Homogeneous Magnetoplasma Research Articles

Faraday rotation in nonreciprocal photonic time-crystals

Faraday rotation is one of the most classical ways to realize nonreciprocal photonic devices like optical isolators. Recently, the temporal analog of Faraday rotation, achieved through time-interfaces, was introduced [Li et al., Phys. Rev. Lett. 128, 173901 (2022)]. Here, we extend this concept to the periodic switching regime by introducing nonreciprocal photonic time-crystals (NPTC), formed by switching material properties of a spatially homogeneous magnetoplasma medium periodically in time. Based on a temporal transfer matrix formalism, we study the NPTC band structure and show that temporal Faraday rotation can be achieved in both momentum bands and (partial) bandgaps. When combined with the bandgaps of the NPTCs, the temporal Faraday effect can enable a unidirectional wave amplifier by extracting energy from the modulation. Our study expands the catalog of photonic time-crystals (PTCs), forging a link between photonic nonreciprocity and parametric gain and shedding light on unexplored functionalities of PTCs in wave engineering.

A Multigap Loop Antenna With Phased Excitation in a Magnetoplasma

Electrodynamic characteristics of a multigap loop antenna immersed in a homogeneous magnetoplasma are studied using the integral equation method. The antenna has the form of a perfectly conducting, infinitesimally thin, narrow strip coiled into a ring with its axis parallel to an external static magnetic field. The antenna current is excited by appropriately phased external voltages applied across the gaps of the strip. A closed-form solution for the current distribution of the antenna is obtained, and the elements of its input admittance matrix are found. Based on this solution, conditions are determined under which such an antenna with phased excitation is capable of selectively exciting waves with given azimuthal indices in the surrounding magnetoplasma.

Radiation of twisted whistler waves from a crossed-loop antenna in a magnetoplasma

A study is made of the radiation of whistler waves with helical phase fronts from nonsymmetric sources immersed in a homogeneous cold magnetoplasma. The emphasis is placed on calculating the radiation resistance of an antenna in the form of two orthogonally crossed circular loops with quadrature-phased currents using an approach that is based on an eigenfunction expansion representation of the excited field. Analytical and numerical results are reported for the radiation characteristics of such an antenna in the whistler range and differences in the behavior of the radiation resistance below and above the lower hybrid resonance frequency are revealed. The results obtained can be useful in understanding the basic features of excitation of twisted whistler waves in a magnetoplasma.

Theory of a Circular Loop Antenna Located on the Surface of a Dielectric Column in a Magnetoplasma

We study the electrodynamic characteristics of a circular loop antenna located on the surface of a dielectric column in a homogeneous magnetoplasma. The antenna has the form of an infinitesimally thin, perfectly conducting narrow strip coiled into a ring and is excited by a monochromatic given voltage. Singular integral equations for azimuthal harmonics of the antenna current are obtained in the case where the dielectric column is aligned with an external magnetic field. Based on the solution of these equations, the current distribution and input impedance of the antenna are found and analyzed. It is shown that in the resonant frequency ranges of a magnetoplasma, these characteristics admit a simplified analytical description, which corresponds to the transmission line theory with a complex current-distribution constant.

Formation of solitary structures in uniform and nonuniform magnetoplasmas with superthermal electrons: a non-reductive perturbative approach

Electrostatic solitary structures are studied in uniform and nonuniform magnetoplasmas with superthermal electrons. In the linear analysis, the differences in the acoustic frequencies for Maxwellian, Cairns, and Kappa distributed electrons for both homogeneous and inhomogeneous plasmas are highlighted and discussed. It is shown that using the linear dispersion relation, nonlinear Zakharov-Kuznetsov (ZK) equation can be derived both for the homogeneous and inhomogeneous magnetoplasmas. The solution of the ZK equation is presented using the tangent hyperbolic method. It is found that the increasing magnetic field and the angle of propagation enhances the amplitude whereas the increasing number density mitigates the amplitude of the acoustic drift solitary wave. Furthermore, it is observed that the amplitude of the solitary structure is maximum for Cairns, intermediate for Maxwellian, and minimum for the Kappa distributed electrons. The results presented in this paper may be beneficial to understand the formation of electrostatic drift solitary waves in planetary environments where the nonthermal population of electrons are observed by various satellite missions.

