Surface erosion in the plasma-edge of ISX-B

Surface erosion of thin Au films has been directly observed for samples exposed to H2 and D2 discharges at various locations and orientations in the plasma-edge of ISX-B. The erosion of Au as well as the accumulation of D, O and Fe on the samples was determined using ion scattering, channeling and nuclear reaction techniques. Erosion rates varied from ~0.1 nm/discharge at 2 cm behind the limiter to near zero as the wall was approached. Comparable erosion rates were observed for H2 and D2 plasmas. The results are consistent with a dominant role for O sputtering (in the absence of arcing) for erosion at the limiter radius in ISX-B with negligible erosion at the wall.