Measurement of zero-frequency fluctuations generated by coupling between Alfven modes in the JET tokamak

TL;DR

This paper reports the first experimental detection of a zero-frequency fluctuation in a tokamak, generated by Alfvén modes, which correlates with improved plasma confinement despite energetic particle transport.

Contribution

First experimental observation of a zero-frequency fluctuation coupled with Alfvén modes in a tokamak, confirming theoretical predictions and linking it to enhanced plasma confinement.

Findings

Zero-frequency fluctuation observed in JET tokamak

Fluctuation linked to Alfvén mode interactions

Improved core plasma confinement observed

Abstract

We report the first experimental detection of a zero-frequency fluctuation that is pumped by an Alfv\`en mode in a magnetically confined plasma. Core-localized bidirectional Alfv\`en modes of frequency inside the toroidicity-induced gap (and its harmonics) exhibit three-wave coupling interactions with a zero-frequency fluctuation. The observation of the zero-frequency fluctuation is consistent with theoretical and numerical predictions of zonal modes pumped by Alfv\'en modes, and is correlated with an increase in the deep core ion temperature, temperature gradient, and confinement factor $H_{89,P}$. Despite the energetic particle transport induced by the Alfv\`en eigenmodes, the generation of a zero-frequency fluctuation that can suppress the turbulence leads to an overall improvement of confinement.