Magnetoactive Plasma Research Articles

Radiation of whistler-band waves by a spiral electron beam in magnetoactive plasma in the presence of a density duct

Radiation of a modulated electron beam injected at some angle with respect to the axis of a cylindrical density duct embedded into a magnetoactive plasma is investigated. An expression for the mean power lost by the beam at the modulation frequency is derived and analyzed. It is shown that, in the case of the resonance between the beam and one of the weakly leaking waves of the duct with an increased plasma density, the power lost by the beam at the modulation frequency can increase substantially as compared to the case of injection of this beam into a homogeneous background plasma.

Low-frequency wave instabilities in magnetoactive plasma with spatial inhomogeneity of temperature

The dispersion relation (DR) has been considered for low-frequency waves in a hot magnetoactive collisional plasma with 'longitudinal' large-scale electric field E 0 (t) and weak spatial inhomogeneity of temperature. The electric field was assumed to be extremely weak ('subdriecer' field) and the quasi-static time variation of its amplitude allows us to use the 'direct initiation' mechanism to describe the instability development. Taking into account the ion thermal motion has not changed the form of the DR. which has remained the polynomial of the fourth order, hut it has essentially complicated the form of its coefficients. As compared with previous investigations, these changes have resulted in the changes of the solutions of the DR. Two of the roots of the DR have remained of the same type ('kinetic Alfven-like waves), but another two have become quite different and get to the range of slow magneto-acoustic waves. Investigation of these new waves has shown that corresponding instability has clearly expressed threshold character, and the value of this threshold depends essentially on the reduced value of the electric field amplitude E 0 (t) and ratio of electron and ion temperatures.

On the Gradient-Current Mechanism of Formation of the Irregular Structure of the High-Latitude Upper Ionosphere

We consider the gradient-current instability of an inhomogeneous magnetoactive plasma in the approximation of double-fluid magnetohydrodynamics. Unlike the known gradient-drift and current-convective instabilities, the gradient-current instability is related to generation of nonpotential quasistatic electric fields polarized orthogonal to the external magnetic field B0 and excited by eddy currents whose density vector lies in the plane passing through the vectors of the magnetic field B0 and large-scale electron-density gradient. It is shown that in the high-latitude upper ionosphere, in the regions containing large-scale currents flowing in and out of the ionosphere along the magnetic field, the gradient-current instability can lead to the appearance of sheet-like irregularities extended predominantly in the plane passing through the geomagnetic-field and regular plasma-drift velocity vectors.

On the conductivity of a magnetoactive turbulent plasma

The problem of determining the effective conductivity tensor of a magnetoactive turbulent plasma is considered in the approximation of isolated particles. Additional gyrotropic terms are shown to appear in the conductivity tensor in the presence of mean, nonzero magnetic helicity. The dispersion of propagating electromagnetic waves changes, additional modes and additional rotation of the polarization plane appear, and the waves can be amplified. The properties acquired by a plasma with helicity are similar to those observed in chiral and bianisotropic electrodynamic media.

Piecewise linear current density recursive convolution FDTD implementation for anisotropic magnetized plasmas

The piecewise linear current density recursive convolution (PLCDRC) finite-difference time-domain (FDTD) method for isotropic dispersive media greatly improves accuracy over recursive convolution (RC) and current density recursive convolution (CDRC) FDTD approaches but retains its speed and efficiency advantages. This letter extends this approach to anisotropic magnetoactive plasmas which incorporates both anisotropy and frequency dispersion at the same time, enabling the transient solutions of electromagnetic wave propagation in anisotropic magnetoactive plasmas. The high efficiency and accuracy of the method are confirmed by computing the reflection and transmission through a magnetized plasma layer, with the direction of propagation parallel to the direction of the biasing field. A comparison to frequency-domain analytic results and CDRC FDTD results is included.

FDTD Simulation of Electromagnetic Propagation in Magnetized Plasma Using Z Transforms

The electromagnetic propagation through a magnetized plasma slab is studied using the finite-difference time-domain method by means of the z transform The reflection and transmission coefficients of the magnetoactive plasma for the right-hand circularly polarized wave are presented. The comparison of the results of the Z transform and recursive convolution algorithms with analytic values indicates that the Z transform algorithm is more accurate than the recursive convolution algorithm. The Z transform algorithm overcomes the drawback that the recursive algorithm cannot predict the transmission coefficient of the magnetized plasma slab for the right-hand circularly polarized wave in the stop band.

The effect of electromagnetically induced transparency in magnetoactive high-temperature plasmas

We investigate a classical analogue of electromagnetically induced transparency (EIT) currently popular in quantum electronics. We consider EIT for electron cyclotron waves in a finite-temperature plasma. We derive an expression for the effective refractive index of an electromagnetic wave and study the dispersion and absorption of this wave under EIT conditions. Allowance for thermal motion is shown to change radically the behaviour of the dispersion curves for the probe wave in the EIT region compared with the case of a cold plasma. The influence of possible parametric instability on the EIT effect is discussed.

