High-Z material erosion and its control in DIII-D carbon divertor. (August 2017) - Ding, R.
Highlights: Dedicated DIII-D experiments coupled with ERO modeling deepen our understanding of high-Z material erosion and re-deposition. The sheath properties and carbon impurities play a critical role in determining high-Z materials erosion. The high-Z material erosion has been successfully suppressed by local gas puffing. Abstract: As High-Z materials will likely be used as plasma-facing components (PFCs) in future fusion devices, the erosion of high-Z materials is a key issue for high-power, long pulse operation. High-Z material erosion and redeposition have been studied using tungsten and molybdenum coated samples exposed in well-diagnosed DIII-D divertor plasma discharges. By coupling dedicated experiments and modelling using the 3D Monte Carlo code ERO, the roles of sheath potential and background carbon impurities in determining high-Z material erosion are identified. Different methods suggested by modelling have been investigated to control high-Z material erosion in DIII-D experiments. The erosion of Mo and W is found to be strongly suppressed by local injection of methane and deuterium gases. The 13 C deposition resulting from local 13 CH4 injection also provides information on radial transport due toE × B drifts and cross field diffusion. Finally, D2 gas puffing is found to cause local plasma perturbation, suppressing W erosion because of the lower effective sputtering yield of W at lower plasma temperature and for higher carbon concentration in the mixed surface layer.