Dust-acoustic Mode Research Articles

Ultra-low-frequency electrostatic waves in a self-gravitating magnetized and inhomogeneous dusty plasma

Obliquely propagating ultra-low-frequency electrostatic waves in a self-gravitating uniformly magnetized and inhomogeneous dusty plasma are investigated using the gyro-kinetic theory for the dynamics of the charged dust grains, ions and electrons. The modes are found to be unstable under certain conditions. It is noticed that when the perpendicular phase velocity of the mode is higher than the dust-drift velocity V Dd, ( ω/ k↑ ≫ V Dd), the modified dust-acoustic mode due to gravity suffers Jeans instability and when ω/ k↑ < V Dd, the modified dust-drift mode suffers universal instability which is due to the diamagnetic drift of dust particles. The implications of this result for some space and astrophysical situations are also indicated. © 1999 Elsevier Science Ltd. All rights reserved.

Surface Waves in a Dusty Plasma

Electrostatic low frequency surface modes propagating along aninterface between a dusty plasma and vacuum with frequencies of theorder of the dust plasma frequency are investigated using a fluidmodel where the dust dynamics and dust charge fluctuations are takeninto account. The dispersion properties and damping of these dustacoustic surface modes due to charge fluctuation effects arederived.

Low frequency modes in strongly coupled dusty plasmas

The influence of strong correlations on low frequency collective modes in a dusty plasma is investigated. The dust dynamics is modeled by the generalized hydrodynamics description. For the well known dust acoustic mode, strong correlations lead to new dispersive corrections, an overall reduction of the frequency and phase velocity and the existence of parameter regions where ∂ω/∂k&amp;lt;0. A novel result is the possibility of sustaining a low frequency transverse mode—a dust shear mode—in which the correlation energy acts as an effective bulk modulus. The influence of ion streaming and collisional interaction with a background of neutrals on the modes are also studied and it is shown that the longitudinal modes may be driven unstable by ion streaming.

Laboratory studies of waves and instabilities in dusty plasmas

Theoretical and experimental studies of low-frequency electrostatic waves in plasmas containing negatively charged dust grains are described. The presence of charged dust is shown to modify the properties of ion-acoustic waves and electrostatic ion-cyclotron waves through the quasineutrality condition even though the dust grains do not participate in the wave dynamics. If the dust dynamics is included in the analysis, new “dust modes” appear—dust acoustic and dust cyclotron modes. The results of laboratory experiments dealing with dust ion acoustic (DIA) waves and electrostatic dust ion cyclotron (EDIC) waves are shown. These modes are more easily excited in a plasma containing negatively charged dust. Finally, observations of dust acoustic (DA) waves are presented and measurements of the dispersion relation are compared with one obtained from fluid theory.

Comment on “Is dust acoustic wave a new plasma acoustic mode?” [Phys. Plasmas 4, 3427 (1997)

Dwivedi’s claim [Phys. Plasmas 4, 3427 (1997)] that the dust-acoustic wave should not be viewed as a novel plasma wave is rebutted. The so-called acoustic-like mode introduced earlier by Dwivedi et al. [J. Plasma Phys. 41, 219 (1989)] rests physically on very dubious grounds, because it considers a plasma with two ion species in the presence of a fixed electron background. In addition, Dwivedi et al. have nowhere included heavy charged dust grains as potential applications of their (flawed) theoretical treatment. Hence Rao et al. (1990) were indisputably the first ones to point out the possibility of dust-acoustic modes, correctly so, as we argue, because a distinct name is fully justified by the enormous order-of-magnitude differences in the charge-to-mass ratios of the usual charged dust grains compared to “ordinary” ions and by the recent experimental verification.

