Spontaneous excitation of geodesic acoustic mode by toroidal Alfvén eigenmodes

Author: Qiu Zhiyong   Chen Liu   Zonca Fulvio  

Publisher: Edp Sciences

E-ISSN: 1286-4854|101|3|35001-35001

ISSN: 0295-5075

Source: EPL (EUROPHYSICS LETTERS), Vol.101, Iss.3, 2013-02, pp. : 35001-35001

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Abstract

Spontaneous nonlinear excitation of geodesic acoustic mode (GAM) by toroidal Alfvén eigenmodes (TAE) is studied within the framework of gyrokinetic theory. The dispersion relation for the parametric decays of a pump TAE mode into a TAE lower sideband and a GAM is derived. It is shown that, in the ideal MHD first stability region, the condition for spontaneous excitation of GAM by TAEs is ω20 > V2A/(4q2R20), in which, ω0 is the pump TAE real frequency, VA is the Alfvén speed, q is the safety factor and R0 is the torus major radius. The corresponding threshold condition is also derived and suggests the decay process as an effective saturation mechanism for TAE.