Understanding the effect resonant magnetic perturbations have on ELMs

TL;DR

This paper reviews how resonant magnetic perturbations (RMPs) influence edge localized modes (ELMs) in tokamaks, highlighting their potential to mitigate or suppress ELMs and discussing the importance of 3D plasma effects for future predictive modeling.

Contribution

It provides a comprehensive overview of RMP effects on ELM behavior across different collisionality regimes and emphasizes the need to incorporate 3D effects into predictive plasma codes.

Findings

RMPs can suppress or mitigate ELMs depending on operational parameters.

At ITER-like collisionality, RMPs prevent ELMs by enhancing transport and keeping pressure gradients below critical.

ELM mitigation is more readily achievable than suppression across operational ranges.

Abstract

All current estimations of the energy released by type I ELMs indicate that, in order to ensure an adequate lifetime of the divertor targets on ITER, a mechanism is required to decrease the amount of energy released by an ELM, or to eliminate ELMs altogether. One such amelioration mechanism relies on perturbing the magnetic field in the edge plasma region, either leading to more frequent, smaller ELMs (ELM mitigation) or ELM suppression. This technique of Resonant Magnetic Perturbations (RMPs) has been employed to suppress type I ELMs at high collisionality/density on DIII-D, ASDEX Upgrade, KSTAR and JET and at low collisionality on DIII-D. At ITER-like collisionality the RMPs enhance the transport of particles or energy and keep the edge pressure gradient below the 2D linear ideal MHD critical value that would trigger an ELM, whereas at high collisionality/density the type I ELMs are replaced by small type II ELMs. Although ELM suppression only occurs within limitied operational ranges, ELM mitigation is much more easily achieved. The exact parameters that determine the onset of ELM suppression are unknown but in all cases the magnetic perturbations produce 3D distortions to the plasma and enhanced particle transport. The incorporation of these 3D effects in codes will be essential in order to make quantitative predictions for future devices.