Effect of temperature anisotropy on the dynamics of geodesic acoustic modes

TL;DR

This paper investigates how ion temperature anisotropy influences the behavior of geodesic acoustic modes (GAMs) using gyro-kinetic theory, revealing that anisotropy increases GAM frequency and growth rate, with effects modulated by electron-ion temperature ratios.

Contribution

The study derives a general dispersion relation for GAMs with arbitrary ion distributions and analyzes the impact of ion temperature anisotropy on GAM dynamics.

Findings

Ion temperature anisotropy increases GAM frequency.

Ion temperature anisotropy enhances GAM growth rate.

Electron to ion temperature ratio significantly affects GAM modifications.

Abstract

In this work, we revisit the linear gyro-kinetic theory of geodesic acoustic modes (GAMs) and derive a general dispersion relation for an arbitrary equilibrium distribution function of ions. A bi-Maxwellian distribution of ions is then used to study the effects of ion temperature anisotropy on GAM frequency and growth rate. We find that ion temperature anisotropy yields sensible modifications to both the GAM frequency and growth rate as both tend to increase with anisotropy and these results are strongly affected by the electron to ion temperature ratio.