Access and sustainment of naturally ELM-free and small-ELM regimes

Edge localized modes (ELMs) have a detrimental effect on the plasma facing components and pose one of the most serious obstacles for steady-state operation in a future fusion device. For future fusion machines, the control or even full suppression of ELMs is mandatory. In the past years, extensive effort has been directed to the development of operational regimes that maintain the high confinement and good performance of the H-mode, while at the same time ELMs are suppressed or mitigated. Several natural ELM-free and small-ELM regimes, such as the quiescent H-mode, the improved energy confinement mode, the type-II and the grassy ELM-regime, have been obtained in various tokamaks. The state-of-the-art and recent advances of these ELM-free and small-ELM scenarios are reviewed, and the access and sustainment as well as their applicability to ITER are discussed. (special topic)