Collisional Magnetized Plasma Research Articles

On ion-dust streaming instability in a collisional magnetized plasma with warm dust

AbstractThis brief communication discusses theoretically a resistive ion-dust streaming instability in a collisional dusty plasma, where the ions and electrons are magnetized, and the dust is unmagnetized. The instability is driven by ions streaming along the magnetic field. The emphasis is on the case where the dust has large thermal speed, and where the ion drift speed is ≲ the ion thermal speed. Application to possible laboratory experimental parameters is considered.

The dynamics of ions entering the magnetized plasma sheath obliquely – collisional and collisionless situations

The characteristics of ions that enter the plasma sheath with an oblique incident angle have been investigated in the presence of an external magnetic field. The ion dynamics in a collisional and collisionless magnetized plasma sheath have been numerically calculated by using a fluid model. Several values for the ion velocity at the sheath edge, orientation and strength of the magnetic field and the ion-neutral collision frequency have been considered. The results show that in a collisionless magnetized plasma sheath, the behaviour of ions that obliquely enter the sheath with some specific velocities at the sheath edge and at some specific orientations and strengths of magnetic field, is more complicated than that of ions with normal entrance angles. For the oblique entrance of ions, the weak magnetic fields cause some fluctuations in ion velocity around its boundary value, i.e. the ion velocity does not accelerate. However, the numerical calculations show that the ion dynamics in a collisional magnetized plasma sheath are the same for both normal and inclined entrance of ions into the sheath.

The Kinetic of Dust with Different Sizes in a Magnetized Collisional Plasma Sheath

The characteristics of dust are investigated in a magnetized plasma sheath with taking into account the gravitational force and collisions between dust and neutral. The model is based on using fluid method and solving the basic equations of fluid method numerically. As the Lorentz, gravitational and collisional forces depend on the dust radius, the numerical calculations are done for different values of dust radius. It enables us to study the effects of dust size on dust dynamics in a magnetized plasma sheath.

Electromagnetic wave propagation through an overdense magnetized collisional plasma layer

The results of investigations into the feasibility of using a magnetic window to propagate electromagnetic waves through a finite-sized overdense plasma slab are described. We theoretically calculate the transmission coefficients for right- and left-handed circularly polarized plane waves through a uniform magnetized plasma slab. Using reasonable estimates for the plasma properties expected to be found in the ionized shock layer surrounding a hypersonic aircraft traveling in the earth’s upper atmosphere (radio blackout conditions), and assuming a 1 GHz carrier frequency for the radio communications channel, we find that the required magnetic field for propagation of right-handed circularly polarized, or whistler, waves is on the order of a few hundred gauss. Transmission coefficients are calculated as a function of sheath thickness and are shown to be quite sensitive to the electron collision frequency. One-dimensional particle-in-cell simulations are shown to be in good agreement with the theory. These simulations also demonstrate that Ohmic heating of the electrons can be considerable. Two- and three-dimensional particle-in-cell simulations using a simplified waveguide and antenna model illustrate the same general transmission behavior as the theory and one-dimensional simulations. In addition, a net focusing effect due to the plasma is also observed in two and three dimensions. These simulations can be extended to design and analyze more realistic waveguide and antenna models.

Ion dynamics in plasma sheath under the effect of E× B and collisional forces

Using the fluid model, we investigated the velocity, kinetic energy and the density distribution of the ions in collisional and collisionless magnetized plasma sheath. Considering an external magnetic field, the ion movement under the effect of magnetic, electric and collisional forces has been analyzed numerically. The nonexistence of fluctuations in ions kinetic energy in collisionless strong magnetized plasma sheath and increasing the ions velocity in depth direction due to the collisions in some positions in the sheath are shown. The fluctuations of ion velocity in weak magnetized plasma sheath are shown too when ions enter the sheath with oblique incident angle.

Collisional effects in magnetized plasma sheath with two species of positive ions

