Abstract
The relationship between the tungsten gross erosion and the edge-localized mode (ELM) characteristics is investigated for high performance discharges during the dedicated metal rings campaign in DIII-D, using the 1D 'free-streaming' ELM model, coupled to a simple analytical TRIM.SP sputtering model, while the OEDGE code is employed to calculate the inter-ELM impurity distribution and tungsten gross erosion. A carbon–tungsten mixed target material is used for both inter- and intra-ELM simulations. The OEDGE results reveal that the inter-ELM tungsten gross erosion rate is not sensitive to the carbon fraction on the tungsten surface layer; a wider range of carbon fractions from 0.3 to 0.6 gives similar tungsten gross erosion profiles and matches the diagnostic data, which is consistent with the simple analytical model. However, the intra-ELM simulation indicates that the value of the surface carbon fraction can be as low as 0.3 to reproduce the measured tungsten gross erosion during ELMs, based on the effective ionizations/photon (S/XB) value of WI emissions. For both inter- and intra-ELM cases, carbon is predicted to dominate the tungsten erosion. However, in contrast to the inter-ELM tungsten erosion, which is dominated by locally redeposited C2+, the energetic C6+ originating from the pedestal can contribute substantial tungsten erosion in the near-separatrix region during ELMs, and the width of this C6+ dominated region exhibits a negative correlation with the heat flux density carried by ELMs.
