Operational limits of ASDEX upgrade H mode discharges in the new closed Divertor II configuration

Systematic investigations of gas fuelled, high density H mode discharges wi th the new closed Divertor II of ASDEX Upgrade are reported. The focus is o n operational limits (H-L transition, density limit) over a wide range of e xternally controllable plasma parameters. It is found that the H mode thres hold power dramatically exceeds the generally accepted prediction P-heat(th resh) proportional to <(<eta>)over bar>B-e(t) when high densities are appro ached. Highest densities (density limit) are achieved close to the H-L mode back-transition and are generally associated with complete divertor detach ment. The scaling of the density limit is assessed and discussed with a vie w to detachment based models and the Greenwald limit.