  Energetic particles produced by neutral beams are observed to excite
energetic-particle-driven geodesic acoustic modes (EGAMs) in tokamaks. We study
the effects of anisotropy of distribution function of the energetic particles
on the excitation of such instabilities with ORB5, a gyrokinetic
particle-in-cell code. Numerical results are shown for linear electrostatic
simulations with ORB5. The growth rate is found to be sensitively dependent on
the phase-space shape of the distribution function. The behavior of the
instability is qualitatively compared to the theoretical analysis of dispersion
relations. Realistic neutral beam energetic particle anisotropic distributions
are obtained from the heating solver RABBIT and are introduced into ORB5 as
input distribution function. Results show a dependence of the growth rate on
the injection angle. A qualitative comparison to experimental measurements is
presented and few disagreements between them are found, being the growth rate
in the simulations much lower than that from experiments. An explanation for
the difference is advanced.
