SOLPS-ITER modeling of a new divertor for negative triangularity plasmas in DIII-D tokamak

SOLPS-ITER modeling with full drifts was used to determine the shape of a dedicated divertor for Negative Triangularity (NT) plasmas in DIII-D, favoring a closed divertor to reduce the detachment threshold density. The DIII-D NT campaign in 2023 successfully demonstrated its potential to be a solution to core-edge integration with improved confinement in an ELM-free regime. However, it requires very high densities to detach the divertor with confinement degradation due to the small divertor volume and short connection length. Thus, a dedicated new divertor is needed. A variety of divertor concepts was tested with different outer baffle shapes. It is found that the effects of divertor closure are modest in reducing the detachment threshold density with ion BΧ▽B drift into the divertor. However, a more closed divertor reduces parallel heat flux to the target by a factor of 2 -3. With ion BΧ▽B drift out of the divertor, the EΧB drifts push plasma from the inner divertor to the outer divertor, leading to significantly lower detachment onset density. The divertor closure plays a more profound role in this drift direction. The detachment onset density is reduced by ~30% in a closed divertor, accompanied by significantly reduced heat flux to the target, compared to a semi-open divertor.