  Results are presented from experimental investigations of oscillatory
phenomena in an electron beam with a virtual cathode in a diode gap with a
decelerating field. Experiments have revealed a stochastic broadband generation
of the microwave oscillations of a virtual cathode in a decelerating field.
Numerical simulations based on a simple one-dimensional model have shown that
the onset of the stochastic generation and the broadening of the oscillation
spectrum with increasing beam deceleration rate are governed by the processes
of regrouping of the electrons in a beam with a virtual cathode.
