Magnetic helicity tensor for an anisotropic turbulence

The evolution of the magnetic helicity tensor for a nonzero mean magnetic field and for large magnetic Reynolds numbers in an anisotropic turbulence is studied. It is shown that the isotropic and anisotropic parts of the magnetic helicity tensor have different characteristic times of evolution. The time of variation of the isotropic part of the magnetic helicity tensor is much larger than the correlation time of the turbulent velocity field. The anisotropic part of the magnetic helicity tensor changes for the correlation time of the turbulent velocity field. The mean turbulent flux of the magnetic helicity is calculated as well. It is shown that even a small anisotropy of turbulence strongly modifies the flux of the magnetic helicity. It is demonstrated that the tensor of the magnetic part of the alpha effect for weakly inhomogeneous turbulence is determined only by the isotropic part of the magnetic helicity tensor.     

Nichtlineare Wechselwirkung elektromagnetischer Wellen im Plasma mit konstantem Magnetfeld

The nonlinear interaction of waves in anisotropic plasmas is considered. Solving the hydrodynamics equations with a n-th order perturbation procedure, an equation for the nonlinear electric field is derived. The n-th order current produced by interaction of waves with lower order is represented by means of a nonlinear tensor of conductivity, which is calculated for n = 2. It is shown, that a miced plasma wave with combination frequencies is excited as the result of interaction of two transverse (ordinary) waves propagating perpendicular to the magnetic field.     

离子声波对电子输运的影响

从Balescu-Lenard碰撞项出发,得到了电子-电子通过交换离子声波对碰撞的贡献项,并计算了电子输运(热导)系数.计算结果表明,由于离子声波的作用电子热导系数有所下降 关键词： 电子输运 离子声波 Balescu-Lenard方程     

Propagation of radiation in a plasma situated in a gravitational field

Weak electromagnetic and gravitational fields in a plasma situated in a strong gravitational field, are studied using linearized, general-relativistic, kinetic equations. A tensor operator is constructed for the electrical conductivity of a plasma in a gravitational field, which is a general-relativistic generalization of the electrical conductivity of a homogeneous plasma. Similar tensor operators, which allow one to determine the energy-momentum tensor and the vector current, induced by electromagnetic and gravitational fields in a plasma, are also obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 57–62, September, 1976.     

Temperature Effects on the Beat Heating of a Collisional Magnetoplasma

The beat heating of a magneto-plasma by two antiparallel electromagnetic waves at different temperatures is examined. The effects of plasma temperature, plasma electron collisions, plasma ion collisions and magnitude and direction of the magnetic field on the excitation of plasma electron waves and plasma ion waves are studied. A formula for the power absorption density of the plasma by using Maxwell's equations in conjuction with continuity and momentum equation. including collisions and pressure tensor terms, is derived. The contribution of the plasma temperature to the power absorption density, both at low and high beat frequencies, of the collisional and the non-collisional magnetised plasmas is found very significant and is illustrated numerically. The inclusion of pressure tensor term in the momentum equation is also found to cause characteristic changes in the power absorption density of the plasma with the orientation of magnetic field.     

Lorentz-boosted evanescent waves

Polarization, spin, and helicity are important properties of electromagnetic waves. It is commonly believed that helicity is invariant under the Lorentz transformations. This is indeed so for plane waves and their localized superpositions. However, this is not the case for evanescent waves, which are well-defined only in a half-space, and are characterized by complex wave vectors. Here we describe transformations of evanescent electromagnetic waves and their polarization/spin/helicity properties under the Lorentz boosts along the three spatial directions.     

Plane Waves Propagating in Chiral Plasma and Chiral Ferrite Media

Plane wave propagation in chiral plasma and chiral ferrite media is studied in kDB coordinate system. General wave equations and characteristic equations of plane waves propagating along an arbitrary direction in chiral plasma and in chiral ferrites are derived in simple formulations respectively. Four wavenumbers and their corresponding dispersion characteristics are resulted for propagation both along and normal to the biasing magnetic field. When plane wave with negative helicity propagates along the biasing magnetic field in chiral ferrites, backward waves emerge. However backward waves occur with both positive and negative helicities when propagating along the biasing magnetic field in chiral plasma.     

