Jeans stability of dusty space plasmas

The Jeans stability of dusty plasmas is re-considered. In contrast to a gas, a dusty plasma can support a plethora of wave modes each potentially able to impart to the dust particles the randomising energy necessary to avoid Jeans collapse on some length scale. Consequently, the analysis of the stability to Jeans collapse is many-fold more complex in a dusty plasma than it is for a charge-neutral gas. After recalling some of the fundamental ideas related to the ordinary Jeans instability in neutral gases, we extend the discussion to plasmas containing charged dust grains. Besides the usual Jeans criterion based upon thermal agitation, we consider two other ways of countering the gravitational collapse: (i) via the excitation of dust-acoustic modes and (ii) via a novel Alfvén-Jeans instability, where perturbations of the dust mass-loaded magnetic field counter the effects of self-gravitation. These two mechanisms yield different minimum threshold length scales for the onset of instability/condensation. It is pointed out that for the study of the Jeans instability produced by density enhancements induced in the plasma by the presence of normal wave modes, even more prohibitive plasma size constraints must necessarily be satisfied.     

Ion-acoustic waves in a dust-contaminated plasma

A self-consistent theory of ion-acoustic waves in dusty gas discharge plasmas is presented. The plasma is contaminated by fine dust particles with variable charge. The stationary state of the plasma and the dispersion and damping characteristics of the waves are investigated accounting for ionization, recombination, dust charge relaxation, and dissipation due to electron and ion elastic collisions with neutrals and dusts, as well as charging collisions with the dusts.     

Screening and attraction of dust particles in plasmas

The potential around a dust particle in a plasma is found using the collisional hydrodynamic equations of dusty plasmas, taking into account ion-dust and ion-neutral collisions and considering the plasma source proportional to the dust density. The linear screening is strongly influenced by the collisions and can substantially differ from Debye screening. Attraction of negatively charged dust particles can occur due to overscreening by the ion fluxes in the presence of friction forces.     

Dust acoustic waves in collisional uniform dense magnetoplasma

In order to study the characteristics of dust acoustic waves in a uniform dense dusty magnetoplasma system, a nonlinear dynamical equation is deduced using the quantum hydrodynamic model to account for dust–neutral collisions. The linear dispersion relation indicates that the scale lengths of the system are revised by the quantum parameter, and that the wave motion decays gradually leading the system to a stable state eventually. The variations of the dispersion frequency with the dust concentration, collision frequency, and magnetic field strength are discussed. For the coherent nonlinear dust acoustic waves, new analytic solutions are obtained, and it is found that big shock waves and wide explosive waves may be easily produced in the background of high dusty density, strong magnetic field, and weak collision. The relevance of the obtained results is referred to dense dusty astrophysical circumstances.     

Streaming instability of dust-acoustic mode with helical wavefronts

Making use of the kinetic approach for plasma species, the electrostatic twisted dust-acoustic (DA) waves are studied in a collisionless unmagnetized multi-component dusty plasma consisting of electrons, singly ionized positive ions and charged massive dust grains. The Vlasov-Poisson equations are coupled together to obtain a generalized response function by using the Laguerre-Gaussian (LG) perturbed electrostatic potential and distribution function in the paraxial limit. The dispersive properties and growth rate instability of twisted DA waves are examined with distinct OAM states in a multi-component dusty plasma. Various significant modifications associated with the real wave frequency and growth rate are shown with respect to twist parameter and dust concentration. It is examined that dust concentration enhances the growth rate of twisted DA waves, whereas an increase in twist parameter reduces the growth rate instability. The excitation of twisted DA mode is also found to enhance with streaming speed of inertialess electrons. Our results may be useful for particle transport and trapping phenomena due to wave excitation in laboratory dusty plasmas.     

Theory of dust voids in plasmas

Dusty plasmas in a gas discharge often feature a stable void, i.e., a dust-free region inside the dust cloud. This occurs under conditions relevant to both plasma processing discharges and plasma crystal experiments. The void results from a balance of the electrostatic and ion drag forces on a dust particle. The ion drag force is driven by a flow of ions outward from an ionization source and toward the surrounding dust cloud, which has a negative space charge. In equilibrium the force balance for dust particles requires that the boundary with the dust cloud be sharp, provided that the particles are cold and monodispersive. Numerical solutions of the one-dimensional nonlinear fluid equations are carried out including dust charging and dust-neutral collisions, but not ion-neutral collisions. The regions of parameter space that allow stable void equilibria are identified. There is a minimum ionization rate that can sustain a void. Spatial profiles of plasma parameters in the void are reported. In the absence of ion-neutral collisions, the ion flow enters the dust cloud's edge at Mach number M=1. Phase diagrams for expanding or contracting voids reveal a stationary point corresponding to a single stable equilibrium void size, provided the ionization rate is constant. Large voids contract and small voids expand until they attain this stationary void size. On the other hand, if the ionization rate is not constant, the void size can oscillate. Results are compared to recent laboratory and microgravity experiments.     

