Whistler detrapping from a density crest duct

A theory of whistler wave leakage from a magnetic field aligned duct with enhanced plasma density is presented. The energy flux from the duct and the corresponding wave attenuation rate are calculated in the WKB approximation. Possible experimental confirmations of the theory are indicated.     

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).     

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. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 9, pp. 730–742, September 2005.     

Cyclotron Wave-Particle Interactions in the Whistler-Mode Waveguide

We study the cyclotron interaction of energetic electrons and whistler waves in plasma waveguides formed by inhomogeneous distribution of cold plasma. Such waveguides can be formed in the Earth's magnetosphere, e.g., by the plasmapause or by ducts with enhanced background-plasma density. In this paper, we consider a cylindrically symmetric model of a magnetospheric duct with enhanced cold-plasma density in a homogeneous magnetic field. The spatial structure of the eigenmodes of such a waveguide is found. We obtain a set of self-consistent quasilinear equations for cyclotron instability with eigenmode structure taken into account, thus generalizing the quasilinear theory of a magnetospheric cyclotron maser.     

Dispersion properties and field structures of eigenmodes of nonuniform plasma waveguides in a longitudinal magnetic field

We study the field structure and dispersion properties of a hybrid eigenmode guided by a nonuniform magnetized plasma waveguide. It is shown that the rotational and quasi-potential waves contribute to the formation of such a mode in the whistler frequency range. Depending on the plasma density, the rotational component of the hybrid mode is determined by either waves with complex transverse wave numbers or whistler waves, or by true surface waves. In the presence of an axial nonuniformity of the plasma in a channel, the transverse field structure of the propagating mode changes, which is stipulated by changes in both the values of transverse wave numbers and their dependence on the radial coordinate. It is found that the spectrum of axial wave numbers of eigenmodes of a plasma waveguide undergoes a pronounced condensation when smoothing the waveguide walls. The damping of the hybrid mode of a nonuniform waveguide due to electron collisions is found and it is shown that collisional losses determine the damping of waves trapped in the waveguide in the experiments on ionization self-channeling of whistler waves. We have found the effect of “displacing” the strong field from the inner core to the background outer region of the waveguide with increasing plasma density on its axis and broadening background region. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 7, pp. 607–617, July 2006.     

Whistler waves guided by ducts with enhanced density in a collisional magnetoplasma

We study the guided propagation of whistler waves along cylindrical ducts with enhanced density in a collisional magnetoplasma. It is shown that under certain conditions, the presence of comparatively small dissipative losses due to electron collisions in a plasma medium can lead to significant changes in the dispersion characteristics and field structures of whistler modes guided by such ducts compared with the case of a collisionless plasma. We present the results of numerical calculations showing such changes in the properties of whistler modes. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 1, pp. 31–49, January 2008.     

Self channeling of whistler waves

Channels of excess plasma density aligned along the magnetic field guide whistler without spatial divergence. If the whistler wave is of sufficient intensity it maintains the channel through its own radiation pressure which pushes the plasma towards regions of increasing wave amplitude.     

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.Nizhnii Novgorod University. Tranlated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 7, pp. 887–908, July, 1994.     

Ionization self-channeling of whistler waves in a collisional magnetized plasma

An investigation is made of the self-interaction of whistler waves (whistlers) involving the formation of waveguide channels in a collisional magnetoactive plasma as a result of its additional ionization by the field of the propagating wave. Simplified equations are derived to describe the behavior of the whistler field in a channel of enhanced plasma density in the presence of electron collisions. Self-consistent distributions of the field and the plasma corresponding to steady-state ionization self-channeling of whistlers are obtained by numerically solving the equations for the field together with balance equations for the electron density and energy. Our estimates indicate that this effect can be observed under laboratory conditions. Zh. éksp. Teor. Fiz. 112, 1285–1298 (October 1997)     

Excitation of chorus-like waves by temperature anisotropy in dipole research experiment (DREX): A numerical study

Due to their significant roles in the radiation belts dynamics, chorus waves are widely investigated in observations,experiments, and simulations. In this paper, numerical studies for the generation of chorus-like waves in a launching device,dipole research experiment(DREX), are carried out by a hybrid code. The DREX plasma is generated by electron cyclotron resonance(ECR), which leads to an intrinsic temperature anisotropy of energetic electrons. Thus the whistler instability can be excited in the device. We then investigate the effects of three parameters, i.e., the cold plasma density nc, the hot plasma density nh, and the parallel thermal velocity of energetic electrons, on the generation of chorus-like waves under the DREX design parameters. It is obtained that a larger temperature anisotropy is needed to excite chorus-like waves with a high nc with other parameters fixed. Then we fix the plasma density and parallel thermal velocity, while varying the hot plasma density. It is found that with the increase of nh, the spectrum of the generated waves changes from no chorus elements, to that with several chorus elements, and then further to broad-band hiss-like waves. Besides, different structures of choruslike waves, such as rising-tone and/or falling-tone structures, can be generated at different parallel thermal velocities in the DREX parameter range.     

