Formation of solitons from the Langmuir waves with random phases

Abstract

The dynamics of the formation of Langmuir solitons from free Langmuir waves (plasmons) propagating at supersonic group velocities is described. The conservation laws and adiabatic restrictions which are imposed on the elementary processes with solitons containing supersonic plasmons are discussed. One-dimensional numerical results are presented which demonstrate that solitons appear both above and below the threshold of modulational instability. In the latter case, solitons are generated by the pressure fluctuations of plasmons belonging to the long-wavelength part of the spectrum. Analytical estimates are given of the characteristic time of plasmon trapping into solitons as well as of the number of trapped plasmons. Localization of plasmons caused by the acoustic perturbations can substantially change the rate of nonlinear spectral transfer of plasmons. Analytical estimates are compared with numerical results.