The effect of resonant magnetic perturbations on the divertor heat and particle fluxes in MAST

TL;DR

This study investigates how resonant magnetic perturbations influence divertor heat and particle fluxes in MAST, showing that RMPs can cause strike point splitting and potentially control ELMs, with effects varying during ELMs.

Contribution

The paper provides experimental evidence of strike point splitting due to RMPs on MAST and compares measurements with modelling, highlighting the dynamic nature of splitting during ELMs.

Findings

Clear strike point splitting observed in L-mode with RMPs.

Splitting varies during ELMs, peaking at maximum heat flux.

Some ELMs show no splitting, linked to phase differences.

Abstract

Edge localised modes (ELMs) are a concern for future devices, such as ITER, due to the large transient heat loads they generate on the divertor surfaces which could limit the operational time of the device. This paper discusses the application of resonant magnetic perturbations (RMPs) as a mechanism for ELM control on MAST. Experiments have been performed using an n=3 toroidal mode number perturbation and measurements of the strike point splitting performed. The measurements have been made using both infrared and visible imaging to measure the heat and particle flux to the divertor. The measured profiles have shown clear splitting in L-mode which compares well with the predication of the splitting location from modelling including the effect of screening. The splitting of the strike point has also been studied as a function of time during the ELM. The splitting varies during the ELM, being the strongest at the time of the peak heat flux and becoming more filamentary at the end of the ELM (200 microseconds after the peak midplane D(alpha) emission). Variation in the splitting profiles has also been seen, with some ELMs showing clear splitting and others no splitting. A possible explanation of this effect is proposed, and supported by modelling, which concerns the relative phase between the RMP field and the ELM filament location.