Issue
EPL
Volume 83, Number 3, August 2008
Article Number 35001
Number of page(s) 6
Section Physics of Gases, Plasmas and Electric Discharges
DOI http://dx.doi.org/10.1209/0295-5075/83/35001
Published online 01 July 2008
EPL, 83 (2008) 35001
DOI: 10.1209/0295-5075/83/35001

Radial structures and nonlinear excitation of geodesic acoustic modes

F. Zonca1 and L. Chen2, 3

1  Associazione Euratom-ENEA sulla Fusione, C.R. Frascati - C.P. 65, 00044 Frascati, Italy, EU
2  Department of Physics and Astronomy, University of California - Irvine, CA 92697-4575, USA
3  Institute for Fusion Theory and Simulation, Zhejiang University - Hangzhou 310027, PRC

zonca@frascati.enea.it

received 26 May 2008; accepted in final form 16 June 2008; published August 2008
published online 1 July 2008

Abstract
Geodesic acoustic modes (GAM) are shown to constitute a continuous spectrum due to radial inhomogeneities. The importance and theoretical as well as experimental implications of this fact are discussed in this work. The existence of a singular layer causes GAM to mode convert to short-wavelength kinetic GAM (KGAM) via finite ion Larmor radii; analogous to kinetic Alfvén waves (KAW). Furthermore, it is shown that KGAM can be nonlinearly excited by drift-wave (DW) turbulence via 3-wave parametric interactions, and the resultant driven-dissipative nonlinear system exhibits typical prey-predator self-regulatory dynamics, consistent with recent experimental observations on HL-2A. The degeneracy of GAM/KGAM with beta-induced Alfvén eigenmodes (BAE) is demonstrated and discussed, with emphasis on its important role in the complex self-organized behaviors of burning plasmas.

PACS
52.35.Fp - Electrostatic waves and oscillations (e.g., ion-acoustic waves).
52.35.Mw - Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.).
52.35.Lv - Other linear waves.

© EPLA 2008