Model for screening of resonant magnetic perturbations by plasma in a realistic tokamak geometry and its impact on divertor strike points

TL;DR

This paper models how plasma screening currents in a realistic tokamak geometry influence magnetic perturbations and strike-point splitting, providing insights into observable effects and screening mechanisms.

Contribution

It introduces a model with multiple screening current sheets to simulate plasma screening of magnetic perturbations in tokamaks, highlighting their impact on strike-point splitting.

Findings

Screening current sheets reduce strike-point splitting.

Multiple screening sheets reinforce each other's effects.

Screening effects should be observable experimentally.

Abstract

This work addresses the question of the relation between strike-point splitting and magnetic stochasticity at the edge of a poloidally diverted tokamak in the presence of externally imposed magnetic perturbations. More specifically, ad-hoc helical current sheets are introduced in order to mimic a hypothetical screening of the external resonant magnetic perturbations by the plasma. These current sheets, which suppress magnetic islands, are found to reduce the amount of splitting expected at the target, which suggests that screening effects should be observable experimentally. Multiple screening current sheets reinforce each other, i.e. less current relative to the case of only one current sheet is required to screen the perturbation.