Application of a Kinetic-Analytic Model for Edge Localized Modes to Fast Tungsten Sputtering Measurements in the DIII-D Divertor

The roles of deuterium and low-Z impurities in tungsten sourcing during ELMs in an ITER-like mixed materials environment have been quantified in the DIII-D divertor with high temporal and spatial resolution. These findings are consistent with the Fundamenski-Moulton 'free-streaming' (FMFS) model predictions of how the W source scales with ELM deposited energy density. The modified FMFS model utilizes plasma conditions at the pedestal top as input and accounts for enhanced target electron densities and ion fluxes due to neutral recycling during ELMs to calculate ion impact energies and flux densities on the divertor targets. This model shows that the energetic 'free-streaming' D⁺ and C⁶⁺ ions originating inside the confined plasma volume dominate W sourcing during ELMs, despite comprising a relatively small fraction of the total ELM ion flux, because the high impact energy of these ions causes substantial physical sputtering of tungsten. Quantitative agreement across a range of ELM frequencies and sizes is observed between spectroscopic measurements of intra-ELM gross erosion of tungsten and this model when coupled to SDTrim.SP sputtering calculations. Interpretive modeling for the spatial profile of tungsten erosion during and between ELMs was also developed via OEDGE. It includes full mixed-material effects, W self-sputtering and both carbon and main ion sputtering. In contrast to the JET-ILW environment, the inter-ELM phase dominates the time-averaged W divertor source due to the more efficient physical sputtering process of C on W, relative to Be on W, in the sub-keV ion impact energy regime. This work represents major progress towards a predictive model linking pedestal conditions to the ELM-induced high-Z divertor source, essential for ITER and beyond where W sputtering due to ELMs may dominate the tungsten divertor source and overall high-Z core impurity accumulation.