Shear banding in mesoscopic dusty plasma liquids

We experimentally demonstrate shear banding and construct a microscopic dynamic picture of a sheared 2D mesoscopic dust Coulomb liquid at the kinetic level. Under the topological constraints from the discreteness and finite boundary, the nonlinear threshold-type response of motion to the local stress induced by thermal and external drives leads to shear thinning and the enhanced avalanche-type local topological transitions with stress relaxation in the form of clusters. It causes the formation of the outer shear bands in which the mean shear rate, the velocity fluctuations, and the structural rearrangement rate are all enhanced, and leaves a weakly perturbed center band. The typical size of the cooperative hopping vortex (about three interparticle distance) sets up a common length scale for the widths of the confinement induced layering and the shear band.     

Jeans-Buneman instability in a dusty plasma

A self consistent formulation of the Jeans instability of a dusty plasma with proper inclusion of charge dynamics is described. It is shown that charge fluctuations significantly affect the Jeans as well as the Buneman mode. For plasma particles (electrons and ions) in local thermal equilibrium, the Jeans lengthλ _J is given byλ _J≈λ _g F(R, ε, β/η), whereλ _g is the Debye length of the charged grains,R is the square of the ratio of the Jeans to the plasma frequency of the grains,ε is the square of the ratio of the Debye length of the grains and the plasma particles andβ/η is the ratio of the attachment to the decay frequency of the electronic charges to the grain surface. The functional form ofF is given in the text. Numerical investigation of the Jeans-Buneman mode for a two and three component plasma shows that the Jeans mode dominates atkλ _D≪1 (wherek is the wave number andλ _D is the Debye length of plasma particles), whereas atkλ _D≫1 only the Buneman mode operates. Charge fluctuations reduce the area of overlap of the two modes. Furthermore, in the absence of gravity, there exists a new, charge fluctuation induced unstable mode in a streaming dusty plasma. Astrophysical applications of the results are discussed.     

Three-particle correlations in nonideal dusty plasma

Results are given of experimental investigation of three-particle correlations for liquid plasma-dust structures formed in the electrode layer of a high-frequency capacitive discharge. The obtained three-particle correlation functions for experimental and numerical data are analyzed and compared with the superposition approximation. The forming of clusters of macroparticles in plasma-dust systems being analyzed is revealed.     

Crystallization waves in a dusty plasma

Crystallization waves in the dusty component of a complex plasma, which were recently observed experimentally, have been investigated numerically. The evolution of the system of charged microparticles whose interaction between each other is described by a screened Coulomb potential (Yukawa potential) has been numerically simulated using the molecular dynamics method. It has been shown that the process of the formation and propagation of a crystallization wave in such a system is fundamentally three-dimensional. Analysis of the local structure of dust particles behind the crystallization wave front indicates the coexistence of different types of the crystal lattice including the metastable phase, i.e., a nonequilibrium phase transition.     

Acoustic modes in a dusty plasma

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.     

Manifestation of polarization effects in dusty plasma

This paper is devoted to a detailed analysis of polarization effects in dusty plasma (DP). They are shown to lead to a nonmonotone decay of the self-consistent potential near the macroparticle, which may result in the formation of regular structures in the DP.     

Thermal condensation mode in a dusty plasma

In the present work, the radiative condensation instability is investigated in the presence of dust charge fluctuations. We find that the charge variability of the grain reduces the growth rate of radiative mode only for fluctuation wavelength smaller or of the order of the Debye length and this reduction is not very large. Far from the Debye sphere, radiative mode can damp due to thermal conduction of electrons and ions     

Laser-particulate interactions in a dusty RF plasma

The interaction of particulates formed in an argon RF discharge containing 1-5% CCl₂F₂ admixture with a pulsed infrared laser (Nd:YAG, intensity ~10⁹ W m^-2, pulse duration ~10^-4 s) has been studied in situ. The white light emitted during this process has been monitored as a function of time and wavelength using a fast photo diode and an optical multichannel analyser. The spectra have been fitted with blackbody curves with a standard deviation of 5%. A spectral temperature of about 3500 K has been obtained for various plasma conditions and attributed to the decomposition temperature of the particulate material. A model based on laser heating, internal heat conduction and chemical decomposition is compared with the experimental results. This model predicts the time constants for heating and decomposition of the particulates and explains the dependence of the measured emission intensity on the laser intensity     

