  Numerical simulations of Alfv\'en modes (AM) driven by energetic particles
are performed with the GK global PIC code ORB5. A reversed shear equilibrium
magnetic field is adopted. A simplified configuration with circular flux
surfaces and large aspect ratio is considered. The nonlinear saturation of
beta-induced Alfv\'en eigenmodes (BAE) is investigated. The roles of the
wave-particle nonlinearity of the different species, i.e. thermal ions,
electrons, and energetic ions are described, in particular for their role in
the saturation of the BAE and the generation of zonal flows. The nonlinear
redistribution of the electron population is found to be important in
increasing the BAE saturation level and the zonal flow amplitude.
