Solitary perturbations in the steep boundary of magnetized toroidal plasma

J E Lee,W Lee,G S Yun,M Kim,W H Ko,M H Kim,J Lee,M Choi,H K Park,Y S Park,J G Bak

doi:10.1038/srep45075

Abstract

Solitary perturbations (SPs) localized both poloidally and radially are detected within ~100 μs before the partial collapse of the high pressure gradient boundary region (called pedestal) of magnetized toroidal plasma in the KSTAR tokamak device. The SP develops with a low toroidal mode number (typically unity) in the pedestal ingrained with quasi-stable edge-localized mode (QSM) which commonly appears during the inter-collapse period. The SPs have smaller mode pitch and different (often opposite) rotation velocity compared to the QSMs. Similar solitary perturbations are also frequently observed before the onset of complete pedestal collapse, suggesting a strong connection between the SP generation and the pedestal collapse.

Highlights

High-confinement mode (H-mode) regime of toroidal magnetized plasma, which is the main operational regime for modern tokamak reactors, is characterized by improved energy and particle confinement connected to the formation of an edge transport barrier[1]
Another accurate indicator of the edge localized mode (ELM) crash is strong electromagnetic emission in the radio frequency (RF) range[14], which may be interpreted as ion cyclotron emission (ICE) attributed to the magnetoacoustic cyclotron instability (MCI) excited by the increase in the population of fusion-born particle at the edge of plasmas[15]
The partial ELM crash, which is the focus of this paper, is incomplete collapse of the edge pedestal during the recovery phase

Summary

Introduction

High-confinement mode (H-mode) regime of toroidal magnetized plasma, which is the main operational regime for modern tokamak reactors, is characterized by improved energy and particle confinement connected to the formation of an edge transport barrier ( called edge pedestal)[1]. On the Korea Superconducting Tokamak Advanced Research (KSTAR), quasi-stable edge-localized filamentary modes (QSMs) and their complex structural transitions without crash are routinely observed in H-mode discharges[7,8] using 2D electron cyclotron emission (ECE) imaging diagnostics[9]. These observations suggest QSMs are not directly linked to the crash trigger. On the KSTAR, solitary edge-localized perturbations (SPs) similar to SMPs are frequently observed within ~100 μs before the onset of partial pedestal collapse. Description of the SPs is followed based on measurements using 3D ECE imaging (ECEI) diagnostic[13] and toroidal Mirnov coil array

Methods

Results

Conclusion