Stationary ELM-free H-mode in ASDEX Upgrade

A stationary H-mode without edge localized modes (ELMs) has been recently achieved in the ASDEX Upgrade tokamak by applying central electron cyclotron resonance heating above the L-H power threshold with adequate fueling. It is naturally obtained in favorable del B configuration and has several features which are desirable for future reactors, such as dominant electron heating, low input torque, possibility of access at low input power, good energy confinement (H-98y2 = 0.9-1.3), high density (f(GW) = 0.8-0.9), and no impurity accumulation despite the absence of ELMs. This regime is similar to the EDA H-mode and always features an edge electromagnetic quasi-coherent mode which seems to be responsible for enhanced transport losses, as its appearance and disappearance are correlated with changes in edge and divertor parameters.