Effects of the Second Harmonic and Plasma Shaping on the Geodesic Acoustic Mode

TL;DR

This paper investigates how second harmonic effects and plasma shaping influence the frequency and generation of the Geodesic Acoustic Mode (GAM) in plasma, using a fluid model to analyze linear and non-linear behaviors.

Contribution

It introduces the impact of second harmonic perturbations and plasma shaping on GAM frequency and non-linear generation, extending previous models.

Findings

Second harmonics affect GAM frequency via density gradient and wave number.

Coupling to higher harmonics generally increases the linear GAM frequency.

Plasma shaping influences the nonlinear generation of GAM.

Abstract

The effects of second harmonics of the density and temperature perturbations on the linear Geodesic Acoustic Mode (GAM) frequency and non-linear generation of the GAM are investigated, using a fluid model. We show that the second harmonics contribute to the frequency through the density gradient scale length and the wave number of the GAM. In addition, the linear frequency of the GAM is generally increased by coupling to the higher harmonic.