Nonlinear stage of ion-acoustic pack evolution in current plasma

Evolution of a quasi-monochromatic ion-acoustic packet in a collisionless current-carrying plasma has been considered. A small difference between group and phase velocities leads to a number of special of process. In particular, the resonance particles that are reflected from the front of the packet play an essential role. The evolution equations have been obtained to describe the nonlinear stage of the process for the oscillation frequency of trapped particles greater than the rate of change of amplitude. It is found that the modulation instability is developed by untrapped particles for comparation instability is developed by untrapped particles for comparatively small amplitudes of the packet. This instability results in packet splitting into widely spaced short perturbations. Numerical simulation data and experimental results are discussed