Particles In Complex Plasma Research Articles

Changes in the surface structure of melamine-formaldehyde particles in complex plasma

The surface modification of polymer microspheres by complex plasma was studied. Melamine-formaldehyde spherical microparticles, falling into neon dc glow discharge, acquired an electric charge on their surface and hung in a dust trap, where the electric field strength was strong enough. They were long trapped, forming three-dimensional ordered structures. Depending on the exposure time, the particle sizes and surface properties changed. Scanning electron microscopy provided insight in the particle morphology changing. The dependence of the particle size on the exposure in plasma was measured; the modification of the surface structure was investigated. The results of the statistical processing of the surface structure are presented.

Sound speed and diffusion in 2D Yukawa liquids: Effect of dipole–dipole interaction

The two‐dimensional (2D) Yukawa liquid with an additional screened dipole–dipole interaction is considered in connection with the 2D system of charged dust particles in complex plasmas. Particularly, the sound speed and diffusion in the case the Yukawa interaction potential dominant over the screened dipole–dipole interaction are analysed. Increase in the value of the sound speed and suppression of the super‐diffusion due to the additional dipole–dipole interaction are reported. This effect is explained by the stronger inter‐particle correlations induced by the additional dipole–dipole interaction.

Driving force for a nonequilibrium phase transition in three-dimensional complex plasmas

An example of the non-equilibrium phase transition is the formation of lanes when one kind of particle is driven against the other. According to experimental observation, lane formation in binary complex plasmas occurs when the smaller particles are driven through the stationary dust cloud of the larger particles. We calculate the driving force acting on a probe particle that finds itself in a quiescent cloud of particles in complex plasma of the low-pressure radio frequency discharge under microgravity conditions. It is shown that the nonzero driving force is a result of the dependence of the ion mean free path on the particle number density. If this effect is properly included in the model of similar complex plasmas, then one arrives at the driving force that changes its sign at the point where the probe and the dust particles have equal radii. If the probe is smaller than the dust particle, then the driving force is directed toward the discharge center and vice versa, in accordance with the experiment. The obtained results can serve as the ansatz for future investigation of the lane formation in complex plasmas.

An experimental study of the degradation of particles in complex plasma

Changes of melamine–formaldehyde resin (MF-R) particles occurring in complex dusty plasma have been investigated. Using a specially developed method, plasma-modified MF-R particles have been extracted from a dust trap after levitation for various periods of time and studied by electron microscopy techniques. Changes in the surface structure of MF-R particles are determined, and quantitative data on the variation in particle dimensions depending on the time of occurrence in plasma are obtained.

Solution of the inverse Langevin problem for open dissipative systems with anisotropic interparticle interaction

Solution of the inverse Langevin problem is presented for open dissipative systems with anisotropic interparticle interaction. Possibility of applying this solution for experimental determining the anisotropic interaction forces between dust particles in complex plasmas with ion flow is considered. For this purpose, we have tested the method on the results of numerical simulation of chain structures of particles with quasidipole-dipole interaction, similar to the one occurring due to effects of ion focusing in gas discharges. Influence of charge spatial inhomogeneity and fluctuations on the results of recovery is also discussed.

Measurement of net electric charge and dipole moment of dust aggregates in a complex plasma.

Understanding the agglomeration of dust particles in complex plasmas requires knowledge of basic properties such as the net electrostatic charge and dipole moment of the dust. In this study, dust aggregates are formed from gold-coated mono-disperse spherical melamine-formaldehyde monomers in a radiofrequency (rf) argon discharge plasma. The behavior of observed dust aggregates is analyzed both by studying the particle trajectories and by employing computer models examining three-dimensional structures of aggregates and their interactions and rotations as induced by torques arising from their dipole moments. These allow the basic characteristics of the dust aggregates, such as the electrostatic charge and dipole moment, as well as the external electric field, to be determined. It is shown that the experimental results support the predicted values from computer models for aggregates in these environments.

Effect of electron accretion by quantum tunneling on charging of dust particles in complex plasmas

This investigation explores the impact of the accretion of electrons on the dust particles through quantum tunneling on the charging of the dust particles in dark complex plasmas. With deference to the openness nature of complex plasmas, this analysis is based on the charge balance over dust particles and number/energy balance of electrons and ionic species. An expression for the mean energy associated with electrons, accreting through quantum tunneling has been derived and used in the kinetics. The difference between the predictions of the present analysis and the semi classical treatment has been graphically illustrated. It is seen that the electron accretion through tunneling appreciably affects the charging of the dust particles, and the mechanism is important for small radius (∼10nm) and number density (<103cm-3) of the dust particles and high electron density/temperature.

