Suppression of Two-Stream Instability by Beam Modulation

Abstract

Standing waves of longitudinal electron oscillation were observed in a beam-plasma system. By applying a density modulation to the beam, the amplitude of oscillation decreased to zero when the modulation frequency was near to those of the spontaneous oscillation. The modulation depth necessary for the oscillation to vanish was nearly proportional to the difference between the oscillation frequency and the modulation one. When the oscillation was suppressed, the oscillation having the same frequency as the modulation one was excited. These suppression and synchronization can be well explained by the assumption that the oscillation of electron density is described by the Van der Pol equation. Under this self-oscillator model the linear growth rate is evaluated and compared with the value calculated from the dispersion equation of the two-stream instability.