Effect of time-varying flow-shear on the nonlinear stability of the boundary of magnetized toroidal plasmas

Youngmin Oh,Michael Leconte,Gunsu S Yun,Minwoo Kim,Hyung Ju Hwang

doi:10.1063/1.5006554

Abstract

We propose a phenomenological yet general model in a form of extended complex Ginzburg-Landau equation to understand edge-localized modes (ELMs), a class of quasi-periodic fluid instabilities in the boundary of toroidal magnetized high-temperature plasmas. The model reproduces key dynamical features of the ELMs (except the final explosive relaxation stage) observed in the high-confinement state plasmas on the Korea Superconducting Tokamak Advanced Research: quasi-steady states characterized by field-aligned filamentary eigenmodes, transitions between different quasi-steady eigenmodes, and rapid transition to non-modal filamentary structure prior to the relaxation. It is found that the inclusion of time-varying perpendicular sheared flow is crucial for reproducing all of the observed dynamical features.

Highlights

Relaxation phenomena in magnetized plasmas are widespread in nature.[1,2] A notable example is the explosive flares on the surface of the Sun
Inspired by Ref. 13, we mathematically studied the model equation to understand the effect of perpendicular flow shear on the nonlinear behavior of the perturbed pressure during the edge-localized modes (ELMs) cycle.[14]
We propose that the salient features of the ELM dynamics observed in the Korea Superconducting Tokamak Advanced Research (KSTAR) H-mode plasmas can be explained based on time-varying perpendicular shear flow

Summary

INTRODUCTION

Relaxation phenomena in magnetized plasmas are widespread in nature.[1,2] A notable example is the explosive flares on the surface of the Sun. A transport barrier (called pedestal) spontaneously appears at the edge of plasma via strong E × B flow shear which reduces heat and particle transports This barrier is quite unstable and prone to a class of fluid instabilities called edge-localized modes (ELMs) driven by the large gradient of density, temperature, current density, and flow.[3,4,5,6,7,8] It is believed that these instabilities are responsible for the relaxation (or crash) of the transport barrier, i.e., rapid expulsion of heat and particles.

ANALYSIS OF SINGLE-MODE

The effect of time-varying A

ANALYSIS OF COUPLED MODES

Long-time behavior on the linear growth terms

Long-time behavior for time-varying A

CONCLUSION