Pedestal dynamics and turbulence in H-mode density ramp-up experiment on EAST

Abstract Recent results of density ramp-up (< n e >/ n GW = 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 ( p e ped ) decreases while the ELM frequency ( f ELM ) increases. Especially when < n e >/ n GW arrives at ∼ 0.68, a sudden decrease of p e ped and an increase of f ELM 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 p e ped during the inter-ELM phase is analyzed for different densities. The analysis suggests that the pedestal behavior for < n e >/ n GW < 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. Plasmas 24 062108) could be used to explain the present result. But the sudden decrease of p e ped and increase of f ELM at < n e >/ n GW > 0.68 cannot be attributed to the resistivity effect. It is found that for the plasma with < n e >/ n GW > 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 p e ped and increase of f ELM .