Anomalous diffusion and thermal diffusion of light ions in a nonisothermal plasma

A turbulent state appearing upon the Cherenkov generation of slow ion acoustic waves by light ions and their induced scattering on heavy ions has been studied. The coefficients of the anomalous diffusion and thermal diffusion of light ions have been determined.     

[Russian Text Ignored]

The plasmon turbulence parametrically excited by two strong external waves with a frequency difference close to twice the electron plasma frequency is investigated in underdense plasmas. The nonlinear stabilization of the growing plasmons due to scattering by ions is described by a nonlinear integro-differential equation for the spectral plasmon energy density. The dependence of the turbulent relaxation of the plasmon energy and its stationary level on the parameters of the plasma and the pump waves is given by analytical and numerical solutions of this equation.     

Excitation of an Additional Region of Short-Wavelength Plasma Oscillations in Ionospheric Heating Experiments

We discuss transfer of plasma waves, excited by a powerful radio wave due to its scattering on artificial ionospheric irregularities, into an additional region of very short plasma oscillations polarized almost perpendicular to the magnetic field. Such a region can exist in the magnetized ionospheric plasma due to the strong spatial dispersion. We take into account the plasma-wave diffusion over the spectrum caused by multiple scattering on irregularities, as well as the nonlinear process of plasma-wave interaction due to induced scattering by ions. The latter process leads to the transfer of primary plasma waves into the additional region. The induced scattering is considered in the differential approximation valid for sufficiently smooth plasma-wave spectra. The numerical calculations are performed for a Maxwellian plasma in which suprathermal electrons are absent. It is shown that in this case, the additional region of plasma waves is excited if the pump frequency is close to but slightly less than the fourth electron gyroharmonic, so that the absorption of primarily excited plasma waves becomes sufficiently strong. Application of our calculations to the results of ionospheric experiments is discussed.     

Decay instability of ion-acoustic wave train (or soliton) and formation of the shock profile

The stability of a periodic ion-acoustic wave of a finite amplitude propagating in a nonisothermal plasma is investigated. It is demonstrated that such a wave is unstable with respect to the splitting into a large number of satellite waves with effective wave numbers different from the wave number of the initial wave. The phase velocity of the satellite waves differs therefore from that of the initial pulse. Hence, the satellite waves with bigger phase velocity will “overtake” the initial pulse and turbulize the upstream plasma. The scattering of ions and electrons by the fluctuations of electric field of turbulent oscillations will cause the energy dissipation of the initial ion-acoustic wave translational motion and produce a collisionless shock wave.     

Electromagnetic Waves in Waveguide Partially Filled with Semiconductor Plasma

The dispersion of electromagnetic waves in waveguides partially filled with semiconductor plasma is investigated for unmagnetized and for strongly magnetized plasma. The effects which may be useful for the plasma electronics are found: In such waveguides there exist a large number of slow waves with typical frequencies ω ≈ ωP/√?_L. The filling at which the different modes at fixed phase velocity are maximum separated in wavelength is found. The thickness of the semiconductor layer at which this effect arises is about hundred micrometers and depends on the crystals' type. In addition to this, in strongly magnetized semiconductor plasma the maximum frequency separation of the typical plasma waves is found at fixed filling. Is it shown that in such systems there exist many surface waves which are of the slow wave type. In the case of strongly magnetized plasma coupling between nonsymmetrical EH- and HE- modes is shown to exist.     

Interaction of a Low Frequency Coherent Magneto-Acoustic Wave with a Turbulent Spectrum of Extra-Ordinary Waves

Starting from nonlinear evolution equations of a three-dimensional extra-ordinary wavepacket in a magnetized plasma and introducing a correlation function, equations are derived that describe interaction of a coherent low-frequency magneto-acoustic wave with a turbulent spectrum of high frequency extra-ordinary waves. These equations are used to derive the dispersion relation for a low frequency magnetoacoustic wave in the presence of a spectrum of turbulent high frequency extra-ordinary waves. In the narrow spectrum case, it is found that a small but finite spread in the spectrum of turbulence has a stabilizing influence on the instability which exists for vanishing spectral width. In the wide spectrum case, the effect of a weak turbulent spectrum of extra-ordinary waves is to produce a slight shift in frequency of the coherent low frequency magneto-acoustic wave and to damp or excite the wave.     

