Geodesic Acoustic Mode in Toroidally Rotating Anisotropic Tokamaks

TL;DR

This paper derives an analytical dispersion relation for the geodesic acoustic mode (GAM) in toroidally rotating anisotropic tokamaks, revealing how anisotropy, temperature ratios, and rotation influence GAM frequency and damping.

Contribution

It provides the first analytical dispersion relation for GAM in rotating anisotropic tokamaks, highlighting the effects of anisotropy and temperature ratios on GAM behavior.

Findings

Increasing electron temperature raises GAM frequency when anisotropy is below a threshold.

Anisotropy generally increases GAM frequency.

Higher temperature ratio or anisotropy reduces Landau damping rate.

Abstract

Effects of anisotropy on the geodesic acoustic mode (GAM) is analyzed by using gyro-kinetic equations applicable to low-frequency microinstabilities in a toroidally rotating tokamak plasma. Dispersion relation in the presence of arbitrary Mach number $M$, anisotropy strength $\sigma$, and the temperature ration $\tau$ is analytically derived. It is shown that when $\sigma$ is less than $ 3 + 2 \tau$, the increased electron temperature with fixed ion parallel temperature increases the normalized GAM frequency. When $\sigma$ is larger than $ 3 + 2 \tau$, the increasing of electron temperature decreases the GAM frequency. The anisotropy $\sigma$ always tends to enlarge the GAM frequency. The Landau damping rate is dramatically decreased by the increasing $\tau$ or $\sigma$.