High Frequency Geodesic Acoustic Modes in Electron Temperature Gradient Mode Turbulence

TL;DR

This paper demonstrates a high frequency branch of geodesic acoustic modes driven by electron temperature gradient modes, revealing a new saturation mechanism that enhances ETG turbulence levels.

Contribution

It introduces the first demonstration of high frequency GAMs driven by ETG modes and derives their dispersion relation using a fluid model.

Findings

Identification of a high frequency GAM branch driven by ETG modes

Discovery of a new saturation mechanism for ETG turbulence

Enhanced turbulence saturation levels compared to previous estimates

Abstract

In this work the first demonstration of a high frequency branch of the geodesic acoustic mode (GAM) driven by electron temperature gradient (ETG) modes is presented. The work is based on a fluid description of the ETG mode retaining non-adiabatic ions and the dispersion relation for high frequency GAMs driven nonlinearly by ETG modes is derived. A new saturation mechanism for ETG turbulence through the interaction with high frequency GAMs is found, resulting in a significantly enhanced ETG turbulence saturation level compared to the mixing length estimate.