Sergey I. Popel

Ion-acoustic solitons in electron--positron--ion plasmas

The ion‐acoustic solitons are investigated in three‐component plasmas, whose constituents are electrons, positrons, and singly charged ions. It is found that the presence of the positron component in such a multispecies plasma can result in reduction of the ion‐acoustic soliton amplitudes.

Shock waves in plasmas containing variable‐charge impurities

Shock structures in plasmas containing variable‐charge macro particles are shown to exist because of an effective dissipation associated with charging of the latter.

Modulational interactions in plasmas

1: Modulational Interactions in Physics. 2: Modulational Interaction of Potential Electric Fields. 3: Higher Nonlinearities. 4:Strongly Nonlinear Plasma Waves. 5: Excitation of Magnetic Fields. 6: Homogeneous Plasmas in External Magnetic Field. 7: Bounded and Inhomogeneous Plasmas in External Magnetic Field. 8: Instabilities in Collisional Plasmas. 9: Instabilities of Surface Waves. 10: Two Monochromatic Pump Waves. 11: Modulational Processes and Weak Plasma Turbulence.

Theory of modulational interactions in plasmas in the presence of an external magnetic field

Abstract In many real physical and astrophysical situations, an external magnetic field is present. The magnetic field results in a variety of specific plasma modes and leads to an anisotropic distribution of plasma oscillations. The present review reflects the present state of the theory of modulational interactions in magnetized plasmas. Modulational interactions are considered on the basis of a simple and universal approach using new methods developed for the description of modulational effects in arbitrary media. This approach enables us to visualize the physical processes occurring in plasmas in the presence of modulational interactions. Emphasis is given to the role of modulational interactions in processes of particle acceleration, generation of current drive, physical phenomena in the Earths magnetosphere and in active geophysical and space experiments. The influence of boundary conditions and plasma inhomogeneity is considered in detail. These effects can essentially change the dispersion properties of plasma modes, and their influence can be even more significant than effects of plasma anisotropy (caused by the external magnetic field) or thermal corrections to the dielectric permittivity tensor. Modulational interaction is the most important nonlinear process for waves excited as a result of the lower-hybrid drift instability; in particular, the modulational interaction determines the saturation mechanism for this instability which in turn enables us to obtain the effective collision frequency and to estimate the width of the Earths magnetopause region. The theory of modulational interactions is presented for the explanation of magnetic structures, particle spectra, and the electric field amplitude observed in active geophysical experiments.

Electrostatic solitons in an electron–positron plasma with two distinct groups of positrons

The existence of novel electrostatic solitary pulses in an electron-positron plasmas with two distinct groups of positrons is demonstrated. It is found that the soliton potential can assume both the rarefactive and compressive polarities. The results might be useful in understanding the properties of localized disturbances in astrophysical plasmas.

Modulational instability of Langmuir wave packets

The broad spectra of random waves in unmagnetized plasmas are considered. A universal nonlinear formalism is developed for description of the nonlinear effects (modulational instability, etc.) in which random plasma waves take part. The integral equations for perturbations of wave field correlation functions are obtained. In a description of the modulational instability of random wave packets these equations play the same role as the set of coupled equations for the fields of modulational perturbations in the case of a single monochromatic pump wave. On the basis of these integral dispersion equations the modulational instability of broad wave spectra is investigated for the one‐dimensional situation (when directions of propagation of the random waves coincide with that of the modulational perturbations) and for isotropic wave turbulence.

Finite amplitude waves in ion-beam plasma systems

Abstract Several types of solitary waves can exist in an ion-beam plasma system. Their velocity is determined as a function of the beam velocity and the wave amplitude θ 0 . The region of existence is limited for θ 0 → 0 by the linear modes, and for finite θ 0 by the trapping of the beam or background ions.

Plasma equations in general relativity

Vlasov’s equation and the ideal multifluid equations are considered in manifestly covariant form. In the latter case, a thermodynamic closure (locally the first law of thermodynamics) leads to a generalized Kelvin/Helmholtz theorem. In the former case, the local dispersion relation for Langmuir waves in a strong gravitational field is derived and solved.

A three‐circulation theorem for relativistic plasmas

It is shown that the sum of three circulations (hydrodynamic, magnetic, and thermal) is constant in time for each component of a perfect relativistic plasma. A constraint for the initial configuration (‘‘Weber/Ertel case,’’ the lines of canonical vorticity lie on surfaces of constant entropy) leads to zero potential vorticity also for later times; this is generally realized in inhomogeneous flow equilibria for which the explicit time‐dependence of Clebsch potentials is given. Equilibrium states of warm relativistic plasmas with vanishing thermal circulation are discussed.

Physical aspects of the plasma-maser interaction

Abstract The plasma-maser interaction of Langmuir waves with ion-acoustic waves and electrons of a plasma and a beam is considered. It is found that the maximum rates of the plasma-maser instability are connected with the stochastic properties of the nonresonant ion-sound turbulence and those of the resonant Langmuir waves. The condition for dominance of te plasma-maser effect over the linear Landau instability is obtained. The physical aspects of the plasma-maser interaction are discussed.