Dispersion process of electromagnetic waves in a moving medium

The propagation of electromagnetic waves in a moving isotropic plasma and in a moving magnetoactive plasma is considered using the invariant methods of tensor analysis. Expressions are obtained for the dielectric permittivity tensor, the dispersion equations, and the refractive indexes of electromagnetic waves in these media. Using these results it is possible to establish corrections to the angular displacement which occurs when radiation passes through a moving electron plasma.Published from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 1, pp. 121–129, January, 1996.     

Relativistic calculation of the two photon coupling of scalar and tensor mesons

The decay rates of scalar and tensor mesons into two photons are calculated in the Bethe-Salpeter bound state formalism. The suppression of the non-relativistic estimates due to relativistic kinematics is found to be substantial. Production crosssections in colliding beam experiments are estimated to be in the picobarn range. Also in the relativistic case the helicity 0 production cross-section of tensor mesons is found to be negligible.     

Spin-2 Fields and Helicity

By considering the irreducible representations of the Lorentz group, an analysis of the different spin-2 waves is presented. In particular, the question of the helicity is discussed. It is concluded that, although from the point of view of representation theory there are no compelling reasons to choose between spin-2 waves with helicity σ=±1 or σ=±2, consistency arguments of the ensuing field theories favor waves with helicity σ=±1.     

Analysis of long wavelength electromagnetic scattering by a magnetized cold plasma prolate spheroid

Abstract

Using dielectric permittivity tensor of the magnetized prolate plasma, the scattering of long wavelength electromagnetic waves from the mentioned object is studied. The resonance frequency and differential scattering cross section for the backward scattered waves are presented. Consistency between the resonance frequency in this configuration and results obtained for spherical plasma are investigated. Finally, the effective factors on obtained results such as incident wave polarization, the frequency of the incident wave, the plasma frequency and the cyclotron frequency are analyzed.     

The effect of local rotations on the electromagnetic properties of plasma

Local rotations of plasma change the mean electromagnetic characteristics of plasma even in the absence of average rotation. The effective permittivity tensor of plasma differs from that calculated without taking into account local rotations. The dispersion curve for longitudinal oscillations is also changed. For the transverse component of the dielectric tensor, the threshold frequency for small k is about 2.2 times greater than that calculated without taking into account rotations. Local rotations also affect the electric conductivity and the electron thermal conductivity. The fluctuations of the directions of local rotations reduce the coherent intensity.     

THE THEORETICAL INVESTIGATION OF THz ELECTROMAGNETIC WAVES IN A ROD DEGENERATE PLASMA-WAVEGUIDE

By using the Fourier components of dielectric tensor elements of cold collisionless degenerate plasmas, the dispersion relation of electromagnetic waves in a cylindrical metallic waveguide with a degenerate plasma column protected by an annular dielectric layer are obtained. The permissible frequency regions for slow and fast waves in E-mode (TM) are presented. Furthermore, the graph of cutoff frequency versus the radius of plasma column for the fast waves is investigated. In addition, the time growth rate for excitation of symmetric slow E-modes (TM) by a thin annular relativistic electron beam (TAREB) is studied. The graph of time growth rate respect to radius of dielectric layer and accelerating voltage are presented. PACS No. 52.25.     

