SOLPS analysis of changes in the main SOL of DIII-D associated with divertor detachment vs attachment and closure vs openness

Abstract

Edge plasma code SOLPS modeling has been used to assess the effects of divertor detachment vs attachment and closure vs openness on the main scrape-off layer (SOL) plasma in DIII-D. The differences between the inner divertor and outer divertor, and the effects of divertor closure on the outer-midplane SOL plasma, have been analysed. It is found that the divertor shape and plasma state have significant influence on the SOL and pedestal plasma. (i) The inner divertor has a more significant effect on the high-field side (HFS) SOL than the outer divertor does on the low-field side (LFS) SOL, and for increasing main plasma density the ionization region in the HFS moves gradually from the divertor target into the HFS SOL, forming a high-density front in the high density discharge case. Also, particle flux reversal occurs near the separatrix. (ii) It is confirmed that divertor closure has a significant effect on the main SOL and pedestal plasma. Comparing an open and a closed divertor, it is found that for the closed divertor the ne radial profile at the OMP is higher outside the separatrix and lower inside it, due to the combined effects of the D+ and C impurity ion density. Moreover, the open divertor has higher core fueling than the closed divertor, and the closed divertor has better fuel and impurity neutral screening than the open divertor. (iii) The in/out asymmetry is also influenced by the divertor closure, increase of the closure of the outer divertor can substantially reduce the asymmetry. The closed divertor also has much higher HFS SOL density than that of the LFS SOL. These results highlight the strong dependence of neutral/impurity screening and main SOL properties on divertor geometry and plasma regimes, which needs to be taken into account in advanced divertor design for fusion reactors.