Some important issues for radiating mantle and divertor operation in AT plasmas*

We report on recent experiments that directly relate to the feasibility of applying radiating mantle or radiating divertor approaches to high performance single-null (SN) and double-null (DN) plasmas: H98 ≈ 1.3–1.7, betaN ≈ 3-4, and P_IN ≤ 15 MW. We explore the interplay of magnetic balance and divertor closure on controlling argon seed and deuterium inventory. Our results indicate that inner divertor pumping was far more important in controlling argon and deuterium inventories in SNs than it was for DNs. Detachment from the upper closed divertor led to strong reductions in divertor heat flux but also resulted in a rapid buildup in both carbon (intrinsic) and argon (injected) in the main plasma. Regardless of whether neon (low-Z) or argon (medium-Z) seeds were used, MHD activity evolved in essentially the same sequence, i.e., 4/2, 5/2, 3/1, and each mode added to the cumulative toll on t_E. Lowering the seed injection rates did not suppress these modes but only delayed their onset.