Computer Simulation of Modulational Instability for the Electron Plasma Wave

Modulational instabilities for the electron plasma wave are studied by computer simulation based on the fluid equations for the electron and ion. The growth rate and frequency shift given by the simulation are in agreement with the theoretical predictions by Fried et al. in the wavenumber regions for both k o ≪γ -1/2 and k o γ -1/2 , where k o and γ are the normalized carrier wavenumber and mass ratio respectively. Although an envelope soliton is produced at the saturation state of the instability, a coupled soliton is not observed. The tails of ion density are excited, whenever the half width of the soliton is a little less than 10λ De , where λ De is the electron Debye length. Therefore, such a width, often observed in laboratory experiments, is explained by the generation of the tails.