Chemical erosion of DIII-D divertor tile specimens

Abstract Chemical erosion measurements have been performed on graphite tile specimens taken from the upper and lower divertors of the DIII-D tokamak. Measurements for 50 eV/D+ incident on the lower divertor resulted in erosion yields which are the same as those for graphite. This implies that any deposited film on the tile surface was completely removed after very short beam exposures (∼1021 D+/m2). For the upper divertor tiles, the measured erosion yields for 50 and 200 eV/D+ were somewhat larger than those for graphite at 300 and 500 K; however, at 700 K the yields were lower than graphite yields and were more comparable to boron-doped graphite. Thermo-oxidation of both upper and lower divertor specimens also indicated the rapid removal of surface films, followed by the slower removal of implanted deuterium from the graphite substrate.