Dispersion relations in relativistic astrophysical outflows

In this work we delineate the physical picture for the propagation of electromagnetic oscillations in a moving plasma. We present calculations devoted to describing the dispersion features of the radiation that propagates within a magnetoactive plasma. Both classical and relativistic treatments have been employed. We have concluded that if the outflow is moving with small velocities, the general motion of the plasma does not affect the propagation of transverse electromagnetic waves. The waves are refracted according to the ordinary refraction law deduced for non-moving magnetoactive plasmas. The global movement does not change the dispersion relations, and the shapes of the corresponding curves remain unaltered. In the relativistic formulation, we have derived the equations that determine the electromagnetic wave spectrum for a moving magnetoactive plasma. In this case, it is found that the flow velocity affects the plasma dispersion properties and is responsible for new dispersion branches: transverse and longitudinal perturbations. The ordinary and extraordinary electromagnetic modes are modified and described by dispersion relations whose points of resonance are also in explicit dependence on the plasma velocity. Furthermore, the relativistic motion causes the split of electromagnetic modes into two independent waves that propagate at different rates. This effect is remarkable for highly relativistic velocities. The results presented in this work may be applied in order to incorporate suitable corrections to the dispersion models, developed to explain the anomalous features of observed lines or continuum radiation, associated with astrophysical relativistic outflows which are present in gamma-ray bursts, blazars, relativistic jets in AGNs (active galactic nuclei), quasars and microquasars.

Effect of magnetic field on the thermal nonlinearity of surface waves in plasma-metal structures

A study is made into the effect of the nonlinear mechanism of plasma electron heating on the dispersion properties of potential surface waves propagating along the interface between a metal and finite-pressure magnetoactive plasma. An external steady magnetic field is directed normally to the interface. Different mechanisms of electron energy loss are treated in a weak heating approximation. The energy balance equation is used to determine the spatial distribution of the plasma electron temperature under conditions of nonlocal heating. The effect of the plasma parameters on the nonlinear shift of the wavenumber and on the spatial damping factor of surface waves is investigated. The results obtained are valid for both semiconductor and gaseous plasmas.

Linear mode conversion in inhomogeneous magnetized plasmas during ionospheric modification by HF radio waves

The propagation of high‐frequency (HF) radio waves in an inhomogeneous magnetoactive plasma and generation of plasma waves at the resonance layer near the reflection layer of the ordinary mode are studied using one‐dimensional (1‐D) and two‐dimensional full‐wave codes. The characteristics of the mode‐conversion process are investigated in linear and parabolic density profiles as the angle of incidence is varied. We present the 1‐D results for the wave propagation relevant to the high‐latitude heater facility at Tromsø and the midlatitude facility at Arecibo. For the facility at Arecibo, the 2‐D wave propagation in a plasma density approximating an overdense sporadic‐E patch is investigated to determine the localized regions of amplified intensity, where plasma waves can facilitate acceleration of fast energetic electrons, resulting in observed enhanced airglow.

Perfectly matched layers for radio wave propagation in inhomogeneous magnetized plasmas

We present 1D and 2D numerical models of the propagation of high-frequency (HF) radio waves in inhomogeneous magnetized plasmas. The simulations allow one to describe the process of linear conversion of HF electromagnetic waves into electrostatic waves. The waves, launched from the lower boundary normally or at a specified angle on a layer of a magnetoactive plasma, can undergo linear conversion of the incident O-mode into a Z-mode at appropriate locations in an inhomogeneous prescribed plasma density. The numerical scheme for solving 2D HF wave propagation equations is described. The model employed the Maxwellian perfectly matched layers (PML) technique for approximating nonreflecting boundary conditions. Our numerical studies demonstrate the effectiveness of the PML technique for transparent boundary conditions for an open-domain problem.

Parametric transformation of the amplitude and frequency of a whistler wave in a magnetoactive plasma

The results of experiments studying the propagation of a high-frequency whistler wave in a magnetized plasma duct in the presence of an intense low-frequency wave also related to the whistler frequency range are reported. Amplitude-frequency modulation of the high-frequency whistler wave trapped in the duct was observed. A deep amplitude modulation of the signal that can lead to its splitting into separate wave packets is observed. It is shown that an increase in the wave propagation path leads to a broadening of the wave frequency spectrum and to a shift of the signal spectrum predominantly toward the red side. The transformation of the frequency of the high-frequency wave is related with the time-dependent perturbation of the external magnetic field by the field of the low-frequency whistler wave (the relative perturbation of the magnetic field δB/B≤5×10−2).