Cherenkov radiation waves in inhomogeneous dusty plasma

A kinetic theory is employed to study Cherenkov wave in an inhomogeneous dusty plasma. Two different frequency regimes are considered incorporating the plasma species temperatures. The dispersion relation for one-dimensional Cherenkov wave is derived and analyzed. The plasma species temperatures, their cyclotron frequencies, and the plasma density inhomogeneity effect the growth/damping of Cherenkov waves. It is shown that the plasma inhomogeneity contributes to damping of Cherenkov waves.     

Viscosity of a dusty plasma liquid

We present the results of our experimental study of the flow of a dusty plasma liquid produced by macroparticles in an argon plasma. The dependences of shear viscosity for such a liquid on the magnitude of the external force inducing the dusty plasma liquid flow and on the plasma-generating gas pressure are analyzed. We have established that the viscosity of a dusty plasma medium decreases with increasing shear stress in it, while the viscosity of such a liquid increases with buffer gas pressure. The flow of a dusty plasma liquid under the action of an external force has been found to resemble the plastic deformation of a Bingham body. We suggest that the formation of crystal-like dusty plasma clusters in a “liquid” phase can be responsible for the non-Newtonian behavior of the dusty plasma liquid flow.     

Supernonlinear ion-acoustic waves in a dusty plasma

An exact solution is obtained for the equations that describe nonlinear ion-acoustic waves in a dusty plasma. It is shown that the solution can be in the form of nonlinear periodic waves, solitons, and supernonlinear waves whose trajectories envelope one or several separatrices in the phase portrait of the wave. Profiles of physical quantities in the wave are constructed. The supernonlinear waves are shown to be of two types, subsonic (type 1) and supersonic (type 2). Existence regions of supernonlinear waves of both types and solitons are constructed in the plane of the problem parameters.     

Wake potential in a self-gravitating dusty plasma

Using a test particle approach, the dynamical wake potential has been examined in a homogeneous self-gravitating dusty plasma. The periodic oscillatory potential might lead to an alternative approach to the Jeans instability for the formation of dust agglomeration leading to gravitational collapse of the self-gravitating systems.     

Coagulation of charged particles in a dusty plasma

An investigation is made of characteristic features in the behavior of small particles in a dusty plasma attributable partly to the suppression of coagulation as a result of monopolar charging for particle sizes smaller than the Debye shielding length and partly to the reduction in the effect of charging for larger particles. Similarity relations linking the plasma composition and particle charge with the parameters of the dust component are used to determine the range of parameters for which the linear approximation of the particle charge as a function of their sizes holds. A modified classical theory of coagulation in the diffusion approximation is used to study some anomalies in the behavior of the particle size distribution. It is established that unlike an ordinary aerosol, in a dusty plasma the dispersion of the distribution and the average particle size may decrease with time. It is shown for the first time that a long-lived “quasi-liquid” state of a dusty plasma may be established as a result of the anomalous behavior of the size distribution function of coagulating charged particles.     

The effect of magnetic field on plasma particles in dusty plasma

In this work, we present the investigation of the formation features and internal structure of dust clouds created in plasma of glow discharge in the external magnetic field corresponding to a range of moderate and strong fields, at which the ion component is magnetized. The analysis of the plasma magnetization in the presence of dust components is carried out. We defined the values of magnetic induction at which the changes in dynamics of plasma particles in magnetic field in light inert gases are expected. The experimental setup was built in two versions. For the purpose of generating of magnetic field, the first setup was equipped with ordinary magnetic coils, and the second one included a superconducting solenoid. The discharge tubes, the main chambers where plasma was ignited and maintained in a glow discharge in lowered pressure, also have certain peculiarities, which we describe below. While using helium as a bulk gas, our study focused only on the dust trap in the region of narrowing discharge current. For neon, we used two traps: the striation trap and one just mentioned above placed in the narrowing of the discharge tube. As a result, the steady dust structures in a glow discharge under the magnetization of ions and electrons were obtained for the first time. Dust structures were rotated and tended to form a dust cluster and shell structure. A number of parameters of magnetization achieved in experiments were calculated.     

