Nonlinear excitation of energetic-particle-driven geodesic acoustic mode by ions drift waves

Abstract

Nonlinear excitation of geodesic acoustic mode (GAM) by ions drift waves in the presence of energetic particles (EPs) is investigated through the hybrid model of fluid description and gyro-kinetic description, while the bulk ions temperature anisotropy and toroidal rotation are taken into account simultaneously. The coupling relation of EPs and the nonlinear effects on GAM is analytically derived and discussed. It is found that the nonlinear excitation can split inherent energetic-particle-driven GAM (EGAM) branches into different growth rates. For the intrinsic stable high frequency EGAM branch, the nonlinear effect generates a growth/damping rate. For the low frequency branches with inherent growth/damping rates due to the EPs, the nonlinearity cooperates with EPs in the excitation process.