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

A. Biancalani (1) , I. Chavdarovski (1) , Z. Qiu (2) , A. Bottino (1) , D. Del Sarto (3) , A. Ghizzo (3) , Özgür D. Gürcan (4) , Pierre Morel (4) , I. Novikau (1)

1 IPP - Max-Planck-Institut für Plasmaphysik [Garching]
2 Zhejiang University
3 IJL - Institut Jean Lamour
4 LPP - Laboratoire de Physique des Plasmas

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.

Domaines: Physique des plasmas [physics.plasm-ph]; Physique de l'espace [physics.space-ph]; Dynamique des Fluides [physics.flu-dyn]; Physique mathématique [math-ph]; Physique des Hautes Energies - Théorie [hep-th]; Dynamique Chaotique [nlin.CD]; Calcul parallèle, distribué et partagé [cs.DC]

A. Biancalani, I. Chavdarovski, Z. Qiu, A. Bottino, D. Del Sarto, et al.. Saturation of energetic-particle-driven geodesic acoustic modes due to wave–particle nonlinearity. Journal of Plasma Physics, 2017, 83 (6), pp.725830602. ⟨10.1017/S0022377817000976⟩. ⟨hal-01791835⟩