Resonant scattering of ions on charged dust particles

Resonant scattering ("scattering through waves") of ions on dust particles in plasmas is considered in the framework of the kinetic theory which consistently takes into account ion-dust collisions and dust charge fluctuations. Resonance with low frequency dusty plasma modes can enhance the ion-dust scattering cross section and the ion drag force on dust particles.     

Wave motion of incompressible turbulent fluid

Evolution of small disturbances in a fully developed incompressible turbulent flow is considered on the base of the transport equation for the single-point probability density function (PDF) of velocity fluctuations. It is shown that at high frequencies this equation is similar to the Vlasov equation for charged plasma in a self-consistent electromagnetic field having longitudinal wave solutions for turbulent stresses similar to Langmuir waves. It is found that the longitudinal waves of turbulent stresses have a constant phase velocity and can be damped, neutral, or growing waves, depending on the type of undisturbed probability density function of velocity fluctuations. The obtained result differs from the previously published solutions to this problem using the statistical moments closures according to which the wave disturbances should be neutral or damped. The possibilities of experimental observation of longitudinal waves of turbulent stresses are analyzed.     

Distribution of the probability of oscillations of the surface of liquid hydrogen in the turbulent regime

The probability distribution density of the deviation of the surface of liquid hydrogen from the equilibrium plane state in the system of capillary waves has been analyzed. It has been shown that this probability distribution density for the case of the excitation of the surface oscillations by low-frequency noise in the turbulent regime is well reproduced by a Gaussian. When the oscillations are excited by a low-frequency harmonic force, the stochastization of the waves occurs after several scattering events.     

Experimental study of electron-beam interaction with H-type resonator decelerating structure

Electron-beam interaction with an H-type resonator was used to study the anomalous Doppler effect at the electron cyclotron frequency with excitation in an electron beam of slow cyclotron waves, the anomalous Doppler effect at the plasma frequency with excitation of slow plasma waves, the energy relations for slow plasma waves, and the effect of reflected electrons and cyclotron absorption on the development of instabilities.Khar'kov Physicotechnical Institute, Academy of Sciences of Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, Nos. 3, 4, pp. 334–346, March–April, 1992.     

Stimulated Brillouin scattering in a plasma with ion-acoustic turbulence

A theory of stimulated Brillouin scattering (STBS) in a plasma with ion-acoustic turbulence is developed using concepts of parametric instability under conditions when equations of two-temperature hydrodynamics can be used to describe ion-acoustic perturbations of the electron density. The temporal growth rate of the absolute instability and the spatial gain of the scattered wave are determined. The dependence of the threshold density of the radiation flux on the angle between the scattering wave vector and the direction of anisotropy of the turbulent noise is described. A new effect of STBS forbiddenness caused by anomalous turbulent heating of the ions is predicted for a plasma with a high level of turbulent noise.     

Scattering of sound waves by a turbulent wake

In this investigation, the Doppler shifted power spectrum of the scattering cross-section is obtained for plane acoustic waves scattered by fluid flow fluctuations appropriate to a turbulent wake. The wake considered in this paper is assumed almost homogeneous and isotropic and of low Reynolds number.It is shown that the evaluation of the Doppler scattering cross-section essentially reduces to the calculation of the wave number converted and frequency shifted energy spectrum function of the turbulent flow fluctuations. In prescribing the low Reynolds number turbulence spectrum, inertial forces are assumed negligible. Convective effects of the macro-eddies, which cause a Doppler shift in the scattered waves, are considered using a Lagrangian-type of space-time velocity correlation.After finding the spectrum of turbulent fluctuations, the Doppler shifted power spectrum of the scattering cross-section, which characterizes the scattered waves, is obtained explicitly for the far field approximation.     

Nonlinear systems with fast and slow motions. Changes in the probability distribution for fast motions under the influence of slower ones

The influence of slow processes on the probability distribution of fast random processes is investigated. By reviewing four examples we show that such influence is apparently of a universal character and that, in some cases, this universality is of multifractal form. As our examples we consider theoretically stochastic resonance, turbulent jets with acoustic forcing, and two problems studied experimentally by Shnoll on the influence of the Earth’s slow rotation on the probability distribution for the velocities of model Brownian particles and on alpha decay. In the case of stochastic resonance, the slow process is a low frequency, harmonic, external force. In the case of turbulent jets, the slow process is acoustic forcing. In the models based on Shnoll’s experiments, the slow processes are inertial forces arising from the rotation of the Earth, both about its own axis and about the Sun. It is shown that all of these slow processes cause changes in the probability distributions for the velocities of fast processes interacting with them, and that these changes are similar in form.     

