  Results are presented from numerical modeling of the effect of the
inhomogeneity of the ion background on the complicated spatiotemporal dynamics
of an electron beam with a virtual cathode in plane geometry. The possibility
is demonstrated of increasing the generation frequency without changing the
beam current. The spatiotemporal structures that form in the beam and govern
the complicated stochastic dynamics of the nonuniform electron-plasma system
under consideration are investigated by the methods of wavelet bicoherence and
by analyzing the calculated electron trajectories on the space-time diagrams
