Recent results of density ramp-up (<ne>/nGW = 0.5–0.75) experiment in type-I ELMy H-mode on experimental advanced superconducting tokamak are presented, with a focus on pedestal dynamics and turbulence behavior. With the density increase, a general trend is that the pedestal electron pressure (peped) decreases while the ELM frequency (fELM) increases. Especially when <ne>/nGW arrives at ∼ 0.68, a sudden decrease of peped and an increase of fELM are observed. A quasi-coherent mode (QCM) with a frequency of 200–300 kHz is observed in the pedestal region and appears in both density and magnetic fluctuations. The time evolution of peped during the inter-ELM phase is analyzed for different densities. The analysis suggests that the pedestal behavior for <ne>/nGW < 0.68 is mainly attributed to pedestal stability but not due to pedestal transport. It is shown that the resistivity effect on the peeling-ballooning (PB) mode (Zhang et al 2017 Phys. Plasmas24 062108) could be used to explain the present result. But the sudden decrease of peped and increase of fELM at <ne>/nGW > 0.68 cannot be attributed to the resistivity effect. It is found that for the plasma with <ne>/nGW > 0.68, the QCM disappears just before ELM and the density pedestal becomes steeper. This implies that the QCM can drive outward particle transport. The steeper density pedestal leads to a narrower pedestal width. A narrower pedestal width will lead to a lower pedestal pressure since PB mode limits the pressure gradient and could explain the observed sudden decrease of peped and increase of fELM.
This paper investigates the behavior of the plasma pedestal and turbulence during a density ramp-up experiment in an H-mode tokamak. As the density increases, the pedestal electron pressure decreases and the ELM frequency increases, especially at a critical density ratio. The analysis suggests this is due to changes in pedestal stability and the appearance of a quasi-coherent mode that can drive particle transport.