The effects of ion–neutral collision on the characteristics of a magnetized plasma sheath which consists of two species of positive ions are investigated. It is assumed that the ions have different masses. In contrast to our previous work, the effects of ion–neutral collision frequency are added to the magnetized plasma sheath. Using a three-fluid hydrodynamic model and some dimensionless variables, the dimensionless equations are obtained and solved numerically. By taking into account the ion–neutral collision effects on a magnetized three-component plasma sheath, it is shown that apart from the presence of the second ion species, by increasing the collision frequency of two ions with neutrals, the amplitude of fluctuations of ion species density distributions increases and the position of these fluctuations is shifted towards the plasma sheath edge. Also, by increasing the ion–neutral collision frequency these fluctuations turn off faster than those in a collisionless case. It is shown that in the collisional magnetized plasma sheath, the effects of the presence of the heavier ion species on the lighter ion density turn off much faster in comparison with what happens in a collisionless magnetized plasma sheath. Furthermore, it is found that in a collisionless plasma sheath by increasing the density of the heavier ion species, the normalized electrostatic potential decreases while in a collisional plasma sheath the presence of the heavier ion species does not have any considerable effect on the normalized electrostatic potential. In addition, it is shown that when the distance of each ion species from the plasma sheath boundary becomes larger than five times the electron Debye length (x > 5λDe) the fluctuations of the ion species velocities disappear by increasing the ion–neutral collision frequency. Also, it is found that the electron density distribution decreases by increasing the ion–neutral collision frequency.

A model of turbulence in magnetized plasmas: Implications for the dissipation range in the solar wind

This paper studies the turbulent cascade of magnetic energy in weakly collisional magnetized plasmas. A cascade model is presented, based on the assumptions of local nonlinear energy transfer in wave number space, critical balance between linear propagation and nonlinear interaction times, and the applicability of linear dissipation rates for the nonlinearly turbulent plasma. The model follows the nonlinear cascade of energy from the driving scale in the MHD regime, through the transition at the ion Larmor radius into the kinetic Alfvén wave regime, in which the turbulence is dissipated by kinetic processes. The turbulent fluctuations remain at frequencies below the ion cyclotron frequency due to the strong anisotropy of the turbulent fluctuations, k∥ ≪ k⊥ (implied by critical balance). In this limit, the turbulence is optimally described by gyrokinetics; it is shown that the gyrokinetic approximation is well satisfied for typical slow solar wind parameters. Wave phase velocity measurements are consistent with a kinetic Alfvén wave cascade and not the onset of ion cyclotron damping. The conditions under which the gyrokinetic cascade reaches the ion cyclotron frequency are established. Cascade model solutions imply that collisionless damping provides a natural explanation for the observed range of spectral indices in the dissipation range of the solar wind. The dissipation range spectrum is predicted to be an exponential fall off; the power‐law behavior apparent in observations may be an artifact of limited instrumental sensitivity. The cascade model is motivated by a program of gyrokinetic simulations of turbulence and particle heating in the solar wind.

The Features of The Angular Spectrum of Scattered Radiation by Turbulent Collisional Anisotropic Magnetized Plasma

Statistical characteristics of the angular power spectrum of scattered radiation for power law spectrum of electron density ∞uctuations in turbulent collisional anisotropic magnetized plasma are considered. Investigation of phase ∞uctuations of radiowaves in the atmosphere is stimulated by development of interferometric methods of natural and artiflcial objects' observation. Measurements of correlation lengths of refraction coe-cient of the ionosphere using refractometer in both vertical and hori- zontal directions points out to anisotropy of inhomogeneities in the ionosphere. The irregularities have a variety of sizes and usually are elongated along the magnetic fleld direction. It has been found that small ( • 10km) F region irregularities are highly elongated along the direction of the magnetic fleld and large anisotropy could be also expected in case of certain types of plane waves propagating in the ionosphere. On the other hand, large irregularities (‚ 10km) may be only weakly anisotropic. Experimental observation of satellite signals shows that a power-law spectrum of ionospheric irregularities gives a better agreement to the data than Gaussian spectrum. The difierence between the power-law and Gaussian wavenumber spectra is signiflcant, since difierent scintillation spectral shapes give difierent scintillation levels and ∞uctuation rates. Statistical char- acteristics of the spatial spectrum of radiation scattered on anisotropic electron density ∞uctuations for anisotropic Gaussian correlation function have been investigated in (1,2). The present paper reports the results of analysis of the angular power spectrum for power law spectrum of electron density ∞uctuations in the F region of the ionosphere.

Some properties of the angular power distribution of electromagnetic waves multiply scattered in a collisional magnetized turbulent plasma

A study is made of oblique incidence of a small-amplitude plane electromagnetic wave on a semi-infinite slab of a collisional turbulent plasma in an external uniform magnetic field. In the small-angle scattering approximation, the condition for neutralizing the effects of oblique incidence and plasma anisotropy on the statistical properties of radiation multiply scattered in the absorbing plasma medium is determined by using the methods of geometrical optics. The validity of this condition was confirmed by numerical calculations based on the statistical modeling technique. The effect of the shape of the spectrum of the electron density fluctuations on the shape of the angular power distribution of a multiply scattered radiation is investigated.

