Observation of the event on 16 May, 1981 in the optical and kilometer ranges

Charge density waves play the essential role on electrodynamics of a plasma and dense electron beams. They have important application in SHF-radiation generation, beam transport and collective acceleration methods. It is shown that the theory of charge density waves in high-current electron beams can be only a relativistic theory. The dispersive properties of linear and nonlinear charge density waves in such beams are investigated. It is found, in particular, that the si dispersion of a slow wave depends strongly on its amplitude. The excitation of a slow wave in a high-current beam on development of a Cherenkov instability of the simple decay type is considered. The existence of two instability saturation mechanisms is mentioned. For currents bellow the limiting vacuum current the mechanism consists in trapping and strong turbulence of the beam. For high currents it consists in a nonlinear frequency shift without any randomization of the beam. The dependence of the beam emission efficiency on the current is investigated. In the ultrarelativistic limit the efficiency is calculated analytically