Abstract
Gross and net erosion rates of silicon from silicon carbide (SiC) coatings were measured in the divertor of DIII-D under well diagnosed reactor-relevant plasma conditions. Amorphous and crystalline SiC coatings on graphite with thickness of ~80 nm and ~250 μm, respectively, were exposed near an attached outer strike point of lower single null L-mode plasmas using the Divertor Material Evaluation System (DiMES). Plasma density and electron temperature near the center of the coatings were n e ~ 4 × 1019 m−3 and T e ~ 23 eV. Gross erosion of Si from all samples was measured spectroscopically using the Si II 636 nm line. It was found to be a factor of ~4 higher for the amorphous coatings compared to the crystalline one. The thin amorphous coatings allowed measurements of net Si erosion with Rutherford backscattering. Net average Si erosion rate of ~3 × 1016 cm−2 s−1 was measured on the amorphous coatings with toroidal extent of 1 mm, where, according to ERO code modeling, the local redeposition of Si was about 30%. Using this rate, spectroscopic measurements, measured D+ ion fluxes, and corrections from ERO-OEDGE modeling, effective SXB coefficient for the Si II 636 nm line of ~52 and Si sputtering yield of ~0.017 Si/D were calculated. Deuterium retention on SiC coatings was measured by 2.5 MeV 3He nuclear reaction analysis at 0.5–2.5 × 1017 atoms cm−2, consistent with retention due to implantation into a surface undergoing net erosion.
