TITLE

Variational derivation of the dispersion relation of kinetic coherent modes in the acoustic frequency range in tokamaks

AUTHOR(S)
Nguyen, C.; Garbet, X.; Smolyakov, A. I.
PUB. DATE
November 2008
SOURCE
Physics of Plasmas;11/1/2008, Vol. 15 Issue 11, p112502
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
In the present paper, we compare two modes with frequencies belonging to the acoustic frequency range: the geodesic acoustic mode (GAM) and the Beta Alfvén eigenmode (BAE). For this, a variational gyrokinetic energy principle coupled to a Fourier sidebands expansion is developed. High order finite Larmor radius and finite orbit width effects are kept. Their impact on the mode structures and on the Alfvén spectrum is calculated and discussed. We show that in a local analysis, the degeneracy of the electrostatic GAM and the BAE dispersion relations is verified to a high order and based in particular on a local poloidal symmetry of the two modes. When a more global point of view is taken, and the full radial structures of the modes are computed, differences appear. The BAE structure is shown to have an enforced localization, and to possibly connect to a large magnetohydrodynamic structure. On the contrary, the GAM is seen to have a wavelike, nonlocalized structure, as long as standard slowly varying monotonic profiles are considered.
ACCESSION #
35541240

 

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