Influence of nonlinear effects on whistler emission in magnetoactive plasma

The influence of thermal and strictional nonlinear effects on the whistler emission in magnetoactive plasma is studied experimentally. It is established that a nonlocal thermal nonlinearity determines the directional pattern of the antenna, while a strictional nonlinearity, which is strongest near the antenna surface, is responsible for the matching of the emitter with the surrounding plasma. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 548–551 (25 April 1998)     

Nonsymmetric Whistler Waves Guided by Cylindrical Ducts with Enhanced Plasma Density

We study the guided propagation of whistler waves whose fields depend on the azimuthal angle in cylindrical plasma-waveguide channels (density ducts) aligned with an external magnetic field and surrounded by a uniform magnetoplasma. The main attention is paid to ducts with enhanced plasma density. It is shown that, under certain conditions, such ducts are capable of guiding proper (eigen) modes and improper leaky modes. We present the results of analysis of the dispersion properties and field structures of nonsymmetric modes guided by cylindrical ducts in the whistler frequency range.     

Whistler modes with wave magnetic fields exceeding the ambient field

Whistler-mode wave packets with fields exceeding the ambient dc magnetic field have been excited in a large, high electron-beta plasma. The waves are induced with a loop antenna with dipole moment either along or opposite to the dc field. In the latter case the excited wave packets have the topology of a spheromak but are propagating in the whistler mode along and opposite to the dc magnetic field. Field-reversed configurations with net zero helicity have also been produced. The electron magnetohydrodynamics fields are force free, have wave energy density exceeding the particle energy density, and propagate stably at subelectron thermal velocities through a nearly uniform stationary ion density background.     

Generation of whistler mode in a relativistic plasma

This paper contains the plasma maser interaction between high frequency nonresonant whistler R-mode and low frequency resonant ion acoustic mode in a relativistic plasma. It shows that the whistler R-mode grows through the plasma maser interaction between the relativistic electrons and the ion acoustic fluctuation.      

Density fluctuation spectrum in whistler turbulence

We develop a nonlinear two-dimensional fluid model of whistler turbulence that includes effect of electron fluid density perturbations. The latter is coupled nonlinearly with wave magnetic field. This coupling leads essentially to finite compressibility effects in whistler turbulence model. We find from our simulations that despite strong compressibility effects, the density fluctuations follow the evolution of the wave magnetic field fluctuations. In a characteristic regime where large scale whistlers are predominant, the coupled density fluctuations are found to follow a Kolmogorov-like phenomenology in the inertial range turbulence. Consequently, the turbulent energy is dominated by the large scale (compared to electron inertial length) eddies and it follows a Kolmogorov-like k−7/3 spectrum, where k is a characteristic wavenumber.     

Thermal effects on parallel resonance energy of whistler mode wave

In this short communication, we have evaluated the effect of thermal velocity of the plasma particles on the energy of resonantly interacting energetic electrons with the propagating whistler mode waves as a function of wave frequency and L-value for the normal and disturbed magnetospheric conditions. During the disturbed conditions when the magnetosphere is depleted in electron density, the resonance energy of the electron enhances by an order of magnitude at higher latitudes, whereas the effect is small at low latitudes. An attempt is made to explain the enhanced wave activity observed during magnetic storm periods.     

Plasma Maser Theory of Whistler Waves in the Presence of Ion Cyclotron Turbulence

In this paper we consider the plasma maser theory of whistler waves in the presence of ion cyclotron waves in a magnetized plasma. In a plasma with low frequency ion cyclotron turbulence and a high frequency test whistler wave, growth of the whistler wave takes place because of the turbulent bremsstrahlung interaction between the resonant electrons and the modulated electric fields. The growth rate of the whistler wave is calculated and the results discussed.     

Plasma-aided radiation guiding in a free-electron laser

The introduction of a plasma in a free-electron laser (FEL) helps radiation guiding via nonlinear refraction. At high-radiation power density, when oscillatory electron velocity is comparable to the electron thermal velocity, the radiation pushes plasma radially out, forming a depleted plasma duct and guiding the radiation. The radius of the self-trapped laser is ~c/ω_po, where ω_po is the unperturbed plasma frequency and c is the velocity of light in vacuum     

Electron-Cyclotron Resonance Heating in Tandem Mirrors

Using numerical ray-tracing techniques, we study the propagation and absorption profiles of electromagnetic waves launched in the end cells of three different tandem mirrots: Phaedrus, an overdense low-temperature tandem mirror with plugs; TASKA, a conceptual tandem mirror with plugs and thermal barrier; and TMX-U, a tandem mirror with a significant hot-electron population. In particular, the effects of weakly relativistic thermal anisotropy on the absorption profile are examined. In general, at sufficiently low densities and temperatures, the X mode can access the plasma and achieve significant heating of the electrons. As the electron temperature increases, the X mode gets quickly absorbed at the edge and only the O mode achieves significant penetration and heating. For sufflciently large launching angles, the presence of thermal anisotropy can actually shift the region of maximum absorption towards the electron-cyclotron resonance layer. Regions of whistler instability appear along rays launched nearly along the machine axis, when the thermal-anisotropy ratio, temperature, and density reach sufficiently high values.     

Whistler instability in an electron-magnetohydrodynamic spheromak

A three-dimensional magnetic vortex, propagating in the whistler mode, has been produced in a laboratory plasma. Its magnetic energy is converted into electron kinetic energy. Non-Maxwellian electron distributions are formed which give rise to kinetic whistler instabilities. The propagating vortex radiates whistler modes along the ambient magnetic field. A new instability mechanism is proposed.