49 / 2021-05-06 21:49:14

Feature of the Mitigation and suppression of ELM in the application of RMP on the HL-2A tokamak

RMP

Suppression and mitigation of type-I edge localized modes (ELMs) was achieved with a set of small-size resonant magnetic perturbation(RMP) coils in the n=1 configuration on the HL-2A tokamak. Enhanced broadband turbulence during ELM suppression is detected, suggesting that enhanced transport by RMP is responsible for ELM suppression. Furthermore, damping of poloidal plasma flow was measured, offering a mechanism by which turbulence is rapidly affected by the RMP. These experimental observations provide a coherent picture of increased radial transport by the RMP and the resulting relaxation of the plasma pressure pedestal profile against peeling-ballooning instabilities that are thought to drive type-I ELMs.

An edge coherent oscillation (ECO) with a bursting feature was observed in the steep-gradient pedestal region of the H-mode plasmas, where the type-I ELMs were mitigated. Utilizing a newly developed beam emission spectroscopy system (BES), it was found that the ECM with frequency of about 2 kHz is located at the edge pedestal region, and is excited by three-wave interaction of turbulence enhanced by the RMP field through the change of electron density gradient in the pedestal region because of pump-out effect. The mode drives a significant outflow of particles as directly measured by probes, thus providing a channel for a nearly continuous extra particle transport across the pedestal during the ELM mitigation by RMP.