmaC(i)D(j)) erosion yields were initially found to be similar to0.01-0.02 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 similar to4 X 10(21)-3 X 10(22) D+/m(2). Above similar to3 X 10(22) D+/m(2) the yields level off. The initial erosion yields are found to be consistent with those for boron-doped graphite. O-2 gas exposure at 523 or 623 K initially removed similar to 25% of the trapped D; however, the remaining D could not be removed by baking in O-2 at temperatures up to 623 K. (C) 2001 Elsevier Science B.V. All rights reserved.