Self-induced transparency and electromagnetic pulse compression in a plasma or an electron beam under cyclotron resonance conditions

Based on analogy to the well-known process of the self-induced transparency of an optical pulse propagating through a passive two-level medium we describe similar effects for a microwave pulse interacting with a cold plasma or rectilinear electron beam under cyclotron resonance condition. It is shown that with increasing amplitude and duration of an incident pulse the linear cyclotron absorption is replaced by the self-induced transparency when the pulse propagates without damping. In fact, the initial pulse decomposes to one or several solitons with amplitude and duration defined by its velocity. In a certain parameter range, the single soliton formation is accompanied by significant compression of the initial electromagnetic pulse. We suggest using the effect of self-compression for producing multigigawatt picosecond microwave pulses.     

Theoretical analysis of electron acoustic shock waves in magnetized superthermal plasma with electron beam

We have analysed the small-amplitude non-linear electron acoustic shock waves by taking into account the effects of electron beam in magnetized plasma. Satellite observations in different regions of the Earth's magnetosphere have shown that the electrostatic solitary waves are generally associated with electron or/and ion beams. The nonlinear Korteweg-de-Vries Burgers (KdVB) equation has been derived by considering the basic fluid equations and dissipation effects. The nonlinear coefficient of KdVB equation comes out to be negative. Only dip-shaped potential structures are reported here. For the parameters discussed in this paper, we did not find positive polarity shocks. This could be due to the restrictions on the plasma parameters since we are using the fixed densities of the cold, hot, and beam electrons as observed by the Viking satellite in the auroral region. In this paper, the importance of the cold electron to hot electron temperature in conjunction with the beam speed is pointed out. Increase in beam density, kinematic viscosity, and magnetic field results in increase in the amplitude while the increase in hot electron concentration and superthermality leads to decrease in potential. The numerical analysis is presented for the parameters corresponding to the observation of burst b event by Viking satellite in the dayside auroral zone of the earth's magnetosphere.     

Parametric generation of low-frequency waves by plasma electrons accelerated under electron cyclotron resonance conditions

It has been shown experimentally that the diamagnetic effect appearing when electrons of a magnetized plasma in the antenna near field are accelerated under electron cyclotron resonance conditions can be used to generate low-frequency waves. The amplitude modulation of a signal supplied to the antenna is accompanied by the modulation of the diamagnetic effect and leads to the emission of waves at the modulation frequency to the surrounding plasma. In this process, the extended plasma region containing accelerated electrons serves as a parametric bodiless antenna. The results of the model laboratory experiments make it possible to propose a method for the parametric generation of low-frequency whistler waves in the Earth’s ionosphere by a powerful amplitude-modulated signal supplied to the satellite-borne antenna.     

Quasi-linear relativistic treatment of electron cyclotron fluctuations in a magnetized plasma

Summary The relativistic quasi-linear theory of electron cyclotron fluctuations is developed for a homogeneous plasma. Expressions are given for the absorption and emission coefficients, consistently with the currently employed linear theory. The extension to the inhomogeneousplasma case is considered and shown to allow the analysis of wave propagation, absorption and emission in plasmas of physical interest.

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Riassunto Si sviluppa la teoria quasi lineare relativistica per le fluttuazioni di onde elettroniche di ciclotrone per un plasma omogeneo. Si otteggono inoltre le espressioni dei coefficienti d'assorbimento ed emissione del plasma, consistentemente con la teoria lineare correntemente usata. Si considera infine l'estensione della teoria ad un plasma disomogeneo, applicandola all'analisi quantitativa di propagazione, assorbimento ed emissione di onde di ciclotrone.

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Резюме Для однородной плазмы развивается релятивистская квазилинейная теория электронных циклотронных флуктуаций. Приводятся вйражения для коэффициентов поглощения и испускания, соответствующих повсеместно используемой линейной теории. Рассматривается обобщения и излучения волн в плазме в физическн интересных случаях.

     

Filamentation of a rotating electron beam in a magnetized plasma

Filamentation of a nonrelativistic rotating electron beam in a magnetized plasma is investigated by solving the kinetic equation and finding its dielectric permitivity. The period and the establishment time of the filamentation structure and threshold for instability development are obtained. It will be shown that only when the external magnetic field strength becomes smaller than a characteristic value, filamentation appears.     

Beam instabilities in the collective Cherenkov effect and anomalous Doppler effect in a spatially bounded system near the nontransparency band

Beam instabilities of the type of the collective induced Cherenkov effect and the anomalous Doppler effect, which develop in a longitudinally bounded electrodynamic system near its nontransparency band (i.e., when the electromagnetic wave excited by the beam has zero group velocity), are considered. The dispersion equation is derived, which defines the instability increments taking into account the emission of radiation from the electrodynamic system. The solutions to the dispersion equation are analyzed for various parameters of the electron beam and of the electrodynamic system.     

Excitation of electron cyclotron harmonic waves due to helical electron beams in a plasma

Instabilities of electron cyclotron harmonic waves due to the anisotropy of the velocity distribution of electrons which was produced by the injection of the electron beam perpendicular to the magnetic field have been observed.     

