The effect of neutrals in the new SAS divertor at DIII-D as modelled by SOLPS

Abstract

Abstract SOLPS5.1 modelling of first detachment experiments carried out in the new Small Angle Slot (SAS) divertor recently installed at DIII-D has indicated a significant reduction in Te at the strike point compared to a matched open divertor case for a given separatrix density. The SAS divertor combines a gas-tight slot geometry with a small target angle to bootstrap power and momentum dissipation of recycling neutrals with the goal of achieving simultaneous control of heat flux and erosion at relatively low plasma density required for non-inductive current drive in future steady-state tokamaks. The changes in the neutral ballistics influenced by the combination of closure and small angle target, result in a build-up of the neutral density in the slot, which promotes volumetric losses and facilitates detachment. Variations in the strike point location within the slot reveal a strong dependence of divertor cooling on the strike point location. This is due to the fact that by changing the strike point location, the region where the neutral leakage takes place is varied, thus affecting detachment. The results presented in this paper highlight the importance of controlling the neutral recycling flux to facilitate power dissipation.