Non-uniform carbon redeposition on graphite

Gradual erosion of a thin a-B:D layer on a graphite block is observed in TE XTOR-94 during 28 exposures while carbon out of the SOL has been deposited onto the surface simultaneously. The co-existence of B erosion (-0.5 nm/s) and C deposition (+0.8 nm/s) in the same area is due to non-uniform carbon redeposition of typically 10-30 mu m in size. The D content is more than do ubled in the co-deposit despite the considerable erosion of boron, Erosion by only neutrals could be discriminated from the erosion by D+ ions. The fi lm lost the transparency due to temperature excursions up to 2000 K during NBI, Observations were made during the exposures (colorimetry, spectroscopy ) and postmortem. (C) 1999 Elsevier Science B.V. All rights reserved.