Sheath-wave-related resonances in the frequency response of acylindrical monopole in a plasma

Reference is made to a floating or negatively biased antenna immersed in a plasma that is surrounded by an ion sheath. Such an antenna-sheath-plasma system may support slow surface waves at driving frequencies below the electron plasma frequency. Resonances associated with these so-called sheath waves are observed at certain frequencies in the antenna's response to an applied sinusoidal signal. An experimental study of these resonances is presented for a short cylindrical monopole in a low-pressure isotropic argon plasma. The effect on the resonance frequencies of a DC bias applied to the antenna and of plasma density and antenna length was investigated. From the experimental data, the relationship between sheath thickness and antenna potential, and the frequency dependence of the antenna admittance could be derived     

Parametrische Phononen-Turbulenz im Feld zweier zirkular polarisierter UHF-Wellen

The interaction of two strong circulary polarized u.h.f. pump waves with a fully ionized homogeneous plasma is considered. If the difference Ω of their frequencies is near or smaller than twice the ion plasma frequency phonons can be parametrically excited. The threshold value (E₀E₁)_s for this decay-process depends on Ω and the dissipative effects in the plasma. After exceeding the thermal level the phonons are stabilized due to the scattering by the ions. The evolution of the parametrically excited phonon turbulence and the transition into a stationary state are described by a nonlinear integro-differential equation for the spectral energy density of the phonons. This equation is solved analytically as well as numerically and it is shown, that the phonon turbulence is strongly influence by the propagation directions of the pump waves and the ratio of electron- to ion-temperature.     

A theoretical study of hot plasma spheroids in the presence of low-frequency electromagnetic waves

While taking into account thermal motion of electrons, scattering of electromagnetic waves with low frequency from hot plasma spheroids is investigated. In this theoretical research, ions are heavy to respond to electromagnetic fluctuations. The solution of scalar wave equation in spheroidal coordinates for electric potential inside the plasma spheroids are obtained. The variations of resonance frequencies vs. Debye length are studied and consistency between the obtained results in this paper and the results for the well-known plasma objects such as plasma column and spherical plasma have been proved.     

Scattering of light waves by electron electrostatic waves in laser produced plasmas

The propagation of light waves in an underdense plasma is studied using one-dimensional Vlasov-Maxwell numerical simulation.It is found that the light waves can be scattered by electron plasma waves as well as other heavily and weakly damping electron wave modes,corresponding to stimulated Raman and Brilluoin-like scatterings.The stimulated electron acoustic wave scattering is also observed as a high scattering level.High frequency plasma wave scattering is also observed.These electron electrostatic wave modes are due to a non-thermal electron distribution produced by the wave-particle interactions.The collision effects on stimulated electron acoustic wave and the laser intensity effects on the scattering spectra are also investigated.     

On the Nonlinear Processes During Generation of Current Drive

The manifestations of the induced scattering effects in the generation process of current driven by lower-hybrid (LH) waves are studied taking into account the radiative-resonant interactions. The influence extent of the LH wave modulational instability on current drive is estimated. It is shown that the induced scattering of LH waves on plasma particles leads to a change of the LH waves spectrum and through this leads to an essential influence on fast electrons generation rate and the steady-state current drive. The modulational instability of LH waves can provide a “spectral gap” filling in the case of sufficiently strong LH wave pumping.     

Vertical motions in the lower ionosphere and a sporadicE-layer

We propose a calculation technique for the main characteristics of a sporadic E-layer, including the effective recombination coefficient, the relative content of meteor and atmospheric ions in the layer, and the time of its evolution. This technique is based on measurements of vertical plasma velocities by the method of resonance scattering of radio waves by artificial periodic inhomogeneities of the electron density. The contribution of internal gravity waves and turbulent motions to the formation of sporadic layers is estimated. The characteristic values of the turbulent velocity measured by this method at the heights of the turbopause are presented. The possible mechanisms of mid-latitude sporadic E-layer formation at heights of 90 to 120 km are considered. Experimental studies confirmed the main statements of the wind shear theory concerning the determining role of the redistribution of ionization under the action of atmospheric winds with vertical gradient of velocity in the formation of E_s. Deceased. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 1, pp. 26–35, January, 1999.