Closure is a feature of divertors expected to have several advantages for core-edge integration in tokamaks, yet one that requires much more detailed and extensive study. In this work, the impacts of closure on a hydrogenic plasma are studied in isolation, through artificial fixed-fraction impurity SOLPS-ITER simulations. These simulations are of a connected double null Super-X divertor on the MAST-U tokamak, with extreme cases of a closed and open divertor. Simulations show the closed geometry has two orders of magnitude higher neutral compression, allowing better decoupling of core and edge fueling when pellets are used. The open divertor also shows an 85% higher density required for detachment access compared to the closed divertor. However, at high powers, this impact of closure on detachment is reduced to 20%, explained by the increased neutral and cross-field losses in the open geometry. Once detached, the open divertor radiative losses scale more strongly with increasing density, and the open divertor shows radiation along the entire plasma edge, which moves upstream and inward into the core as detachment evolves, in contrast to the localized front radiation of the closed divertor.
Cowley et al. (Sun,) studied this question.