Resonant magnetic perturbations and divertor footprints in poloidally diverted tokamaks

TL;DR

This paper derives a comprehensive formula linking resonant magnetic perturbations to divertor footprint splitting and magnetic island width in poloidally diverted tokamaks, enhancing understanding of edge magnetic structures.

Contribution

It introduces a general formula connecting RMP-induced magnetic islands and divertor footprints, considering coil configurations typical for ELM control in tokamaks.

Findings

Derived a unified formula for island width and divertor splitting

Showed the relationship between coil configuration and magnetic structures

Explained the alignment of perturbation spectra with safety factor profiles

Abstract

General formula describing both the divertor strike point splitting and width of magnetic islands created by resonant magnetic perturbations (RMPs) in a poloidally diverted tokamak equilibrium is derived. Under the assumption that the RMP is produced by coils at the low-field side such as those used to control edge localized modes (ELMs) it is demonstrated that the width of islands on different magnetic surfaces at the edge and the amount of divertor splitting are related to each other. Explanation is provided of aligned maxima of the perturbation spectra with the safety factor profile - an effect empirically observed in models of many perturbation coil designs.