Correlation properties of black-body radiation in the context of the electron cyclotron emission of a magnetized plasma

Summary The quest for the cause of the anomalously large heat transport in magnetically confined thermonuclear plasmas has motivated detailed studies of fluctuations of various plasma parameters and, among others, of the electron temperature fluctuations. For an optically thick plasma the fluctuations of the electron cyclotron emission, ECE, are proportional to the electron temperature fluctuations up to a critical frequency where this ceases to be true. For the ultimate purpose of recovering, by correlation analysis, the actual plasma temperature fluctuations from the fluctuations of the measured radiation at frequencies above the critical, the mutual correlation properties of two ECE beams are analyzed and a criterion is obtained to decide when the thermal radiation fluctuations are uncorrelated and hence ignorable. The author of this paper has agreed to not receive the proofs for correction.     

Time behaviour of electron cyclotron harmonic waves excited by helical electron beams in a plasma

Time behaviour of instabilities of electron cyclotron harmonic waves due to the anisotropy of the velocity distribution of electrons has been investigated. Measured growth rate was compared with the calculated ones.     

Propagation of electron cyclotron waves in a weakly relativistic plasma with steep density and temperature profiles

Summary A detailed analysis is made of the deduction of systems of differential equations describing the propagation of both ordinary and extraordinary waves in the electron cyclotron frequency range in a stratified plasma, perpendicularly to the magnetic field and across the electroncyclotron fundamental resonance layer. The equations are derived under conditions of not too large electron temperature (the so-called weakly relativistic condition) and of very weak nonuniformities of the confining magnetic field. The effects of the nonhomogeneities of the equilibrium plasma density and temperature are carefully examined. It is shown that the propagation equations derived previously in the literature can be extended with only a moderately larger effort in computations to take account also of very strong density and temperature gradients.     

Nonlinear interactions between electromagnetic waves and electron plasma oscillations in quantum plasmas

We consider nonlinear interactions between intense circularly polarized electromagnetic (CPEM) waves and electron plasma oscillations (EPOs) in a dense quantum plasma, taking into account the electron density response in the presence of the relativistic ponderomotive force and mass increase in the CPEM wave fields. The dynamics of the CPEM waves and EPOs is governed by the two coupled nonlinear Schr?dinger equations and Poisson's equation. The nonlinear equations admit the modulational instability of an intense CPEM pump wave against EPOs, leading to the formation and trapping of localized CPEM wave pipes in the electron density hole that is associated with a positive potential distribution in our dense plasma. The relevance of our investigation to the next generation intense laser-solid density plasma interaction experiments is discussed.     

Enhancement of electron density in the interaction of high-power electromagnetic waves with inhomogeneous magnetized plasma

Propagation characteristics of a high-power electromagnetic wave through an inhomogeneous magnetized plasma is investigated. Considering the momentum transfer equations for electrons and ions and taking into account the ponderomotive force, the distribution of electron density and dielectric permittivity are obtained. Using non-linear dielectric permittivity and Maxwell's equations in the absence of external current and charge densities, non-linear wave equations are achieved. The results indicate that the external static magnetic field can modify the profiles of both the electric and magnetic fields. It is also shown that the external static magnetic field enhances the amplitude of the electron density and the non-linear dielectric permittivity.     

Effect of positron density and temperature on the electron acoustic waves in a magnetized dissipative plasma

Zakharov–Kuznetsov–Burgers (ZKB) equation is derived for electron acoustic shock waves in magnetized e–p–i plasma. In the present model, magnetized plasma containing two electron population with kappa distributed positrons has been considered. The propagation characteristics of three dimensional electron acoustic (EA) shock waves have been studied under the influence of magnetic field. Our present plasma model supports the negative potential shocks. Combined action of dissipation (η), superthermality (κ), concentration of positrons (β), temperature ratio of cold electrons to positrons (σ), and magnetic field (ω_c) significantly modify the properties of EA shock waves. The width and amplitude of the shock structures are modified by various physical parameters. It is found that shock wave width decreases with increase in β, η₀, and ω_c whereas it becomes wider for κ and σ. Further, potential of the shock wave decreases as one departs away from superthermal distribution.     

On the theory of Langmuir waves in a quantum plasma

Nonlinear quantum-mechanical equations are derived for Langmuir waves in an isotropic electron collisionless plasma. A general analysis of dispersion relations is carried out for complex spectra of Langmuir waves and van Kampen waves in a quantum plasma with an arbitrary electron momentum distribution. Quantum nonlinear collisionless Landau damping in Maxwellian and degenerate plasmas is studied. It is shown that collisionless damping of Langmuir waves (including zero sound) occurs in collisionless plasmas due to quantum correction in the Cherenkov absorption condition, which is a purely quantum effect. Solutions to the quantum dispersion equation are obtained for a degenerate plasma.     

Absolute and convective instabilities of electrostatic ion cyclotron waves excited in an ion beam-plasma system

Experimental results are presented for the observation of the absolute and convective instabilities of the electrostatic ion cyclotron waves excited in an ion beam-plasma system.