Relaxation of a relativistic electron beam in plasma in the trapping regime

A model for collective relaxation of high-power relativistic electron beams in plasmas is proposed, which describes beam-plasma interaction in the regime when amplitudes of unstable waves are large enough to trap beam electrons. The distinctive feature of this regime is that the power lost by beam electrons as they interact with exited wave packets weakly depends on the energy of these packets. This makes the model insensitive to the nature of nonlinear processes in plasma, which are responsible for saturation of the beam instability. The model is thus rather universal and suitable for quantitative comparison with the experimental data. The predicted profiles of energy release along the plasma column are in a good quantitative agreement with the ones measured at various experimental facilities.