  Nonlinear self-interaction of finite amplitude energetic particle induced
geodesic acoustic mode (EGAM) is investigated using nonlinear gyrokinetic
theory. It is found that both zero frequency zonal flow(ZFZF) and second
harmonic can be driven by finite amplitude EGAM, with energetic particles (EPs)
playing a dominant role in the nonlinear couplings through finite orbit width
effects. For ZFZF, the effects of EPs on EGAM nonlinear self-coupling dominate
that of the thermal plasmas which are also present; while the second harmonic
generation is only possible via finite amplitude coupling though EPs. Our
findings may improve the understanding of stabilizing zonal modes, and
consequently, drift wave turbulence.