Obliquely propagating dust-acoustic solitary waves in magnetized dusty plasmas with two-temperature Maxwellian ions

The nonlinear propagation of dust-acoustic waves in an obliquely propagating magnetized dusty plasma, containing Maxwellian distributed ions of distinct temperatures (namely lower and higher temperature Maxwellian ions), negatively charged mobile dust grains, and Maxwellian electrons, is rigorously investigated and analyzed by deriving the Zakharov-Kuznetsov equation. It is investigated that the characteristics of the dustacoustic solitary waves are significantly modified by the external magnetic field, relative ion and electron temperature-ratio, and respective number densities of two population of ions. The implications of the results obtained from this analysis in space and laboratory dusty plasmas are briefly discussed.     

Instabilities in Yukawa Liquids

A strongly coupled Yukawa liquid is a system of charged particles which interact via a screened Coulomb interaction and in which the electrostatic energy between neighboring particles is larger than their thermal energy but not large enough for crystallization. Various plasma systems including ultracold neutral plasmas and complex (dusty) plasmas can exist in this strongly coupled liquid phase.Here we investigate instabilities driven by the relative streaming of plasma components in three‐dimensional Yukawa liquids with a focus on complex plasmas. This includes a dust acoustic instability driven by weakly coupled ions streaming through the dust liquid, and a dust‐dust instability driven by the counter‐streaming of strongly coupled dust grains. Compared to the Vlasov behavior we find there can be a substantial modification of the unstable wavenumber spectrum due to strong coupling effects (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Small amplitude dust-acoustic soliton energy in dusty plasmas with suprathermal polarization force

The effect of suprathermal polarization force on both linear and weakly nonlinear dust-acoustic solitary structures in a three-component dusty plasma is investigated. For this purpose, a new expression of the polarization force acting on dust particles that include the electronic suprathermal effect is derived. The results are applied to two different experimental dusty plasmas. We have found that the polarization force acting on the dust grains decreases as the electron suprathermality becomes more significant. In addition, we have shown that, for a given value of the spectral index κ , the polarization force magnitude fluctuates from one plasma to another. The changes arising in the propagation of small-amplitude dust-acoustic (DA) solitons due to the presence of this suprathermal polarization force are also analysed. Interestingly, an increase in the magnitude of the polarization force leads to an increase in the amplitude and width of DA soliton and provides more energy to the motion of this soliton.     

��ײ�Գ������������ʲ��г�������Ӱ��

The fluid dynamics model was used to study the influence of the existence of the collisions on the dust particles in a dusty plasma sheath. The main collisions in this study consist of the ionization collision, the collision between electron and neutral particle, the collision between ion and neutral particle, the collision between electron and dust particle, the collision between ion and dust particle. Numerical calculation results are obtained by the fourth-order-Rung-Kutta method. It is shown that both the dust particles’ density and corresponding electricity quantity increase as the following collisions’ frequency enhances, such as ionization collision, the collision between electron and neutral particle, the collision between ion and neutral particle. The charge reduces due to the collisions concluding electron-dust particle and ion-dust particle. In addition, the effect produced by ions’ collision is much more obviously compared with electrons’ collision.     

Sheared Flow Driven Drift Instability and Vortices in Dusty Plasmas with Opposite Polarity

Low-frequency electrostatic drift waves are studied in an inhomogeneous dust magnetoplasma containing dust with components of opposite polarity. The drift waves are driven by the magnetic-field-aligned (parallel) sheared flows in the presence of electrons and ions. Due to sheared flow in the linear regime, the electrostatic dust drift waves become unstable. The conditions of mode instability, with the effects of dust streaming and opposite polarity, are studied. These are excited modes which gain large amplitudes and exhibit interactions among themselves. The interaction is governed by the Hasegawa-Mima (HM) nonlinear equation with vector nonlinearity. The stationary solutions of the HM equation in the form of a vortex chain and a dipolar vortex, including effects of dust polarity and electron (ion) temperatures, are studied. The relevance of the present work to space and laboratory four component dusty plasmas is noted.     

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.     

碰撞对尘埃等离子体鞘层中尘埃颗粒影响

在一维平板鞘层中应用流体模型研究了尘埃等离子体鞘层中碰撞对尘埃颗粒密度和带电量的影响。 研究所涉及的碰撞主要有电离碰撞,电子、离子分别与中性粒子的碰撞,以及电子、离子分别与尘埃颗粒的碰撞。通过采用四阶龙格库塔法,得到了数值解。结果表明,随着电离碰撞或者电子、离子分别与中性粒子碰撞的频率 增加,都将导致鞘层中尘埃颗粒的数密度增大,数密度的极值位置向鞘边位置靠近,尘埃颗粒带电量增多。电子、离子与尘埃颗粒的碰撞,使得尘埃带电量减小。此外,从研究的结果来看,由离子产生的碰撞要比电子产生的碰 撞对尘埃颗粒的影响明显得多。     

