Simulations of fast ion wall loads in ASDEX Upgrade in the presence of magnetic perturbations due to ELM mitigation coils

TL;DR

This study uses simulations to analyze how magnetic perturbations from ELM mitigation coils in ASDEX Upgrade affect fast ion wall loads, revealing that high total magnetic field strength can mitigate increased losses caused by the coils.

Contribution

It provides the first detailed simulation-based analysis of the impact of in-vessel ELM mitigation coils on fast ion confinement and wall loads in ASDEX Upgrade.

Findings

Magnetic perturbations significantly affect fast ion confinement at low magnetic field.

High total magnetic field reduces the impact of coil-induced perturbations on fast ion losses.

Simulated FILD signals reasonably match experimental observations.

Abstract

The effect of ASDEX Upgrade (AUG) ELM mitigation coils on fast ion wall loads was studied with the fast particle following Monte Carlo code ASCOT. Neutral beam injected (NBI) particles were simulated in two AUG discharges both in the presence and in the absence of the magnetic field perturbation induced by the eight newly installed in-vessel coils. In one of the discharges (#26476) beams were applied individually, making it a useful basis for investigating the effect of the coils on different beams. However, no ELM mitigation was observed in #26476, probably due to the low plasma density. Therefore, another discharge (#26895) demonstrating clear ELM mitigation was also studied. The magnetic perturbation due to the in-vessel coils has a significant effect on the fast particle confinement, but only when total magnetic field, $B_{tot}$, is low. When $B_{tot}$ was high, the perturbation did not increase the losses, but merely resulted in redistribution of the wall power loads. Hence, it seems to be possible to achieve ELM mitigation using in-vessel coils, while still avoiding increased fast ion losses, by simply using a strong $B_{tot}$. Preliminary comparisons between simulated and experimental Fast Ion Lost Detector (FILD) signals show a reasonable correspondence.