Evidence of "Two Plasmon" decay of energetic particle induced geodesic acoustic mode

TL;DR

This paper investigates how energetic particles can induce a decay process in geodesic acoustic modes, leading to the generation of two GAMs, which enhances understanding of plasma wave interactions in fusion devices.

Contribution

It demonstrates the possibility of a two plasmon decay process of EGAM, expanding the understanding of mode interactions in low collisionality plasmas using nonlinear gyrokinetic theory.

Findings

EGAM frequency can exceed local GAM frequency in low collisionality plasmas.

EGAM can decay into two GAMs when its frequency approaches twice the GAM frequency.

The conditions for the two plasmon decay process are discussed.

Abstract

Secondary low frequency mode generation by energetic particle induced geodesic acoustic mode (EGAM) observed in LHD experiment is studied using nonlinear gyrokinetic theory. It is found that the EGAM frequency can be significantly higher than local geodesic acoustic mode (GAM) frequency in low collisionality plasmas, and it can decay into two GAMs as its frequency approaches twice GAM frequency, in a process analogous to the well-known two plasmon decay instability. The condition for this process to occur is also discussed.