Linear gyrokinetic investigation of the geodesic acoustic modes in realistic tokamak configurations

TL;DR

This paper uses gyrokinetic simulations to analyze geodesic acoustic modes in realistic tokamak configurations, providing new formulas for frequency and damping rate influenced by plasma parameters and applying findings to actual experimental data.

Contribution

It introduces interpolating formulas for GAM frequency and damping rate based on gyrokinetic simulations, accounting for realistic plasma conditions and parameters.

Findings

Derived formulas for GAM frequency and damping rate

Analyzed the impact of plasma parameters on GAM behavior

Applied results to real tokamak discharge data

Abstract

Geodesic acoustic modes (GAMs) are studied by means of the gyrokinetic global particle-in-cell code ORB5. Linear electromagnetic simulations in the low electron beta limit have been performed, in order to separate acoustic and Alfv\'enic time scales and obtain more accurate measurements. The dependence of the frequency and damping rate on several parameters such as the safety factor, the GAM radial wavenumber and the plasma elongation is studied. All simulations have been performed with kinetic electrons with realistic electron/ion mass ratio. Interpolating formulae for the GAM frequency and damping rate, based on the results of the gyrokinetic simulations, have been derived. Using these expressions, the influence of the temperature gradient on the damping rate is also investigated. Finally, the results are applied to the study of a real discharge of the ASDEX Upgrade tokamak.