Korteweg-de Vries Burgers equation for magnetosonic wave in plasma

Korteweg-de Vries Burgers (KdVB) equation for magnetosonic wave propagating in the perpendicular direction of the magnetic field is derived for homogeneous electron-ion magneto-plasmas. The dissipation in the system is taken into account through the kinematic viscosity of the ions. The effects of kinematic viscosity of ions, plasma density, and magnetic field strength on the formation of magnetosonic shocks are investigated. It is found that the shock strength is enhanced with the increase in the plasma density of the system. However, the increase in magnetic field strength decreases the amplitude of magnetosonic shock wave. The critical value of the dissipative coefficient to form oscillatory profile and monotonic shock is also discussed. The numerical results have also been plotted by taking the parameters from laboratory plasma experiments.

Shocks, explosions, and vortices in two-dimensional homogeneous quantum magnetoplasma

Using the quantum hydrodynamic model for a uniform quantum magnetoplasma, and considering that the collision between ions and neutrals is dominant, a two-dimensional nonlinear system is derived. The linear dispersion relation is obtained and thus the variations of the dispersion relation with the obliqueness angle and density are discussed in detail. Shock, explosion, and vortex solutions of the nonlinear system are obtained. It is found that increasing the plasma density may enhance the strength of the shock and the width of the explosion. However, the higher the collision frequency is, the weaker the shock and the narrower the explosion will be. The temporal and spatial distributions for the vortex potential are studied. Spatially, it forms a periodic vortex street. Temporally, the vortex street may evolve in various ways owing to the arbitrary function of time.

An alternate approach to study electrostatic solitary waves in homogeneous and inhomogeneous quantum magnetoplasmas

Ion acoustic drift solitary wave is studied in both linear and nonlinear regimes in an electron-ion quantum magnetoplasma. It is shown that using the linear dispersion relation, nonlinear Zakharov–Kuznetsov (ZK) equation can be derived in an inhomogeneous quantum magnetoplasma for ion acoustic drift solitary wave in a certain parametric range. The solution of the ZK equation is also presented using the tangent hyperbolic method. It is found that the quantum Bohm potential (via increasing number density), angle of propagation, and the magnetic field affect the propagation characteristics of the nonlinear quantum ion acoustic drift wave. The results presented in this paper may be beneficial to understand the formation of electrostatic drift solitary waves in dense magnetized plasmas.

Whistler wave radiation from a loop antenna located in a cylindrical density depletion

Electromagnetic radiation from sources in a magnetoplasma containing a radially nonuniform cylindrical density depletion is considered. Using a rigorous solution for the total field comprising both the discrete and continuous parts of the spatial spectrum of excited waves, the radiation resistance of a loop antenna and the efficiency of excitation of different modes by such a source are determined in the whistler range. Based on the numerical results, conditions are revealed under which the power radiated from a loop antenna located in a density depletion is dominated by the contribution of either discrete- or continuous-spectrum modes. It is found that the radiation resistance of the loop antenna in a weakly nonuniform density depletion can be notably greater than that in a homogeneous magnetoplasma whose parameters coincide with those near the depletion axis. The results are relevant to the basic properties of whistler wave excitation in the presence of field-aligned plasma density irregularities and can be useful for wave diagnostics in laboratory and space plasmas.

