Effect of resonant magnetic perturbations on low collisionality discharges in MAST and a comparison with ASDEX Upgrade

TL;DR

This study investigates how resonant magnetic perturbations (RMPs) influence ELM behavior in MAST and AUG tokamaks, showing that plasma response and careful fueling adjustments are key to effective mitigation with minimal plasma degradation.

Contribution

It demonstrates the importance of plasma response calculations and fueling strategies in optimizing RMP-induced ELM mitigation in tokamaks.

Findings

RMPs reduce ELM energy loss and divertor heat loads.

Plasma response, especially edge peeling-tearing modes, correlates with ELM frequency increase.

Adjusting fueling can mitigate ELMs without significant plasma performance loss.

Abstract

Sustained ELM mitigation has been achieved on MAST and AUG using RMPs with a range of toroidal mode numbers over a wide region of low to medium collisionality discharges. The ELM energy loss and peak heat loads at the divertor targets have been reduced. The ELM mitigation phase is typically associated with a drop in plasma density and overall stored energy. In one particular scenario on MAST, by carefully adjusting the fuelling it has been possible to counteract the drop in density and to produce plasmas with mitigated ELMs, reduced peak divertor heat flux and with minimal degradation in pedestal height and confined energy. While the applied resonant magnetic perturbation field can be a good indicator for the onset of ELM mitigation on MAST and AUG there are some cases where this is not the case and which clearly emphasise the need to take into account the plasma response to the applied perturbations. The plasma response calculations show that the increase in ELM frequency is correlated with the size of the edge peeling-tearing like response of the plasma and the distortions of the plasma boundary in the X-point region.