Propagation of Nonlinear Ion Acoustic Wave with Generation of Long-Wavelength Waves

The nonlinear propagation of the wave packet of an ion acoustic wave with wavenumber k₀≈k_De (the electron Debye wavenumber) is investigated by computer simulations. From the wave packet of the ion acoustic wave, waves with long wavelengths are observed to be produced within a few periods for the amplitude oscillation of the original wave packet. These waves are generated in the region where the original wave packet exists. Their characteristic wavelength is of the order of the length of the wave packet, and their propagation velocity is almost equal to the ion acoustic speed. The long-wavelength waves thus produced strongly affect the nonlinear evolution of the original wave packet.