Yu. V. Kirichenko

Plasma travelling wave antenna

The possibility of using plasma column as linear travelling wave antenna is studied. It is shown that surface current waves propagating in plasma column of finite length are a source of paraxial electromagnetic radiation of decimeter band. Influence of dielectric waveguide, which surrounds cold isotropic plasma, on dispersion properties of plasma column is investigated. The corresponding dispersion equation for eigenwaves of circular dielectric waveguide filled with plasma is derived and solved numerically. Plasma and waveguide parameters are determined under which the surface wave slowing-down is close to unity leading to antenna’s radiation primarily in axial direction. It is shown that in case of plasma density around 1012−1013 cm−3 dispersion of the considered wave is close to dispersion of waves propagating in metal travelling wave antenna.

Axial-radiation plasma antenna

The possibility of applying a cylindrical isotropic collisionless plasma column with a thin dielectric shell as an antenna of strictly axial radiation is investigated. It is assumed that the phase velocity of radiated waves approaches the velocity of light and the radiated wavelength substantially exceeds the radius of the antenna. Radiation patterns of azimuthally symmetric and azimuthally nonsymmetric current waves are calculated. It is shown that, in contrast to the symmetric wave used in traditional traveling-wave antennas, the first harmonic of a nonsymmetric current wave in plasma is a source of radiation reaching its maximum at the zero angle to the antenna’s axis.

Study of a longitudinally nonuniform plasma layer

Transformation of the energy of surface waves in a plane plasma layer with a longitudinal irregularity of density is studied by the method of spectral decomposition. The total field is represented by an expansion in surface and pseudo-surface waves. A system of integro-differential equation for the coefficients of expansion determining the amplitudes of the transmitted, reflected, and scattered waves is obtained. It is shown that, in some special cases, this system of equations is reduced to a system of ordinary differential equations even if the plasma density rapidly changes. The fraction of the energy of surface waves that transforms into radiation at an acute angle with the layer can reach 50–60%.

Microwave radiation of cylindrical plasma column

The travelling wave antennas representing a column of isotropic plasma and a plasma column placed into external infinitely large magnetic field have been theoretically and numerically investigated and compared. The relationships of radiation patterns as a function of the plasma density, geometrical parameters of the plasma cylinder and the radiation wavelength were also investigated. We considered both the linear antennas and the radiating antennas with wavelengths close to the antenna radius. An axially symmetric E-wave was studied. The need of taking into account the radial distribution of antenna current was shown. The dependence of normalized radiation patterns on the wave-slowing was analyzed. The characteristic value of plasma density was found; if this value is exceeded, the normalized radiation patterns are sharp directional and have the main lobe located at small angle towards the antenna axis. For the magnetized plasma this characteristic value of density is much smaller than for the isotropic one. With the rise of the plasma density the level of side lobes gets smaller.

Radiation from a Plasma Layer with a Strong Longitudinal Irregularity

The efficiency of conversion of the energy of a surface wave into radiation at longitudinal irregularities of a planar plasma layer is studied. The analysis is performed by the spectral expansion of the field in a complete set of surface and pseudosurface waves. The system of integro-differential equations for the coefficients of expansion that determine the amplitudes of the transmitted, reflected, and scattered waves as well as the radiation pattern is solved in the case of a rapid change in the plasma density. The coefficients of transformation of energy into the energy of radiation as functions of the gradient of the plasma density for different values of the electrical length of the region of plasma irregularity and the electric thickness of the plasma layer are found. Examples are demonstrated when the fraction of the energy of the surface wave transformed into radiation reaches 60–70%. Radiation patterns that proved to be highly directional and having one lobe with the maximum at an angle of a few degrees to the direction of propagation of the surface wave are calculated.

Generation and amplification of electromagnetic waves by an annular electron beam in a radial electric field in free space

Mechanisms for the generation and amplification of electromagnetic waves by a thin-walled annular beam of electrons rotating in a radial electric field in free space are studied theoretically. It is shown that electromagnetic waves can be generated and amplified under the Cherenkov resonance conditions. The frequencies and growth rates of the generated waves are determined, and the propagation characteristics and amplification coefficients of the amplified waves are found.

