Saturation of energetic-particle-driven geodesic acoustic modes due to wave–particle nonlinearity. (18th December 2017)

• Record Type: Journal Article
• Authors: Biancalani, A.; Chavdarovski, I.; Qiu, Z.; Bottino, A.; Del Sarto, D.; Ghizzo, A.; Gürcan, Ö.; Morel, P.; Novikau, I.
• Is Part Of: Journal of plasma physics. Volume 83:Number 6(2017)
• Publication Date: 2017-12-18
• Subjects: fusion plasma, -- plasma nonlinear phenomena, -- plasma simulation; Plasma (Ionized gases) -- Periodicals; 530.4405
• DOI: 10.1017/S0022377817000976
• Languages: English
• ISSNs: 0022-3778

Abstract

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. As a main result, the formula for the saturation level is provided. 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.