DIMES DIVERTOR EROSION EXPERIMENTS ON DIII-D

Thin metal films (similar to 100 nm thick) of Be, W, V and Mo, were de posited on a Si depth-marked graphite sample and exposed to the steady -state outer strike point on DIII-D in order to measure their respecti ve erosion rates. Gross erosion rates and redeposition lengths are fou nd to decrease with the atomic number of the metallic species, as expe cted. The maximum net erosion rate for carbon, which occurs near the s eparatrix, increased from 4 to 16 nm/s when the incident heat flux was increased from 0.7 to 2 MW/m(2). Comparisons of the measured carbon e rosion with REDEP code calculations show good agreement for both the a bsolute net erosion rate and its spatial variation. Visible spectrosco pic measurements of singly ionized Be (BeII 4674 Angstrom) have determ ined that the erosion process reaches steady-state during the exposure .