Broadening of the power fall-off length in a high density, high confinement H-mode regime in ASDEX Upgrade

The search for scenarios in which tolerable power exhaust is combined with good confinement must involve high separatrix densities. We present here the first infrared thermography measurements at ASDEX Upgrade in a high density, high confinement H-mode regime in which no type-I ELMs are present. This regime was formerly called type-II ELM or small ELM regime to distinguish it from type-I ELMs. We report on a broadening of the power fall-off length in this regime of up to a factor of four compared to low density inter type-I ELM conditions. This broadening is correlated to an increased filament detection rate as well as an increase in the pressure close to the separatrix. The broadening of the fall-off length decreases the peak heat flux, while the filaments lead to a quasi-continuous transport into the scrape-off layer and onto the divertor. •A high density regime at high triangularity, close-to-double-null is investigated.•The power fall-off length is broadening in this quasi-continuous exhaust regime.•An increase of the filament frequency in the scrape-off layer is detected.•An increase of a turbulence control parameter just inside the separatrix is observed.