Divertor heat fluxes and profiles during mitigated and unmitigated Edge Localised Modes (ELMs) on the Mega Amp Spherical Tokamak (MAST)

TL;DR

This study investigates how resonant magnetic perturbations (RMPs) influence ELM behavior and divertor heat flux profiles on MAST, demonstrating that RMPs increase ELM frequency and reduce peak heat flux through strike point splitting.

Contribution

It provides experimental evidence of RMP effects on ELM mitigation and divertor heat flux profiles, including strike point splitting consistent with ERGOS modeling.

Findings

RMPs increase ELM frequency on MAST.

RMPs reduce ELM energy and peak heat flux.

Divertor heat flux profiles show strike point splitting.

Abstract

Edge localised modes (ELMs) are a concern for future devices as they can limit the operational lifetime of the divertor. The mitigation of ELMs can be performed by the application of resonant magnetic perturbations (RMPs) which act to degrade the pressure gradient in the edge of the plasma. Investigations of the effect of RMPs on MAST have been performed in a range of plasmas using perturbations with toroidal mode numbers of n=3, 4 and 6. It has been seen that the RMPs increase the ELM frequency, which gives rise to a corresponding decrease in the ELM energy. The reduced ELM energy decreases the peak heat flux to the divertor, with a three fold reduction in the ELM energy, generating a 1.5 fold reduction in the peak heat flux. Measurements of the divertor heat flux profile show evidence of strike point splitting consistent with modelling using the vacuum code ERGOS.