Cylindrical Plasma Antenna with Large Longitudinal Density Irregularity

The efficiency of operation of a cylindrical plasma antenna as a function of the degree of longitudinal nonuniformity of the plasma density is examined. The study is based on the method of spectral field expansion into a complete set of functions comprising surface and pseudosurface waves of the plasma column. The system of integrodifferential equations for expansion coefficients determining radiation patterns and the amplitudes of transmitted, reflected, and scattered waves is solved in the case of rapid variation in the plasma density. Dependences of the coefficients of conversion of the surface-wave energy on the plasma-density gradient, the electric length of the section of plasma nonuniformity, and the electric radius of the plasma cylinder are calculated. It is demonstrated by examples that the portion of energy of the surface wave converted into radiation may exceed 50%. It has been found that the radiation patterns are narrow with a single lobe whose maximum is at an angle of several degrees to the direction of propagation of the surface wave. As the plasma-density gradient increases, the lobe width decreases and the lobe itself shifts toward 0°.

Plasma antenna of traveling wave with axial radiation

The dispersion equations for azimuthally asymmetric slow waves propagating along the plasma column, located in the dielectric cylinder are derived and solved. These waves induce currents that lead to the radiation of electromagnetic waves into the surrounding space. The antenna, which is a hollow dielectric cylinder of finite length, filled with an isotropic cold collisionless plasma is considered. The formulas for the angular distribution of the radiation in the far-field for azimuthally asymmetric and azimuthally symmetric slow current waves propagating along the antenna are derived. They can be used for case when the antenna length is much greater than antenna transverse dimensions and the radiated wave length. At that antenna radius, the thickness of the dielectric tube and dielectric permittivity, plasma density, the phase velocity and the wave current frequency can be arbitrary. Practically interesting case of a linear antenna of a traveling wave, which phase velocity is close to the speed of light is considered. Asymmetrical current wave with m=1 has a particular place. For it the maximum of directional diagram (pattern), unlike the asymmetric waves (m>1) and the symmetric wave (m=0), accounts for the direction of the antenna axis, and the side-lobe level is much lower than for the symmetric wave. The width of the pattern is decreased with increasing the ratio of the antenna length to the radiated wave length L/λ and is 17° for L/λ=10 and 12° for L/λ=20. Thus, the plasma antenna operating in the regime of the asymmetric wave current with m=1, can serve as a source of strictly axial radiation. It is shown that a sufficiently thin dielectric shell does not influence on the normalized radiation pattern.

Microwave radiation of the column of isotropic and magnetized plasma

In this paper the antenna of a traveling wave, which represents a column of isotropic plasma or the plasma column, placed in an external infinitely large magnetic field is studied both theoretically and numerically and compared between them. Plasma is assumed cold and collisionless. The dependence of radiation patterns upon plasma density, geometric parameters of plasma cylinder and radiation wavelength is investigated. At that it is considered not only linear, but also short-wave antenna radiating wavelengths close to the antenna radius. In an isotropic plasma column (B0 = 0) and in the magnetized (B0 = ∞), there are only a slow plasma E-wave with frequencies lower the plasma frequency. We study axially symmetric E-wave. Solutions of the dispersion equations give the dependence of the frequency on the wavevector, necessary to calculate the radiation patterns. The wave in plasma cylinder induces a wave of current density. Knowing the current it is possible to calculate the radiation field in the far field and, accordingly, the normalized radiation pattern.

Dynamics of the transverse oscillations of an electron beam in a tellarator

The transverse oscillations of a thin electron beam in a stellarator or in a modified betatron were theoretically studied. The analysis is based on the relativistic Lorentz equation for intrinsic fields of the electron beam calculated by the method of retarded potential. Conditions for an instability development caused by the stellarator field inhomogeneity are determined. It is shown that a stellarator may also feature other instabilities of the transverse oscillations which are not related to the stellarator field inhomogeneity.