Modeling of combined effects of divertor closure and advanced magnetic configuration on detachment in DIII-D by SOLPS

One of the major challenges facing the design and operation of next-step high-power steady-state fusion devices is to develop a divertor solution for handling power exhaust, while ensuring acceptable divertor target plate erosion, which necessitates access to divertor detachment at relative low main plasma densities compatible with current drive and high plasma confinement. Detailed modeling with SOLPS is carried out to examine the effect of divertor closure on detachment with the normal single null divertor (SD) configuration, as well as one of the advanced divertor configurations, such as x-divertor (XD) respectively. The SOLPS modeling for a high confinement plasma in DIII-D finds that increasing divertor closure with SD reduces the upstream separatrix density at the onset of detachment from $1.18\times {10}^{19}{m}^{-3}$ to $0.88\times {10}^{19}{m}^{-3}$. Moreover, coupling the divertor closure with XD further promotes the onset of divertor detachment at a still lower upstream separatrix density, down to the value of $0.67\times {10}^{19}{m}^{-3}$, thus, showing that divertor closure and advanced magnetic configuration can work synergistically to facilitate divertor detachment. (paper)