Rotation of a single vortex in dusty plasma

A single vortex is obtained in radio-frequency capacitive discharge in argon gas. The dust subsystem is confined in the horizontal plane with an asymmetrical saw structure placed on the lower electrode. The vortex rotates as a whole along the long side of the saw-teeth. Asymmetry of the saw structure plays an important role in the rotation of the vortex. Nonzero curl of the total force resulting from the local ion flow and the electric field in the plasma sheath could be attributed to the persistent rotation of vortex.     

Physical forces exerted by microbubbles on a surface in a traveling wave field

The effect of a wave with a varying traveling component on the bubble activity as well as the physical force generated by microbubbles on a surface has been studied. The acoustic emission from a collection of bubbles is measured in a 928 kHz sound field. Particle removal tests on a surface, which actually measures the applied physical force by the bubbles on that surface, indicate a very strong dependence on the angle of incidence. In other words, when the traveling wave component is maximized, the average physical force applied by microbubbles reaches a maximum. Almost complete particle removal for 78 nm silica particles was obtained for a traveling wave, while particle removal efficiency was reduced to only a few percent when a standing wave was applied. This increase in particle removal for a traveling wave is probably caused by a decrease in bubble trapping at nodes and antinodes in a standing wave field.     

Radar studies of ionospheric dusty plasma phenomena

We discuss the influence of charged dust on radar observations in the Earth ionosphere. This region in the upper Earth atmosphere can be described as a partially ionized, low‐temperature plasma. Plasma parameters vary by orders of magnitude spatially and in time. Dust particles influence the charge balance, in some cases dusty plasma condition is met. The polar mesospheric echoes are an example of dust plasma interactions observed with radar. The mesosphere is a region where atmospheric temperature decreases with altitude and can reach frost point temperature. The formation of the polar mesospheric radar echoes involves neutral atmosphere dynamics, which is latitude dependent and it involves charged dust particles, especially icy dust that forms in the polar summer mesosphere. Charged dust can also influence incoherent scatter that results from electromagnetic waves scattering off electrons, where the electrons are coupled to other charged components. Observers rarely report charged dust signatures in the incoherent scatter spectra; we show that there is a good chance for doing so with improved observations. The incoherent scatter can possibly also be used to estimate the amount of charged dust in the direct vicinity of a meteor, as we show based on the order of magnitude considerations. This prospect of new observational results makes theoretical investigations of radio‐wave scattering in the presence of charged dust with size distributions worthwhile.     

Three-dimensional wake potential in a streaming dusty plasma

The oscillatory wake potential for a slowly moving or static test dust particulate in a finite temperature, collisionless and unmagnetized dusty plasma with a continuous flow of ions and dust particles has been studied. The collective resonant interaction of the moving test particle with the low-frequency and low-phase-velocity dust-acoustic mode is the origin of the periodic attractive force between the like polarity particulates along and perpendicular to the streaming ions and dust grains resulting into dust-Coulomb crystal formation. This wake potential can explain the three-dimensional dust-Coulomb crystal formation in the laboratory conditions.     

Impurity-induced local modes in one-dimensional dusty plasma chains

The effects of impurity on eigenmodes in one-dimensional dusty plasma lattices are studied.It is found that local modes can be excited besides lattice waves,due to the existence of an impurity particle.The dispersion relations of the modes are derived accordingly.Properties of the lattice and local modes are also analyzed and discussed,particularly for their symmetric features and conditions of the mode excitation.