Acoustic modes in a dusty plasma

Abstract The propagation of the dust ion acoustic and dust acoustic modes in a dusty plasma is studied. The effect of the coupling of the charge fluctuation on the dust particles to the modes is taken into account self-consistently. It is found that the charge fluctuation leads to frequency down shift as well as dissipation of the modes. For the dust ion acoustic modes, these are significant only when the frequency characterizing the rate of capture of electrons by the dust particles in the equilibrium state is of the order of the frequency of the mode, and the mode can propagate without significant dissipation only when its frequency is well above this characteristic frequency. For the dust acoustic modes, these are significant only when the frequency characterizing the rate of capture of ions by the dust particles in the equilibrium state is of the order of the frequency of the mode, and the mode can propagate without significant dissipation only when its frequency is well above this characteristic frequency.

Dust-acoustic waves in a magnetized dusty plasma

The modification and damping of the dust-acoustic wave in a uniformly magnetized dusty plasma have been investigated using the Vlasov-kinetic model for the plasma with dust particles as a third component having average constant charge and mass. It is noticed that for the strong finite Larmor radius (FLR) effect, the frequency and damping of the mode depend significantly on the magnetic field and they are independent of the magnetic field for the case of weak FLR effect. For exact transverse propagation (k‖=0), the dust-acoustic mode ceases to exist, however, a new mode known as the “dust-lower-hybrid” mode comes into play in the hot magnetized dusty plasma.

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.

Ionization instability in dusty plasmas

The ionization instability in a dusty plasma in which the neutral gas is ionized by a constant flux of energetic electrons with energy slightly above the ionization energy is examined by using fluid equations for the three charged components, namely positive ions, electrons, and negatively charged dust grains. The presence of negatively charged dust increases both the frequency and the growth rate of the IA (ion-acoustic) wave excited through the ionization instability. The DA (dust-acoustic) mode, even in the absence of ion–neutral collisions, ion viscosity, and neutral gas drag on the dust grains, is always damped within the parameter ranges explored here and relevant to laboratory plasmas. The present results on the DA wave excitation are at variance with results obtained by Shukla and Morfill [Phys. Lett. A 216, 153 (1996)].

Radio wave scattering by dust-acoustic waves in a dusty space plasma

It is shown that weakly damped dust-acoustic modes result in an additional maximum in the scattering spectrum. The possibilities of determining dusty plasma parameters from radio wave scattering experiments in space are discussed.

Influence of dust mass distributions on generalized Jeans-Buneman instabilities in dusty plasmas

The linear dispersion law is given for a generalized Jeans-Buneman instability in the presence of a dust mass distribution. It is shown that this instability is easier to evoke when a reasonable power law mass distribution for the dust grains is assumed than for the mono-sized dust case. For Boltzmann distributed ions and electrons the dust-acoustic mode and the unstable Jeans mode are modified due to the self-gravitation and mass distribution. The frequency of the dust-acoustic mode is increased. For long wavelengths, a new stable mode occurs, due only to the dust mass distribution. The growth rate of the Jeans instability is increased, and the mode is extended beyond the usual wavelength domain. For high values of k a new instability arises, which is called the dust distribution instability.

Electron-temperature-gradient driven dust-acoustic waves in collisional dusty magnetoplasmas

It is shown that dust-acoustic and dust ion-acoustic waves can become unstable in the presence of an equilibrium electron-temperature-gradient (ETG) in a collisional dusty magnetoplasma. The growth rate of the ETG-driven dust-acoustic modes is obtained. It is found that nonthermal dust-acoustic fluctuations can cause cross-field anomalous electron diffusion and electron thermal transport in dusty plasmas. The relevance of our investigation to laboratory plasmas is pointed out.

Kelvin-Helmholtz instability driven by sheared dust flow

Stability analysis of the dust-acoustic mode in a magnetized three-component dusty plasma is carried out for both positively and negatively charged dust. Critical shears required to excite Kelvin-Helmholtz instability are obtained as a function of the ratio of dust charge density to ion charge density in equilibrium. It is found that the relative velocity between adjacent layers of the dust fluid should be at least equal to the dust-acoustic phase velocity in order that the instability is excited.