Excitation of an Additional Region of Short-Wavelength Plasma Oscillations in Ionospheric Heating Experiments

We discuss transfer of plasma waves, excited by a powerful radio wave due to its scattering on artificial ionospheric irregularities, into an additional region of very short plasma oscillations polarized almost perpendicular to the magnetic field. Such a region can exist in the magnetized ionospheric plasma due to the strong spatial dispersion. We take into account the plasma-wave diffusion over the spectrum caused by multiple scattering on irregularities, as well as the nonlinear process of plasma-wave interaction due to induced scattering by ions. The latter process leads to the transfer of primary plasma waves into the additional region. The induced scattering is considered in the differential approximation valid for sufficiently smooth plasma-wave spectra. The numerical calculations are performed for a Maxwellian plasma in which suprathermal electrons are absent. It is shown that in this case, the additional region of plasma waves is excited if the pump frequency is close to but slightly less than the fourth electron gyroharmonic, so that the absorption of primarily excited plasma waves becomes sufficiently strong. Application of our calculations to the results of ionospheric experiments is discussed.     

High-frequency conductivity of a two-dimensional electron gas with impurity electron states

The high-frequency conductivity tensor for a two-dimensional electron gas with short-range-acting impurity atoms has been computed. Spatial dispersion of the conductivity was taken into account. The threshold and maxima of the dissipative part of the conductivity arising from ionization of the impurity atoms by the field of electromagnetic waves were found. Numerical calculations of the conductivity were carried out for semiconductor structures with a two-dimensional electron gas. Khar’kov State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 91–94, July, 1997.     

Contribution of evanescent waves to the far field: the atomic point of view

Evanescent modes of the electromagnetic field are seldom invoked in conventional far-field optics, as their contribution far from the source (a few wavelengths) is negligible. Contradicting this fact, in recent theoretical works, based on a particular decomposition of the free-space Green tensor, it has been asserted that evanescent waves do indeed contribute to the far field, where they appear as an additional ~1/r component of the field. We provide an explicit demonstration that evanescent modes do not contribute to the power radiated to the far field by any dipolar source. First we derive an expression for the free-space field susceptibility in which contributions from evanescent and homogeneous modes are separated, and then we use linear response theory to compute the decay rate for an atomic dipole in vacuum.     

Additional microwave modes in systems with conductivity of metals and superconductors

Semiclassical model, which takes into consideration the spatial dispersion effects in conductivity and permittivity, demonstrates the possible appearance of additional waves in conducting media, which are known to exist in transparent dielectrics near a narrow absorption band. The dispersion law of additional waves for modelling media (one-dimensional conductance) with parameters of Cu and Nb is obtained, which predicts the novel phenomenon—the possibility for additional microwave modes to propagate in metals with low enough attenuation at cryogenic temperatures.     

Oscillations of a three-component assembly with or without magnetic field

The plasma is taken to be composed of singly ionized molecules, free electrons and neutral molecules, each of the component being described by the hydromagnetic equations, modified to take into account the displacement current, existence of free charge in the medium, and the modified current equation without involving the scalar conductivity. The basic equations are linearized and only small amplitude waves are considered. In the absence of any external magnetic field, the transverse and longitudinal modes of oscillation separate out. In the transverse part a coupled plasma oscillation occurs which could be propagated only above a certain critical frequency and in the longitudinal part one extraordinary mode of propagation occurs having a forbidden range of frequencies. When there is an external applied magnetic field, ordinary and extraordinary waves are propagated along the direction of the magnetic field, whereas only ordinary waves are propagated transverse to the magnetic field. The critical frequencies above which these waves are propagated are evaluated and, the possible explanation of this medium like behaviour could be the implicit assumption of conductivity being not a scalar.     

Propagation of transverse electromagnetic waves with gravitational perturbations in an isotropic universe

The combined behavior of gravitational and electromagnetic perturbations in the radiation-dominated plasma of an isotropic universe is considered. It is shown that transverse electromagnetic waves and vector and tensor gravitational perturbations are independent of one another. The propagation of transverse electromagnetic waves during the lepton and radiation-dominated phases is determined. It is shown that the gravitational perturbations help to excite longitudinal electromagnetic fields in the radiation-dominated plasma.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 49–54, December, 1985.