Analytic Theory of Edge Localized Mode Suppression by Static Resonant Magnetic Perturbations in H-mode Tokamak Discharges

TL;DR

This paper develops an analytic theory explaining how static resonant magnetic perturbations can suppress edge localized modes in H-mode tokamak plasmas, emphasizing mode penetration, nonlinear island physics, and plasma effects.

Contribution

It introduces a new analytic framework linking RMP-induced ELM suppression to mode penetration and nonlinear island physics, incorporating neoclassical effects and impurity roles.

Findings

ELM suppression occurs within narrow q_95 windows.

Window widths decrease with higher plasma density.

Similar window widths are predicted for ITER and DIII-D with specific rotation assumptions.

Abstract

An analytic theory of edge localized mode (ELM) suppression in an H-mode tokamak plasma via the application of a static, externally generated, resonant magnetic perturbation (RMP) is presented. This theory is based on the plausible hypothesis that mode penetration at the top of the pedestal is a necessary and sufficient condition for the RMP-induced suppression of ELMs. The theory also makes use of a number of key insights gained in a recent publication (Fitzpatrick R 2019). The first insight is that the response of the plasma to a particular helical component of the RMP, in the immediate vicinity of the associated resonant surface, is governed by nonlinear magnetic island physics, rather than by linear layer physics. The second insight is that neoclassical effects play a vital role in the physics of RMP-induced ELM suppression. The final insight is that plasma impurities play an important role in the physics of RMP-induced ELM suppression. The theory presented in this paper is employed to gain a better understanding ELM suppression in DIII-D and ITER H-mode discharges. It is found that ELM suppression is only possible when q_95 takes values that lie in certain narrow windows. Moreover, the widths of these windows decrease with increasing plasma density. Assuming a core plasma rotation of 20 krad/s, the window width for a model ITER H-mode discharge is found to be similar to, but slightly smaller than, the window width in a typical DIII-D H-mode discharge.