Abstract
Reduced erosion of a high-Z PFC divertor surface was observed in DIII-D with local injection of methane and deuterium gases. Molybdenum-coated silicon samples were exposed in the lower divertor of DIII-D using DiMES under plasma conditions previously shown to cause significant net erosion of Mo. Three exposures with (CH4)-C-13 and one exposure with D-2 gas injection about 12 cm upstream of the samples located within 1-2 cm of the attached strike point were performed. Reduction of Mo erosion was evidenced in-situ by the suppression of MoI line radiation at 386.4 nm once the gas injection started. Post-mortem ion beam analysis demonstrated that the net erosion of molybdenum near the center of the samples exposed with (CH4)-C-13 injection was below the measurement resolution of 0.5 nm, corresponding to a rate of <= 0.04 nm/s. Compared to the previously measured erosion rates, this constitutes a reduction by a factor of > 10. (C) 2014 Elsevier B.V. All rights reserved.