Regimes and spectra of čerenkov beam instability in a nonlinear plasma

Abstract

We study the nonlinear evolution of an arbitrary initial disturbance due to the development of Cerenkov beam instability in a magnetized plasma-beam system of finite transverse size. Singleparticle, collective, and aperiodic regimes of this instability are considered. We calculate the nonlinear spatial spectra of the waves excited at different development stages of the beam instability in a plasma for the cases of quasi-monochromatic, pulsed, and noise initial disturbances. We analyze the formation and decay of regular structures in the beam and plasma at the developed nonlinear stage of the process. We find that plasma nonlinearity leads to the transfer of disturbance energy to the short-wave region of the spectrum. We show that, due to the development of beam instability, noise initial disturbance tends to become more monochromatic, whereas the shape of a pulsed one tends to remain unchanged. Transformation of monochromatic spatial disturbances into quasi-monochromatic plasma waves due to the instability development is analyzed.