# On Zero Frequency Zonal Flow and Second Harmonic Generation by Finite Amplitude Energetic Particle Induced Geodesic Acoustic Mode

## TL;DR

This paper investigates how finite amplitude energetic particle induced geodesic acoustic modes (EGAM) can generate zero frequency zonal flows and second harmonics through nonlinear interactions, highlighting the dominant role of energetic particles.

## Contribution

It reveals that energetic particles primarily drive the nonlinear generation of ZFZF and second harmonic in EGAM, advancing understanding of zonal mode stabilization.

## Key findings

- Both ZFZF and second harmonic can be driven by finite amplitude EGAM.
- Energetic particles dominate the nonlinear coupling effects.
- Finite amplitude coupling via EPs enables second harmonic generation.

## Abstract

Nonlinear self-interaction of finite amplitude energetic particle induced geodesic acoustic mode (EGAM) is investigated using nonlinear gyrokinetic theory. It is found that both zero frequency zonal flow(ZFZF) and second harmonic can be driven by finite amplitude EGAM, with energetic particles (EPs) playing a dominant role in the nonlinear couplings through finite orbit width effects. For ZFZF, the effects of EPs on EGAM nonlinear self-coupling dominate that of the thermal plasmas which are also present; while the second harmonic generation is only possible via finite amplitude coupling though EPs. Our findings may improve the understanding of stabilizing zonal modes, and consequently, drift wave turbulence.