Excitation of zonal flow by nonlinear geodesic acoustic mode

Abstract

The zero frequency zonal flow (ZFZF) excitation due to the nonlinear geodesic acoustic mode (GAM) is investigated in the framework of gyro-kinetic equations, which were first investigated by Chen et al. [Europhys. Lett. 107, 15003 (2014)]. We show that after integrating over the velocity space, the first order finite orbit width (FOW) term of nonlinear GAM disappears, and hence, the second order FOW term should be taken into account to generate the ZFZF. The anisotropy of the equilibrium is also considered.