Origin of ELF/ULF waves triggered by positive cloud to ground lightning above mesoscale connective systems

Powerful electric currents and transient luminous events (sprites, blue jets and gigantic jets) have been detected in discharges between thunderclouds and the lower Ionosphere. The occurrence of such phenomena is strongly related to the occurrence of Ultra Low Frequency (ULF ∼ 6–50 Hz) waves and to the occurrence of positive polarity cloud‐to‐ground flashes. In the present letter, we present a novel mechanism to explain the origin and propagation of the observed ULF waves. Ionospheric clouds are composed of charged ice/smoke particulates, protons, electrons and neutrals. Our objective here is to show that such partially ionized dusty plasmas with streaming electrons in ionospheric clouds may support unstable ULF dust acoustic waves (DAWs). For our purposes, we employ a multifluid dusty plasma model and derive the dispersion relation for modified DAWs in a magnetized collisional plasma. The dispersion relation is analyzed numerically to obtain the growth rate and threshold.

Iondust two-stream instability in a collisional magnetized dusty plasma

The effect of an external magnetic field on an ion-dust two-stream instability in a collisional dusty plasma is investigated. We consider the parameter regime in which the ions and electrons are strongly magnetized, while the charged dust is unmagnetized. The presence of a magnetic field tends to hinder the growth of the instability. The implications for laboratory dusty plasmas such as 'plasma crystals' are discussed.

Drift‐ordered fluid equations for modelling collisional edge plasma

AbstractThe fluid description of collisional magnetized plasma by Braginskii is based on an ordering assuming the species flow velocities to be on the order of the ion thermal speed. This large flow assumption is normally not valid for plasma fusion devices in general and tokamak edge plasmas in particular. To remove this shortcoming Mikhailovskii and Tsypin developed a plasma fluid description assuming the flow velocities to be on the order of the diamagnetic drift velocities, which are smaller than the ion thermal speed. However, when deriving their equations Mikhailovskii and Tsypin missed important terms in their expressions for the species collisional viscous stress tensors. Starting from corrected Mikhailovskii‐Tsypin fluid equations, we derive a system of non‐linear reduced equations describing field‐aligned fluctuations in low‐beta collisional magnetized edge plasma; namely, equations for plasma density, electron and ion energies (or, equivalently, temperatures), parallel ion flow velocity, parallel current, vorticity (or, equivalently, electrostatic potential), perturbed parallel electromagnetic potential, and perturbed magnetic field. Our equations locally conserve particle number and total energy, and insure that perturbed magnetic field and total plasma current are divergence‐free. In addition, while intended primarily for modelling plasma turbulence, they contain the neoclassical results for plasma current, parallel ion flow velocity, and parallel gradients of equilibrium electron and ion temperatures. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhanced Raman scattering of a rippled laser beam in a magnetized collisional plasma

In the laser–plasma interaction experiments, self-focusing and filamentation affect quite a large number of other parametric processes including stimulated scattering processes. Nonlinearity considered in the present problem is the collisional type. The coupling between the main beam, ripple, and excited electron plasma wave is strong. Authors have investigated the growing interaction of a rippled laser beam with an electron plasma wave leading to enhanced Raman scattering. An expression for scattered power is derived and the effect of the externally applied magnetic field on the enhancement of scattered power is observed. From computational results, it is observed that the effect of increased intensity of the main beam leads to suppression of power associated with the Raman scattered wave.

Nonlinear evolution of dust waves driven by cross‐field electron currents

The nonlinear evolution of dust waves generated by a low‐frequency Hall current instability in a magnetized collisional dusty plasma is investigated with theory and nonlinear numerical simulations. This instability is believed to have broad applications to irregularity production in regions where dust is present in the earth's ionosphere such as noctilucent clouds and meteor trails. The instability is driven by an electron current and is an analog, in the dust acoustic type wave regime, of the well‐known Farley‐Buneman instability. The results indicate that the instability nonlinearly saturates with dust heating and the production of secondary waves that propagate in a direction perpendicular to the primary dust acoustic type waves.

Rotation in collisional strongly coupled dusty plasmas in a magnetic field

Recent experiments on strongly coupled plasmas in a magnetic field and a background of neutrals have revealed that the dust component exhibits a rigid rotation of order a fraction of a radian/s. The rotation arises spontaneously and seems to be in the direction of ion rotation (which in turn is determined by a competition between E⃗×B⃗ and diamagnetic rotations of the ions in the collisional magnetized plasma). In this Letter a possible interpretation of these results, based on the use of fluid equations, is offered.

