Analysis of a tungsten sputtering experiment in DIII-D and code/data validation of high redeposition/reduced erosion

We analyze a DIII-D tokamak experiment where two tungsten spots on the removable DiMES divertor probe were exposed to 12s of attached plasma conditions, with moderate strike point temperature and density (∼20eV, ∼4.5×1019m−3), and 3% carbon impurity content. Both very small (1mm diameter) and small (1cm diameter) deposited samples were used for assessing gross and net tungsten sputtering erosion. The analysis uses a 3-D erosion/redeposition code package (REDEP/WBC), with input from a diagnostic-calibrated near-surface plasma code (OEDGE), and with focus on charge state resolved impinging carbon ion flux and energy. The tungsten surfaces are primarily sputtered by the carbon, in charge states +1 to +4. We predict high redeposition (∼75%) of sputtered tungsten on the 1cm spot—with consequent reduced net erosion—and this agrees well with post-exposure DiMES probe RBS analysis data. This study and recent related work is encouraging for erosion lifetime and non-contamination performance of tokamak reactor high-Z plasma facing components.