Whistler Wave Radiation Research Articles

Whistler Wave Radiation From Phased Loop Antennas in a Magnetoplasma

Whistler Wave Radiation From Phased Loop Antennas in a Magnetoplasma

Radiation of Whistler Waves from a Source with a Rotating Near-Zone Magnetic Field in a Magnetoplasma

Radiation of Whistler Waves from a Source with a Rotating Near-Zone Magnetic Field in a Magnetoplasma

Radiation of Whistler Waves From a Source With a Rotating Near Magnetic Field in a Magnetized Plasma

Radiation of Whistler Waves From a Source With a Rotating Near Magnetic Field in a Magnetized Plasma

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.

Excitation of whistler waves below the lower hybrid frequency by a loop antenna located in an enhanced density duct

Whistler wave radiation from a loop antenna located in a cylindrical duct with enhanced plasma density is considered in the case where the wave frequency is less than the lower hybrid frequency. Using the full-wave formulation, the total radiation resistance and the partial radiation resistances corresponding to guided eigenmodes of such a duct and unguided waves radiating to the background magnetoplasma are calculated and analyzed as functions of the plasma and source parameters. The emphasis is placed on the radiation characteristics of the considered source in the presence of an artificial near-antenna duct that can be created during active experiments in the ionosphere. Conditions are revealed under which the total radiation resistance is predominantly determined by the excitation of the eigenmodes of the duct. It is shown that the presence of an enhanced density duct can lead to a notable increase in the radiation resistance of a loop antenna in the discussed frequency range even if the duct is rather narrow and capable of guiding only a single low-order eigenmode. The results obtained can be helpful in understanding the basic features of excitation of the ducted whistlers and planning the related ionospheric and laboratory experiments.

Whistler wave radiation from a pulsed loop antenna located in a cylindrical duct with enhanced plasma density

Pulsed radiation from a loop antenna located in a cylindrical duct with enhanced plasma density is studied. The radiated energy and its distribution over the spatial and frequency spectra of the excited waves are derived and analyzed as functions of the antenna and duct parameters. Numerical results referring to the case where the frequency spectrum of the antenna current is concentrated in the whistler range are reported. It is shown that under ionospheric conditions, the presence of an artificial duct with enhanced density can lead to a significant increase in the energy radiated from a pulsed loop antenna compared with the case where the same source is immersed in the surrounding uniform magnetoplasma. The results obtained can be useful in planning active ionospheric experiments with pulsed electromagnetic sources operated in the presence of artificial field-aligned plasma density irregularities that are capable of guiding whistler waves.

Whistler radiation in plasmas with cylindrical magnetic field irregularities

AbstractThe radiation of whistler waves by linear dipole sources immersed in magnetoplasmas with cylindrical magnetic field inhomogeneities are studied. Two types of irregularities are investigated: magnetic field enhancements and depletions. A theoretical analysis is developed for comparatively weak local perturbations of the ambient magnetic field. Results are provided by numerical calculations performed for physical conditions typical of laboratory experiments involving artificially created magnetic field irregularities. It is shown that plasma regions with locally enhanced (depleted) magnetic field intensities can increase (decrease) the amplitudes of whistler waves radiated by dipole sources, regardless of their orientation with respect to the ambient magnetic field. Results are relevant to space and laboratory experiments on very low-frequency wave radiation.

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.

Quasielectrostatic whistler wave radiation from the hot electron emission of a laser-produced plasma

Measurements are presented of radiated wave electric fields which result from the creation of a dense, laser-produced plasma within a large, uniform background magnetoplasma. The radiated field patterns are consistent for waves propagating along the quasielectrostatic branch of the whistler wave dispersion curve calculated from the background plasma parameters. The energy source of these waves coincides with an observed energetic tail electron population escaping the laser-produced plasma. A prominent feature of the radiated electric fields is a bipolar spike in both time and space, with a cross-field size near that of the initial escaping electron burst and a duration equivalent to one oscillation at the lower hybrid frequency within the background plasma. Additionally, time-windowed snapshots of the whistler wave radiation patterns are shown to provide a remote diagnostic of the cross-field speed of the laser-produced plasma.

Whistler wave emission by a modulated electron beam injected into a plasma column surrounded by a uniform medium

AbstractThe efficiency of whistler wave radiation by a density modulated and thin electron beam of finite length injected parallel with respect to the constant ambient magnetic field into a cylindrical plasma column surrounded by a uniform isotropic medium and aligned along the magnetic field is studied. A rigorous analytical derivation of the wave fields excited by the beam in the plasma column is presented. The time-averaged power radiated by the beam at the modulation frequency is determined. In particular, numerical calculations performed for physical conditions relevant to laboratory magnetized discharge plasmas show that, in the presence of a plasma column, the power lost by the modulated beam can be efficiently enhanced owing to resonant Cherenkov excitation of guided whistler modes at the beam modulation frequency.

