Frequency Shift of an Electron Plasma Oscillation in a Modulated Beam-Plasma System

Abstract

A spontaneous electron plasma oscillation in a beam-plasma system can be suppressed by modulating the beam density. In this case small shift of frequency of the oscillation is observed. At the same time oscillations with frequencies 2ω−ω_m and 2ω_m−ω arise, where ω is the frequency of the spontaneous oscillation and ω_m is the modulation frequency. However, oscillations having frequencies ω_m+ω and |ω_m−ω| are not detected. These phenomena are interpreted on the basis of van der Pol equation with a driving term, and a good agreement is found between the theory and the experiment.