[Table of Contents]

Plasma and Fusion Research

Volume 8, 1403010 (2013)

Regular Articles

On a Nonlinear Dispersion Effect of Geodesic Acoustic Modes
Makoto SASAKI1,2), Kimitaka ITOH2,3), Naohiro KASUYA1,2), Klaus HALLATSCHEK2,4) and Sanae-I. ITOH1,2)
1)
Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580, Japan
2)
Itoh Research Center for Plasma Turbulence, Kyushu University, Kasuga 816-8580, Japan
3)
National Institute for Fusion Science, Gifu 509-5292, Japan
4)
Centre for Interdisciplinary Plasma Science, Max-Planck Institut für Plasmaphysik, EURATOM-IPP Association, D-85748 Garching, Germany
(Received 27 October 2012 / Accepted 27 December 2012 / Published 25 February 2013)

Abstract

The nonlinear dispersion relation of the geodesic acoustic modes (GAMs) is investigated for tokamaks with a high safety factor and low magnetic shear. We focus on the Reynolds stress as a nonlinearity, which is truncated at the third order of the GAM amplitude. The real frequency of the GAM is modified according to the phase of the nonlinear force acting on the GAM, which depends on the turbulence decorrelation rate. The nonlinear frequency shift is much larger than that from the finite gyro-radius effects in the linear theory, when the poloidal turbulent E × B velocities are comparable to the diamagnetic drift velocity. Under such circumstances, the group velocity is strongly enhanced and becomes comparable with the radial phase velocity. In addition, the magnitude of the nonlinear effects is also evaluated using experimental parameters.

Keywords

geodesic acoustic mode, zonal flow, drift wave, turbulence, dispersion relation, wave propagation

DOI: 10.1585/pfr.8.1403010

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This paper may be cited as follows:

Makoto SASAKI, Kimitaka ITOH, Naohiro KASUYA, Klaus HALLATSCHEK and Sanae-I. ITOH, Plasma Fusion Res. 8, 1403010 (2013).