Effect of D2 mass injection rates on intra-ELM and inter-ELM W erosion and ELM peak heat flux in SAS-VW divertor in DIII-D

The effect of D₂ injection via gas puffing and pellets at the midplane on intra- and inter-edge localized mode (ELM) tungsten (W) erosion and peak heat flux in the Small Angle Slot (SAS) divertor has been studied in the DIII-D tokamak. The experiment distinguished the effect that D₂ injection has on divertor W erosion and ELM peak heat flux reduction. While a greater D₂ injection rate decreased the ELM peak heat flux, the impact on W erosion at the progressive angle outer strike point (OSP) position was not monotonic. The average intra-ELM W erosion per ELM was about 30% lower for D₂ injection shots compared to the no D₂ injection case. However, a larger D₂ injection rate led to more frequent, reduced amplitude ELMs and increased both the total intra- and inter-ELM W erosion rate. D_α (656.19 nm) and WI filterscopes (400.9 nm) detected ELM start times and inferred photon emission from eroded W atoms, respectively. Langmuir probes measured divertor n_e and T_e to convert the photon emission rate to W atoms/s using the S/XB method, surface eroding thermocouples (SETCs) measured ELM peak heat flux, and impurity collector probes (CPs) assessed the upstream W content. W erosion at the SAS vertex and collector probe W content is currently under investigation and will also be discussed.