Computer simulation on the electron beam-plasma interaction with application of high frequency external waves

One dimensional computer simulation on the non-linear interaction between the plasma oscillation excited by the primary beam and a high frequency signal coupled with the former oscillation in a low pressure discharge is done by using a particle-in-cell model, in order to understand the mechanism of the suppression phenomenon of noise. Coupling of the external signal is simulated in two ways: (i) the electric field is modulated and (ii) the beam velocity is modulated. Thus, the effects of an external signal in the actual experiment are studied. Temporal variation of electric field, wave spectra, and instantaneous and time-averaged velocity distributions of electrons are discussed for the above two cases. It is found that the phenomenon of suppression of the spontaneous wave by the external wave is due to the effect of velocity modulation while the field modulation does not lead to suppression but to parametric enhancement of the original wave. (author)