Guided Wave Propagation in Inhomogeneous Collisional Magnetized Plasmas

Previous studies on the influence of transverse plasma-density nonuniformity and collisions on the propagation of electromagnetic surface waves along plasma columns are extended to magnetized-plasma cases of Trivelpiece-Gould modes. The analysis based on numerical results concentrates on situations of moderate axial magnetic field strengths where similarities to unmagnetized cases remain, though modified and reduced with growing magnetic field. Combined effects of collisions, radial plasma-density inhomogeneity and degree of plasma magnetization on the propagation properties of the waves are emphasized. The resonances in the radial field distribution, which occur as long as the wave frequency can match the upper hybrid frequency in the radial density profile are discussed.

Nonlocal theory of drift type waves in a collisional dusty plasma

A nonlocal theory of low-frequency drift-type waves has been developed in a magnetized collisional dusty plasma in a sheared slab geometry. It is shown that the well-known stability of the drift waves in a sheared slab geometry does not hold in the presence of dust particles and a new unstable mode exists for typical laboratory plasma parameters.

Low-Frequency Waves in a Magnetized Collisional Dusty Plasma

A dispersion relation for low-frequency electrostatic waves in a magnetized, homogeneous, and collisional dusty plasma is derived from a set of continuity, momentum, and energy equation, together with Poisson equation. It has been found that there exist three modes: the wholly damped mode due to thermal diffusion, damped dust acoustic wave, and damped dust cyclotron wave. The former two modes were discovered by Wang X.G. et al. [Phys. Plasmas 4, (1997) 3759] for the first time in an unmagnetized dusty plasma; the latter one is reduced to the purely oscillating mode [N.D'Angelo, Planet. Space Sci.38,1143(1990)], when the collision is neglected. The influences of dust grain density, neutral gas pressure, and magnetic field on the waves are discussed. Another possible explanation to PIC (particle in cell)-simulation results carried out by Otain and Bhattacharjee [Phys. Rev. Lett. 78,1468 (1997)] is suggested.

Excitation of current-driven electrostatic ion-cyclotron waves in presence of a transverse direct current electric fields in a magnetized plasma

The temporal evolution of the current-driven electrostatic ion–cyclotron (CDEIC) instability is investigated in the presence of a transverse dc electric field in a collisional magnetized plasma. It was found that the inclusion of a transverse dc electric field in addition to the magnetic field changes the dispersion characteristics of the ion cyclotron waves. The growth rate of the instability increases with the mode frequency and has the largest value at the mode frequencies 43 kHz (for ω≫kzvte) and 7.53 kHz (for kzvti≪ω≪kzvte) when the electron drift velocity is less than the critical value for the CDEIC instability. The growth rate also increases with the guide magnetic field and has the largest value at the magnetic fields 1.0 kG (kyρi∼0.35) for ω≫kzvte and 0.1 kG (kyρi∼0.2) for kzvti≪ω≪kzvte. The growth rate is a sensitive function of electron collision frequency. The results of the theory are applied to explain some of the experimental observations of Koepke et al. [IEEE Trans. Plasma Sci. 20, 631 (1992)].

QUASI-STATIONARY SOLAR WIND IN RAY STRUCTURES OF THE STREAMER BELT

It is shown on the basis of analyzing the LASCO/SOHO data that the main quasi-stationary solar wind (SW), with a typical lifetime of up to 10 days, flows in the rays of the streamer belt. Depending on R, its velocity increases gradually from V≈3 km s−1 at R≈1.3 R⊙ to V≈170 km s−1 at R≈15 R⊙. We have detected and investigated the movement of the leading edge of the main solar wind at the stage when it occupied the ray, i.e., at the formative stage of a quasi-stationary plasma flow in the ray. It is shown that the width of the leading edge of the main SW increases almost linearly with its distance from the Sun. It is further shown that the initial velocity of the inhomogeneities (`blobs') that travel in the streamer belt rays increases with the distance from the Sun at which they originate, and is approximately equal to the velocity of the main solar wind which carries them away. The characteristic width of the leading edge of the `blob' δ≈R⊙, and remains almost unchanging as it moves away from the Sun. Estimates indicate that the main SW in the brightest rays of the streamer belt to within distances at least of order R≈3 R⊙ represents a flow of collisional magnetized plasma along a radial magnetic field.