Impact of n = 1 field on the non-axisymmetric magnetic perturbations associated with the edge localized mode crashes in the ASDEX Upgrade tokamak

Nengchao Wang,Li Li,Hendrik Meyer,The Eurofusion Mst1 Team ,Valentin Igochine,Louis Giannone,Peter Denner,Marc Maraschek,The Asdex Upgrade Team ,Yunfeng Liang,Yu Gao,Andrew Kirk,Matthias Bernert,Felician Mink,Wolfgang Suttrop,Michael Faitsch,Sina Fietz,Paolo Piovesan

doi:10.1088/1741-4326/ab0f82

Abstract

In the ASDEX Upgrade tokamak, the growth of non-axisymmetric magnetic perturbation (NAMP) associated with the ELM crash events has been observed, and both the poloidal and toroidal phases of NAMPs, measured by a set of Mirnov coils, were highly random. By applying an n = 1 magnetic perturbation (MP) field, the phases of NAMPs were locked to the phase of the total n = 1 resonant MP (RMP) field, which takes the plasma response to the MP field into account. This observation can be explained by the resonant electromagnetic J × B torque applied by the RMP field on a magnetic island formed due to the magnetic reconnection, which is predicted to occur during the ELM crashes by several numerical modelling results.

Highlights

Magnetic reconnection [8], which is followed by the formation of magnetic islands at the rational flux surfaces, plays a vital role for understanding the collapse events in magnetized plasmas, such as sawtooth crashes [9], minor disruptions [10] in tokamaks and solar flares [11] in the solar atmosphere
Plasmas, the magnetic island structure was directly described by the radial distribution of the nonaxisymmetric magnetic perturbations (NAMPs) [ 17 ] measured by magnetic probes around the rational surface
We report the observations from the ASDEX Upgrade tokamak experiments on the NAMPs with low toroidal mode number growing associated with the edge-localized mode (ELM) crash events, which are similar to those observed in TCV [28]

Summary

Introduction

Magnetic reconnection [8], which is followed by the formation of magnetic islands at the rational flux surfaces, plays a vital role for understanding the collapse events in magnetized plasmas, such as sawtooth crashes [9], minor disruptions [10] in tokamaks and solar flares [11] in the solar atmosphere. This observation can be explained by the resonant electromagnetic J×B torque, applied by the RMP field on a magnetic island due to the magnetic reconnection, which is predicted to occur during the ELM crashes by several numerical modelling results.

Results

Conclusion