Effect of the Relaxation Characteristic Length of Modulated Electron Beam on Whistler Wave Radiation

During the active space experiments of radiating the modulated electron beam,the lin- ear and nonlinear interaction between the electron beam and background plasma may excite whistler wave.Characteristics of the excitation are determined by many factors,including velocity,relaxation characters of electron beam,the frequency of excited waves,and the density of background plasma. The relaxation characteristic length of the modulated electron beam is one of the important factors. In this paper,the influence caused by the exponential attenuation relaxation characteristic length of the modulated electron beam upon the characteristics of the wave excited by the electron beam were studied.Through solving the wave equation when the electron beam is injected into the ho- mogeneous anisotropy space plasma,the solution of the dispersion equation and the Poynting vector representation of the excited wave are obtained.It was shown that the wave radiation intensity excited by the modulated electron beam is enhanced efficiently when the relaxation characteristic length of the electron beam is comparable with the characteristic size of inhomogeneous background plasma.

Laboratory studies of magnetic vortices. I. Directional radiation of whistler waves based on helicity injection

A novel principle for the directional excitation of whistler waves is demonstrated in a laboratory experiment. It is based on helicity conservation of electron magnetohydrodynamic fields in plasmas. Whistler wave packets propagating in opposite directions to a static magnetic field have opposite signs of helicity. Injection of helicity of one sign produces radiation in one direction. This is accomplished with an antenna consisting of a loop linked through a torus. Directionality of 20 dB is readily achieved. The direction of radiation is electronically reversible. Transmission between two antennas is unidirectional, hence nonreciprocal. Possible applications include secure communication, direction finding, and efficient power deposition in radio frequency (rf) heating.

Erratum: “Laboratory studies of magnetic vortices. I. Directional radiation of whistler waves based on helicity injection” [Phys. Plasmas 6, 2989 (1999)

Erratum: “Laboratory studies of magnetic vortices. I. Directional radiation of whistler waves based on helicity injection” [Phys. Plasmas 6, 2989 (1999)

Laboratory studies of magnetic vortices. I. Directional radiation of whistler waves based on helicity injection

A novel principle for the directional excitation of whistler waves is demonstrated in a laboratory experiment. It is based on helicity conservation of electron magnetohydrodynamic fields in plasmas. Whistler wave packets propagating in opposite directions to a static magnetic field have opposite signs of helicity. Injection of helicity of one sign produces radiation in one direction. This is accomplished with an antenna consisting of a loop linked through a torus. Directionality of 20 dB is readily achieved. The direction of radiation is electronically reversible. Transmission between two antennas is unidirectional, hence nonreciprocal. Possible applications include secure communication, direction finding, and efficient power deposition in radio frequency (rf) heating.

Radiation of whistler waves in a magnetized plasma medium in the presence of density ducts

We investigate the influence of density ducts on the radiation of given sources in a magnetoplasma. We obtain the full-wave solution for the problem of radiation from annular electric and magnetic currents in the presence of a plasma column (density duct) oriented along an external magnetic field and surrounded by a uniform background magnetoplasma. Both the discrete part of the spatial spectrum of excited waves and the continuous part of the spectrum are considered. We calculate the total radiated power and partial powers radiated in separate eigenmodes guided by the column. It is established that in the whistler frequency range the presence of a channel with enhanced plasma density can cause a considerable increase in the radiation power of annular sources. We give concrete estimations for the ionospheric conditions and compare these results with the results obtained previously for the case of a uniform magnetoplasma without density ducts.

Radiation of whistler waves in magnetoactive plasma

In this paper the radiation of ring electric and magnetic currents in magnetoactive plasma in whistler frequency range is investigated. Particular attention is concentrated on the problem of variation of the radiated power distribution over the spectrum of excited waves with variation of the radiator parameters. Attention is also given to the radiation pattern structure near the resonance cone and peculiar caustic directions corresponding to the conic refraction and the Storey angle. It is shown that for ring electric current the consideration of the inhomogeneity in its distribution along the ring can be of importance and can lead, in particular, to a large increase of the relative contribution of the quasi‐electrostatic whistler mode waves to the total radiation power. Detailed numerical calculations have been carried out for the conditions close to ionospheric ones.