Effects of dust size distribution on nonlinear waves in a dusty plasma

For two-dimensional unmagnetized dusty plasmas with many different dust grain species, a Kadomtsev--Petviashvili (KP) equation, a modified KP (mKP) equation and a coupled KP(cKP) equation for small, but finite amplitude dust-acoustic solitary waves are obtained for different physical conditions respectively. The influence of an arbitrary dust size distribution described by a polynomial expressed function on the properties of dust-acoustic solitary waves is investigated numerically. How dust size distribution affects the sign and the magnitude of nonlinear coefficient A(D) of KP (mKP) equation is also discussed in detail. It is noted that whether a compressive or a rarefactive solitary wave exists depends on the dust size distribution in some dusty plasmas.     

Modulated Dust-Acoustic Wave Packets in an Opposite Polarity Dusty Plasma System

The nonlinear propagation of the dust-acoustic bright and dark envelope solitons in an opposite polarity dusty plasma(OPDP) system(composed of non-extensive q-distributed electrons, iso-thermal ions, and positively as well as negatively charged warm dust) has been theoretically investigated. The reductive perturbation method(which is valid for a small, but finite amplitude limit) is employed to derive the nonlinear Schr¨odinger equation. Two types of modes, namely, fast and slow dust-acoustic(DA) modes, have been observed. The conditions for the modulational instability(MI) and its growth rate in the unstable regime of the DA waves are significantly modified by the effects of non-extensive electrons, dust mass, and temperatures of different plasma species, etc. The implications of the obtained results from our current investigation in space and laboratory OPDP medium are briefly discussed.     

Dust-acoustic solitary waves in an adiabatic hot dusty plasma

An adiabatic hot dusty plasma (containing non-inertial adiabatic electron and ion fluids, and negatively charged inertial adiabatic dust fluid) is considered. The basic properties of arbitrary amplitude dust-acoustic (DA) solitary waves, which exist in such an adiabatic hot dusty plasma, are explicitly examined by the pseudo-potential approach. To compare the basic properties (critical Mach number, amplitude and width) of the DA solitary waves observed in a dusty plasma containing adiabatic electron, ion and dust fluids with those observed in a dusty plasma containing isothermal electron and ion fluids and adiabatic dust fluid, it has been found that the adiabatic effect of inertia-less electron and ion fluids has significantly modified the basic properties of the DA solitary waves, and that on the basic properties of the DA solitary waves, the adiabatic effect of electron and ion fluids is much more significant than that of the dust fluid.     

Nonlinear development of the dust acoustic instability in acollisional dusty plasma

We study the nonlinear behavior of the low-frequency dust acoustic instability in a collisional dusty plasma by means of particle simulations. The instability arises due to the streaming of plasma ions and neutrals relative to charged dust grains. According to linear theory, the presence of collisions between the plasma ions and a neutral gas background reduces the growth rate of the instability. Nonlinearly, however, the presence of drifting neutrals maintains the initial relative drift between plasma and dust ions until the unstable waves grow to large amplitude and collisions due to wave-particle interactions exceed the neutral collisions. As a result, stronger nonlinear effects, as manifested by enhanced fluctuations, larger amounts of plasma and dust heating, and a temporary reduction of the relative drift velocity, can occur in the presence of collisions     

Electrostatic dust-acoustic envelope solitons in an electron-depleted plasma

A standard nonlinear Schrödinger equation has been established by using the reductive perturbation method to investigate the propagation of electrostatic dust-acoustic waves, and their modulational instability as well as the formation of localized electrostatic envelope solitons in an electron-depleted unmagnetized dusty plasma system comprising opposite polarity dust grains and super-thermal positive ions. The relevant physical plasma parameters (viz., charge, mass, number density of positive and negative dust grains, and super-thermality of the positive ions, etc.) have rigorous impact to recognize the stability conditions of dust-acoustic waves. The present study is useful for understanding the mechanism of the formation of dust-acoustic envelope solitons associated with dust-acoustic waves in the laboratory and space environments.     

Effects of Vortex-Like Ion Distribution on Dust-Acoustic Solitary Waves in a Self-Gravitating Opposite Polarity Dusty Plasmas

A self-gravitating opposite polarity dust plasma (SGOPDP) medium (containing both positively and negatively charged dust, vortex-like distributed ions and Maxwellian electrons) has been considered in order to examine the effect of vortex-like (trapped) ion distribution on dust-acoustic (DA) solitary waves (SWs) propagating in SGOPDP medium. The reductive perturbation method, which is valid for small but finite amplitude SWs, is employed to derive a modified Korteweg-de Vries equation having stronger nonlinearity. The basic features of the DA SWs in SGOPDP medium are found to be significantly modified by the combined effect of self-gravitational field and vortex-like ion distribution. The results of this paper have many implications in space and laboratory dusty plasmas.