K. Yu. Vagin

Amplification of electromagnetic radiation by a nonequilibrium plasma unstable against the development of Weibel instability

The reflection of an electromagnetic pulse by a nonequilibrium plasma in which the development of Weibel instability is possible has been studied. An exponentially strong amplification of the reflected signal at the stage of instability development has been found to be possible. The amplification maximum takes place at a radiation frequency comparable to the instability growth rate. A nonequilibrium plasma is shown to be a generator of radiation even after the switch-off of the incident pulse. The described effect of amplification of the reflected signal points, in particular, to a new possibility in mastering the terahertz frequency band.

On the growth rate of aperiodic instability in plasma with an anisotropic bi-Maxwellian electron velocity distribution

The growth rate of aperiodic instability of transverse and longitudinal-transverse electromagnetic field perturbations in plasma with an anisotropic bi-Maxwellian electron velocity distribution is studied. The boundaries of the instability domains in wave vector space are found, and the growth rates of field perturbations with configurations different from that corresponding to the maximum growth rate are determined.

Reflection of electromagnetic radiation from plasma with an anisotropic electron velocity distribution

The reflection of a test electromagnetic pulse from the plasma formed as a result of tunnel ionization of atoms in the field of a circularly polarized high-power radiation pulse is analyzed using the kinetic approach to describe electron motion. It is shown that the reflected pulse is significantly amplified due to the development of Weibel instability. The amplification efficiency is determined by the maximum value of the instability growth rate, which depends on the degree of anisotropy of the photoelectron distribution function.

Leaky unstable modes and electromagnetic radiation amplification by an anisotropic plasma slab

The interaction between electromagnetic radiation and a photoionized plasma slab with an anisotropic electron velocity distribution is studied. It is shown that the fields of leaky modes are amplified due to the development of aperiodic instability in the slab, which leads to an increase in both the reflected and transmitted fields. The transmitted field can significantly increase only if the slab thickness does not exceed the ratio of the speed of light to the electron plasma frequency, whereas there is no upper bound on the slab thickness for the reflected signal to be amplified.

Electromagnetic radiation from a plasma slab during the development of Weibel instability

Electromagnetic radiation from an anisotropic plasma slab formed by ionization of matter in the field of a high-power femtosecond pulse is studied. It is shown that the growth of initial field perturbations in the course of Weibel instability is accompanied by the generation of nonmonochromatic radiation with a characteristic frequency on the order of the instability growth rate. It is found that perturbations with characteristic scale lengths less than or on the order of the ratio of the speed of light to the Langmuir frequency are excited and radiated most efficiently, provided that the slab is thicker than this ratio.

Potential surface waves in anisotropic plasma

The dependences of the frequency and damping rate of a potential surface wave on the wavenumber and the degree of anisotropy of a bi-Maxwellian electron distribution characterized by different temperatures along and across the plasma surface are established. It is demonstrated that the influence of electron thermal motion along the plasma surface on the surface wave properties is similar to the influence of thermal motion on the properties of a bulk Langmuir wave. On the contrary, thermal motion across the surface qualitatively affects the dispersion relation and substantially increases the damping rate.

Stimulated Brillouin scattering in a dusty plasma

A kinetic description is developed for stimulated Brillouin scattering (SBS) in a dusty plasma with negatively charged dust grains. The threshold for SBS and the width of its spectral line are determined in the limits of weak and strong damping of the dust ion acoustic waves involved into the scattering process. For different mechanisms of the dissipation of dust ion acoustic waves, the threshold for SBS and the width of its spectral line are obtained as functions of the dust grain charge and the dust number density.

High-Frequency Quasi-Potential Waves in the Plasma Formed under Tunnel Ionization of Atoms

The dispersion law and collisionless damping rate of quasi-potential waves in the plasma formed upon tunnel ionization of gas atoms in the field of a short pulse of circularly or linearly polarized radiation are found. It is shown how the frequency and damping rate of quasi-potential waves depend on the wave propagation direction relative to the symmetry axis of the photoelectron distribution. It is established that, in plasma with a toroidal photoelectron velocity distribution, weakly damped waves with a linear dispersion law and frequency above the electron plasma frequency can propagate in a wide range of angles. In the case of a bi-Maxwellian photoelectron distribution, the frequency of weakly damped waves is comparable with the electron plasma frequency and the anisotropy of electron motion manifests itself in relatively small corrections to the dispersion law.

Nonlinear spectral properties of stimulated Brillouin scattering in plasma

New phenomena in which the stimulated Brillouin scattering (SBS) changes the number and magnitude of frequency shifts in a plasma upon a nonlinear increase in the pumping field intensity are discovered. It is found that the SBS becomes forbidden and then allowed again (upon a subsequent increase in the pumping intensity).

Stimulated Brillouin scattering in a plasma with ion-acoustic turbulence

A theory of stimulated Brillouin scattering (STBS) in a plasma with ion-acoustic turbulence is developed using concepts of parametric instability under conditions when equations of two-temperature hydrodynamics can be used to describe ion-acoustic perturbations of the electron density. The temporal growth rate of the absolute instability and the spatial gain of the scattered wave are determined. The dependence of the threshold density of the radiation flux on the angle between the scattering wave vector and the direction of anisotropy of the turbulent noise is described. A new effect of STBS forbiddenness caused by anomalous turbulent heating of the ions is predicted for a plasma with a high level of turbulent noise.