The transition phase between two nonlinear regimes of electron-beam–wave interaction
depending on the amplitude and the nature of the effective dissipation is
investigated with the help of numerical simulations. Effective dissipation due to
wave escaping to infinity out of the beam–wave interaction region as well as to collisions
in the background plasma is considered. If the dissipation is strong enough,
the evolution of the electron beam proceeds in a general way, independently of the
type of dissipation and of the nature of the considered waves: structures of strongly
concentrated electron bunches are formed. These bunches are not trapped in the
wave, and decelerate continuously owing to friction on waves: in the presence of
dissipation, the usual quasiperiodic exchange of energy between the wave and the
trapped particles, which prevents the wave from collapsing, does not occur. Considering
beam interaction with a finite number of waves (modulated wave packet), it
is shown that, if the dissipation is strong enough, the structure of electron bunches
is dynamically stable in a range of times exceeding several characteristic times of
their formation.
