The dispersion modification of electrostatic geodesic acoustic mode by electron geodesic drift current

TL;DR

This paper investigates how electron geodesic drift current modifies the dispersion relation of electrostatic geodesic acoustic modes, revealing increased frequency and reduced damping rate due to electron flow effects.

Contribution

It introduces the flow of electron geodesic current into the drift kinetic theory to analyze its impact on GAM dispersion, a novel approach in this context.

Findings

FEGC increases GAM frequency

FEGC reduces GAM damping rate

FEGC alters GAM characteristics as functions of safety factor q

Abstract

The past studies treated the perturbed distribution of circulating electrons as adiabatic one when studying the dispersion relation of electrostatic geodesic acoustic mode(GAM). In this paper, the flow of electron geodesic current (FEGC) is added to modify this adiabatic distribution. Based on the drift kinetic theory, it is found that FEGC obviously increases the magnitude of the standard GAM's frequency and reduces its damping rate. The increase of frequency results from the contribution of FEGC to the radial flow. The reason for the reduction of damping rate is that when the effect of FEGC counts, the new resonant velocity becomes much larger than ions thermal velocity with equilibrium distribution obeying Maxwellian distribution, compared with unmodified Landau resonant velocity. Especially, FEGC changes the characters of the frequency and damping rate of low-frequency GAM as functions of safety factor $q$ .