Excitation of upper hybrid cones in magnetoactive plasma

Results are presented from laboratory studies of the radiation transport from a transmitting to a receiving antenna in a cold magnetoactive plasma in the upper hybrid frequency range. In the low-frequency part of this range, sharp maxima of the transmission coefficient are recorded in the resonant directions. In the high-frequency part, a beamed radiation along the external magnetic field is observed. An analysis of the experiments shows that the Q factor of the angular resonances is primarily limited by the phase effects caused by weak spatial dispersion.

Excitation of Surface Waves in Magnetoactive Plasma by a Moving Charged Particle

Excitation of Surface Waves in Magnetoactive Plasma by a Moving Charged Particle

Fundamental and second harmonic amplitudes in a collisional magnetoactive plasma

We present a theoretical investigation of frequency doubling of electromagnetic wave in homogeneous, collisional and magnetized plasma. The coupled nonlinear equations for fundamental ordinary wave and second harmonic extraordinary wave have been solved. The amplitudes of these waves have been calculated for various values of collisional frequency and distance from the plasma boundary.

Electromagnetically induced transparency in high-temperature magnetoactive plasma

We investigate a classical analog of electromagnetically induced transparency (EIT) currently popular in quantum electronics. We consider EIT for electron cyclotron waves in finite-temperature plasma. We derive an expression for the effective refractive index of an electromagnetic wave and study the dispersion and absorption of this wave under EIT conditions. Allowance for thermal motion is shown to radically change the behavior of the dispersion curves for the signal wave in the EIT region compared to the case of cold plasma.

Low-frequency wave instabilities in a plasma with a quasistatic electric field and weak spatial inhomogeneity

A specific type of plasma-wave instability in a hot magnetoactive collisional plasma due to a weak external electric field and weak spatial inhomogeneity is considered for the cases of kinetic Alfvén-like waves. These low-frequency waves with ω [Lt ] Ωi (where Ωi is the ion gyrofrequency) are solutions of the corresponding dispersion relation. The model integral of Bhatnagar, Gross, and Krook is used for the description of collisions. The quasistatic time variation of the electric field amplitude makes it possible to use the ‘direct initiation’ mechanism to describe instability development. An expression for the growth rate is obtained in the framework of linear theory. The instability in question occurs for a certain equation of state of the plasma. For this equation of state, a numerical analysis of the obtained instabilities is performed.

Flare-plasma diagnostics from millisecond pulsations of the solar radio emission

Two solar radio bursts exhibiting narrow-band millisecond pulsations in intensity and polarization are analyzed. There were considerable time delays between the left-and right-circularly polarized components of the radio emission. The observed oscillations of the degree of polarization are due to the different group velocities of the ordinary and extraordinary modes in their propagation from the source to the observer; the frequency dependence of the delay is in excellent agreement with the theoretically calculated group delay in a magnetoactive plasma. It unambiguously follows that the pulsed radio emission is generated near the double upper hybrid frequency by the nonlinear plasma mechanism, since the source emission has a low degree of polarization. In addition to dispersion effects, a Fourier analysis also reveals effects associated with the source inhomogeneity. We detected a frequency drift of pulsations (autodelays) with different signs for different polarization components. This drift suggests that, apart from the dispersion effects, there are also the effects related to inhomogeneity of the radio source. It is shown, in particular, that the upper hybrid modes (generating the radio emission) are unstable in regions with enhanced gradients of the plasma density and/or magnetic field.

Waves and instabilities in dark interstellar molecular clouds containing ferromagnetic dust grains

The propagation characteristics of magnetization waves, as well as the instabilities of sound waves in a self-gravitating dark interstellar molecular cloud containing ferromagnetic dust grains and baryonic gas clouds, have been theoretically investigated by including the dynamics of both ferromagnetic dust grains and baryonic gases. It has been shown that there exist two types of subsonic or supersonic (depending on the field strength of the magnetization) transverse magnetization waves, which can be regarded as counterparts of Alfven waves (for the parallel propagation) and magnetosonic waves (for the perpendicular propagation) in a magnetoactive plasma. It has also been found that, in addition to the usual Jeans instability, the sound waves suffer a new type of instability, which is due to the combined effects of the baryonic gas dynamics and self-gravitational field in both weakly and highly collisional regimes.

Wave Transformation and Scattering on Stationary Charged Particles in a Magnetoactive Plasma. II

The transformation of upper-hybrid, lower-hybrid, and magnetosonic waves on a heavy charged particle lying at the plane boundary of a magnetoactive plasma is considered. The angular distribution of the radiation resulting from wave transformation is investigated. The transformation of a low-frequency magnetosonic wave is suggested as a possible mechanism for pulsar radio emission.