Özet:

It is shown, the modulation instability processes of long-wave Langmuir oscillation in hot and cold plasmas are possessed such a symmetry and mechanism of short-wave oscillation excitation. The maximum of the growth rate of the instability in cold plasma moves in short-wave part of spectrum, in hot plasma the growth rates in all over the spectral region are reduced, if the amplitude of pump wave has decreased. The value of the growth rate maximum in cold plasma in this case not changes, but in hot plasma similar value decreases. The energy motion along the spectrum is due to mode coupling and in cold plasma the drift of the growth rate maximum, in hot plasma – large-scale increments in short-wave part of spectrum. The spatial symmetry of ions perturbation is associated with such symmetry type of field and electrons perturbation. The amplitude of standing wave structure, which is appeared in that case, is increasing and the half-width of it is reducing in initial stage of the instability. When such symmetry is absent, the field and the density deformation are formed at the expense of the interference of different scale perturbation.

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