Energy and particle balance during plasma detachment in alternative divertor configurations*

Comprehensive studies of energy and particle balances in the transition to plasma detachment in alternative divertor configurations are shown. Numerical simulations are performed with the 2D code suite SOLPS 4.3, using an up-down, disconnected double null grid with narrow, tightly baffled long poloidal leg divertors at the outer lower target and outer upper target. A density scan is performed using the "closed gas box" model, where the tunable parameter in the simulations is the total number of deuterium particles in the simulation space and all other parameters are held fixed, including a constant input power and trace neon impurity radiation, to assess the physics of the transition to detachment in the system as the density increases. Three main aspects of the physics of divertor detachment are addressed: the distribution of heat flux and other plasma parameters between the four divertors as each divertor transitions to detachment, the criteria for the local onset of divertor detachment in each of the divertors, and the role of neutrals and fluxes to the walls in the transition to the detached regime. These results are compared to the existing understanding of the physics of the transition to plasma detachment in standard divertors.