A numerical simulation of an O-type backward-wave oscillator (BWO) operatin
g under nonlinear conditions is presented. It is demonstrated that the dyna
mics is characterized by an intricate sequence of oscillation regimes with
multiple transitions between order and chaos according to different scenari
os. The connection between the bifurcations and bunching-debunching process
es is studied. The nonlinear dynamics at finite values of the Pierce gain p
arameter is discussed.