Divertor detachment in MAST-U’s Super-X Double Null plasmas: SOLPS-ITER modeling and experiment

SOLPS-ITER simulations of MAST-U’s tightly baffled Super-X double-null divertor have highlighted the respective roles of divertor magnetic geometry and divertor baffle closure on divertor detachment as a function of upstream main-chamber plasma density. Simulations reproduce the experimental detachment front location, as determined by the peak in D₂ Fulcher band emission, when proper power accounting and radial transport based on upstream profiles are followed. The role of divertor baffling on leakage of recycling neutrals is examined by changing the fueling location in the simulations from the divertor chamber to the main chamber. Divertor chamber fueling coupled with tight baffling largely eliminates particle transport between the divertor and main chamber and represents the base case performance of the Super-X divertor. Main chamber fueling, either in the core or outboard midplane, resulted in higher upstream separatrix density for the same detachment conditions as the divertor fueled case. SOLPS-ITER reveals that increased convective transport into the outboard divertor was the primary cause of the higher upstream density. The experimental results and modeling highlight the benefits of both magnetic geometry and divertor baffling for achieving attractive dissipative divertor performance.

Work supported by US DOE under DE-SC0018991 and DE-FC02-04ER54698