Kinetic Alfvén waves in a homogeneous dusty magnetoplasma with dust charge fluctuation effects

Kinetic Alfvén waves with finite Larmor radius effects have been examined rigorously in a uniform dusty plasma in the presence of an external/ambient magnetic field. Two-potential theory has been applied for these electromagnetic waves and the dispersion relation is derived which shows a cutoff frequency at the dust-lower-hybrid frequency due to the hybrid motion of magnetized ions and cold and unmagnetized dust dynamics. The dust charge fluctuation effect was analyzed for finding the damping of the electromagnetic kinetic Alfvén waves, which arises on account of the electrostatic parallel component of the waves. The dust charge fluctuation damping is seen to be contributed dominantly by the perpendicular motion of electrons and ions in the dusty magnetoplasma.

Volume and surface longitudinal waves in a cold inhomogeneous magnetoplasma

We study analytically and numerically volume and surface longitudinal waves in a dense weakly magnetized inhomogeneous plasma. First, the well-known results for volume and surface waves in homogeneous and semi-bounded magnetoplasmas are presented for reference. Problems with similar geometry are then studied for plasmas with nonuniform density distributions close to those observed in experiments.

Whistler Wave Emission from a Modulated Electron Beam in a Collisional Magnetoplasma in the Presence of a Density Duct

We study the radiation from a modulated electron beam injected along the axis of a cylindrical density duct in a magnetoplasma. An expression for the average power lost by the beam at the modulation frequency is obtained and analyzed. It is shown that in the case of Cerenkov resonance of the beam with a weakly damped whistler mode of an enhanced-density duct, a noticeable increase in this power is possible compared with the case where the beam is injected in a homogeneous background magnetoplasma. Based on the results of numerical calculations performed for conditions of the Earth's ionosphere, we give estimates of an increase in the power radiated from the beam in the whistler frequency range in the presence of a cylindrical duct with enhanced density.

Contributions to the electromagnetic wave theory of bounded homogeneous anisotropic media.

An electromagnetic wave theory of bounded homogeneous anisotropic media is developed by using the method of angular spectrum expansion. The series and integral representations of the circular cylindrical wave functions and the spherical wave functions of the first, second, third, and fourth kind for homogeneous anisotropic media are obtained. Each coefficient of the Fourier series of a circular cylindrical wave function is a one-dimensional finite range of integration and every coefficient of the spherical-harmonic-function series is a two-dimensional finite range of integration. The addition theorem of wave functions for anisotropic media can be derived from that of wave functions for isotropic media. Weyl's method of deriving the scalar Green's function in isotropic media is generalized to the study of the dyadic Green's function in anisotropic media. The cold homogeneous magnetoplasma is considered as an illustrative example. For a cold homogeneous magnetoplasma, simplified series representations of wave functions and dyadic Green's functions are given. The distributional singular behavior of the dyadic Green's functions in the source region is investigated and taken into account by solving the static problem and the boundary integral equation is derived.

Multi-species kinetic generalization of the Appleton–Hartree dispersion formula

This paper calculates, on a kinetic basis, the dispersion relation and field polarization for waves propagating linearly through a homogeneous magnetoplasma when thermal velocities are far less than the phase velocity. Approximations are brought in only as necessary and their physical significance explained. The result is an improved derivation of the Sen–Wyller generalization of the Appleton–Hartree formula for velocity-dependent collision frequency. Further generalization to several charged species is made, and the dispersion relation is also considered in terms of the angle between the ambient magnetic field and the group (rather than phase) propagation direction. Special case reduction to the Appleton-Hartree formula is confirmed. Complications concerning the limit of weak spatial dispersion are discussed. The analysis is restricted to weakly ionized plasmas in which the charge to neutral particle mass ratios are small, collisions are weak, and the wave vector is predominantly real.

Nonlinear convective cell equations and dipole vortex solutions in homogeneous magnetoplasmas

A new set of coupled nonlinear equations is derived which govern the dynamics of low-frequency electrostatic plasma motion in a magnetic field. The electron inertia, the electron thermal pressure, as well as the field aligned variations are included. The present system of equations admits vortex dipole solutions under a novel scaling n = ▿ 2 ⦜ Φ .

