Simulated trends in tungsten erosion and scrape-off layer transport for the new V-shaped, tungsten-coated Small Angle Slot divertor in DIII-D

Narrowing the slot of the DIII-D Small Angle Slot (SAS) divertor to a V-shaped vertex via changes to the inboard baffle is predicted to lower gross erosion of the outboard tungsten (W) coating by a factor of 50 due to increased neutral confinement when the ion grad-B drift is towards the X-point. SOLPS-ITER edge plasma and DIVIMP impurity tracking simulations show that moving the outer strike point (OSP) more than a few cm away from the slot vertex or operating below the detachment threshold will likely negate any benefit of the V-shape, yielding erosion rates that match or exceed that calculated from the original SAS shape. However, moving the OSP outward 4 cm from the slot vertex is also predicted to reduce the fraction of eroded W into the upstream scrape-off layer by a factor of 2. A new, sheath-based prompt redeposition model estimated an average W redeposition fraction in SAS-VW of 0.74 when the OSP is at the slot vertex, improving the accuracy of net erosion estimates in regions of high electron temperature. Predictive modeling of W sourcing and transport in SAS-VW provides useful guidance for future DIII-D experiments, as well as valuable insight into the feasibility of high-Z, closed divertors for reactor-relevant scenarios.