Study on pedestal fluctuations in H-modes without large ELMs during the transition to a detached tungsten divertor in EAST

Abstract Simultaneous control of the damaging erosion induced by the transient and steady-state heat/particle fluxes on the divertor target material is one of the critical issues for next-step magnetic fusion devices. H-mode operation without large edge-localized modes has been achieved in EAST with an ITER-like tungsten divertor, while being compatible with the partial and pronounced detachment in divertor, via either ramping-up of bulk density or injection of low/high-Z impurities. The pedestal characteristics during the transition from the attached to the detached divertor and the reversed transition (detached to attached) under different detachment methods are studied in detail, where the evolution of multi fluctuating structures commonly residing in the H-mode pedestal of EAST (edge coherent mode (ECM), magnetic coherent mode (MCM) and high frequency mode (HFM)) is highlighted. In addition, the possible mechanisms that affect the behavior of these modes, such as the pedestal pressure gradient and the collisionality, have also been discussed. The radial structures of ECM, MCM and HFM are detected, for the first time, in one discharge. Relevant research may provide contribution to obtaining an integrated small/no ELM and radiative divertor scenario in the next step.