Direct observation of current in type I ELM filaments on Asdex Upgrade

TL;DR

This paper provides direct magnetic measurements of type I ELM filaments in a tokamak, revealing they carry significant currents, which advances understanding of ELM dynamics and their impact on plasma confinement.

Contribution

It presents the first direct observation of current in type I ELM filaments, offering critical insights into their structure and role in ELM behavior.

Findings

ELM filaments carry substantial currents.

Magnetic field measurements elucidate filament structure.

Results inform models of ELM dynamics.

Abstract

Magnetically confined plasmas are often subject to relaxation oscillations accompanied by large transport events. This is particularly the case for the high confinement regime of tokamaks where these events are termed edge localized modes (ELMs). They result in the temporary breakdown of the high confinement and lead to high power loads on plasma facing components. Present theories of ELM generation rely on a combined effect of edge currents and the edge pressure gradient exceeding critical values which result in intermediate mode number ($n \cong 10-15$) structures (\emph{filaments}) localized in the perpendicular plane and extended along the field line. It is shown here by detailed localized measurements of the three components of the magnetic field perturbation carried by an individual type I ELM filament that these filaments carry a substantial current. The observations provide essential information for the understanding of ELM dynamics.