Simultaneous Suppression of an Electron Plasma Wave and an Ion Acoustic Wave by Beam Modulation

An electron plasma wave of an axial mode and an ion acoustic wave of a radial mode were spontaneously excited in a beam-plasma system. By applying the density modulation to the beam at the frequency near to that of the electron plasma wave, the electron plasma wave and the ion acoustic wave faded out simultaneously. Suppression phenomenon of electron plasma wave is now well explained. Simultaneous suppression of the ion acoustic wave implies that this wave is originated from the electron plasma wave.