Filamentation instability of a ion cyclotron wave in a collisionless magnetoplasma

In this work we have studied the filamentation instability of a higher-power electromagnetic ion cyclotron wave in a hot, collisionless and homogeneous magnetoplasma. Fluid equations have been employed to find the nonlinear response of electrons and ions. The low-frequency nonlinearity arises through the transverse ponderomotive force on electrons and ions and the high-frequency nonlinearity arises through the nonlinear current densities of electrons and ions. It is noticed that the ion nonlinearity dominates over the electron nonlinearity for pump waves of ion cyclotron range of frequencies. For typical plasma parameters and a considerable power density (∼10 kW cm−2) of the incident wave the growth rate of the filamentation instability is significantly high (∼106 rad s−1).

Ion transport in turbulent flowing space plasmas

We propose a simple set of equations of motion for the fictitious ensemble average particle, with the effects of the turbulence phenomenologically incorporated into a friction tensor. The components of this tensor reflect the perpendicular and parallel coupling to the bulk flow and are estimated from test particle studies in fluctuating homogeneous magnetoplasmas. The approach is extended to moderately inhomogeneous media, and illustrated with the behavior of bow-shocked lithium ions in the magnetosheath for distinct turbulence regimes.

Electromagnetic radiation from a dipole source in a homogeneous magnetoplasma

An electric Hertzian dipole is immersed in a cold homogeneous magnetoplasma and it is required to calculate the electromagnetic field at a moderate or great distance. Known methods of doing this are reviewed and extended. They all, in effect, express the field as an integral representing an angular spectrum of plane waves or of waves with conical wavefronts. The integral is evaluated by the method of steepest descents and extensions of it. Results are then presented of some calculations for various plasmas containing one or more species of positive ion. A study is made of the dependence of the radiated field, and of its Poynting vector, on direction and on frequency, when the source dipole is parallel to the superimposed magnetic field. There are three conditions where signals of large or very large amplitude can occur, namely ( a ) enhancement for directions very close to the direction of the superimposed magnetic field, ( b ) resonance cones, in which the signal is large for directions where the refractive index is very large, and ( c ) Storey cones and reversed Storey cones, which may be thought of as conical caustic surfaces where two rays have moved to coalescence and give constructive interference. These three features occur only in certain limited frequency ranges. The classification of these results is complicated and necessitates discussion of the transition frequencies of the plasma. For a plasma with more than one species of positive ion the phenomenon of crossover occurs, and its effect on the three types of signal enhancement is discussed.

Reciprocity relations between currents and fields in plane-stratified magnetoplasmas

The dyadic Green's function, relating currents and fields in transverse-k space, is determined for a homogeneous magnetoplasma, and then extended to a plane- stratified system by means of the reflexion and transmission matrices of the medium, taking into account multiple reflexions at the source and observation points. A conjugate problem is next considered, in which the propagation eigenvectors have a certain mirror symmetry with respect to those in the original problem and, by relating the scattering matrices in the two cases, a Lorentz-type reciprocity theorem is derived relating currents and fields in the original problem with the mirrored currents and their associated wave fields which characterize the conjugate problem.

Electrostatic waves potential at the plasma and upper-hybrid resonances

The potential created by an infinitesimal alternating dipole in a Maxwellian magnetoplasma is computed numerically at the plasma and upper-hybrid resonance frequencies when the latter extends from one to three times the electron cyclotron frequency. A linear full kinetic theory is used for a homogeneous magnetoplasma for which the forced ion motion and the collisions are neglected. The integral which gives the potential is evaluated by using the least-damping- roots (LDR) approximation, i.e. by neglecting the higher-order roots of the dispersion equation for electrostatic waves. Some characteristic potential patterns of dipoles parallel and perpendicular to the magnetic field are computed and comparisons with analytical results previously published are made. The numerical and analytical patterns are similar only at the plasma frequency when the dipole is parallel to the magnetic field.