Saturation of energetic-particle-driven geodesic acoustic modes due to wave-particle nonlinearity

Abstract

The nonlinear dynamics of energetic-particle (EP) driven geodesic acoustic modes (EGAM) is investigated here. A numerical analysis with the global gyrokinetic particle-in-cell code ORB5 is performed, and the results are interpreted with the analytical theory, in close comparison with the theory of the beam-plasma instability. Only axisymmetric modes are considered, with a nonlinear dynamics determined by wave-particle interaction. Quadratic scalings of the saturated electric field with respect to the linear growth rate are found for the case of interest. The EP bounce frequency is calculated as a function of the EGAM frequency, and shown not to depend on the value of the bulk temperature. Near the saturation, we observe a transition from adiabatic to non-adiabatic dynamics, i.e., the frequency chirping rate becomes comparable to the resonant EP bounce frequency. The numerical analysis is performed here with electrostatic simulations with circular flux surfaces, and kinetic effects of the electrons are neglected.

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• On Zero Frequency Zonal Flow and Second Harmonic Generation by Finite Amplitude Energetic Particle Induced Geodesic Acoustic Mode
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Cited by in corpus (8)

• Kinetic theory of geodesic acoustic modes in toroidal plasmas: a brief review
• Nonlinear dynamics of energetic-particle driven geodesic acoustic modes in ASDEX Upgrade
• Gyrokinetic modelling of anisotropic energetic particle driven instabilities in tokamak plasmas
• Gyrokinetic investigation of the nonlinear interaction of Alfvén instabilities and energetic-particle driven geodesic acoustic modes
• Nonlinear velocity redistribution caused by energetic-particle-driven geodesic acoustic modes, mapped with the beam-plasma system
• Evidence of "Two Plasmon" decay of energetic particle induced geodesic acoustic mode
• Implementation of energy transfer technique in ORB5 to study collisionless wave-particle interactions in phase-space
• The enhanced soliton propagation and energy transfer in the coupled drift wave and energetic-particle-induced geodesic acoustic mode system