Evaluation of Small Angle Slot (SAS) divertor with toroidal tungsten-tile rings in DIII-D using OEDGE*

OEDGE has been used to model the W erosion, transport and deposition during the 2016 experiment that had two toroidal rings of W-tiles in the lower open divertor on DIII-D. The modeling approximately reproduces both the divertor-facing asymmetries and radial decay of the W deposition on an outer-midplane-SOL collector probe. A Small Angle Slot (SAS) with carbon tiles has been installed in the upper divertor of DIII-D. Initial experiments show that SAS divertor can achieve cold divertor plasmas at lower upstream plasma densities with low T_e across the target and over a large range of H-mode densities in some operation conditions, which is dependent on strike point locations. The performance of SAS divertor with tungsten rings is evaluated using the OEDGE code with coupled SOLPS plasma background solutions. Results for the effect of the location of the strike point and the location of tungsten sources are presented. Parameter scans of input power, upstream density and cross-field transport coefficient are also reported. This analysis will inform the next stage SAS upgrade with W rings in DIII-D.