Stochastic heating of dust particles in complex plasmas as an energetic instability of a harmonic oscillator with random frequency

The paper describes the occurrence of stochastic heating of dust particles in dusty plasmas as an energy instability due to the correlations between dust grain charge and electric field fluctuations. The possibility that the mean energy (“temperature”) of dust particles can grow in time has been found both from the self-consistent kinetic description of dusty plasmas taking into account charge fluctuations [U. de Angelis, A. V. Ivlev, V. N. Tsytovich, and G. E. Morfill, Phys. Plasmas 12(5), 052301 (2005)] and from a Fokker-Planck approach to systems with variable charge [A. V. Ivlev, S. K. Zhdanov, B. A. Klumov, and G. E. Morfill, Phys. Plasmas 12(9), 092104 (2005)]. Here, a different derivation is given by using the mathematical techniques of the so called multiplicative stochastic differential equations. Both cases of “fast” and “slow” fluctuations are discussed.

Statistical mechanics of the distribution of charge on particles in complex plasmas

This paper presents an analytical study of the distribution of charge on the particles in a complex plasma; the study is based on statistical mechanics and ensures that the charge on the particles is an integral multiple of the electronic charge. The formulation incorporates both the number and energy balance of electrons/ions. Three specific cases of charging of particles have been considered, namely (i) in a plasma in the absence of electron emission from the particles, (ii) in a complex plasma in thermal equilibrium and (iii) in a complex plasma irradiated by monochromatic radiation, causing photoelectric emission of electrons from the particles. The effect of various parameters on the charge distribution has also been investigated. This paper is in reasonably good agreement with the fluctuation theory for large values of Z (Ze is the charge on a particle). It is seen that under certain conditions, a significant number of oppositely charged particles occur in the complex plasma.

Critical point and sound waves in complex plasmas

An equation of state for particles in complex plasmas, which includes contributions from plasma background fields and interparticle interactions (electric repulsion and “ion shadow” attraction), is obtained. Using this equation, experimental parameter regimes for the observation of liquid-vapor transitions and a critical point are examined. In addition, it is demonstrated that as in binary fluids, sound waves in complex plasmas do not exhibit critical behavior. Thus, criticality in complex plasmas may have more in common with binary fluids rather than ordinary fluids.

Mean-Field Theory of Critical Phenomenon for Mutually Repelling Particles in Complex Plasmas

A mean-field theory of criticality for charged particles in complex plasmas is proposed. It is shown that the existence of the critical point and the liquid-vapor coexistence is fully consistent with a purely repulsive potential between particles; the cohesive field due to the plasma background drives these. The critical exponents, calculated by expanding the free energy near the critical point, are found to be classical. The phase coexistence curve, obtained by minimizing Gibbs potential, is similar to that of other mean-field models, e.g., van der Waals fluids, ionic fluids, etc. These results lend support to the concept of "universality" in widely different systems.

Secondary electron emission of carbonaceous dust particles

In this paper we present measurements of the secondary electron emission yield (gamma) of a carbonaceous dust particle material, which was grown in argon diluted acetylene plasmas. One aim was to reach a better understanding of charging and discharging processes of dust particles in complex plasmas due to secondary electron emission and consequently to try to explain the anomalous behavior of electron density observed in afterglows of pulsed rf plasmas. We compared the results of a simple model and of a Monte Carlo simulation to the previously measured time dependence of the electron density in complex plasma afterglow. It was found that the value of the intrinsic secondary electron yield from the carbonaceous dust material is too low to explain the increase of electron density in the afterglow. It is, however, possible that the electrons charging the particles are weakly attached so that they may be released with high efficiency by ion bombardment due to field induced emission or by other mechanisms.

Vertical oscillations of paramagnetic particles in complex plasmas.

Vertical vibrations of a single magnetized dust grain and a one-dimensional string of magnetized particles in discharge plasmas are treated taking into account the magnetic force associated with gradients of an external magnetic field. For a single particle a novel type of oscillation associated with these gradients is found. Such vibrations can be stable or unstable depending on the distribution of the magnetic field inside the particle cloud. In a one-dimensional particle string the magnetic force causes a new low-frequency oscillatory mode which is characterized by inverse optical-like dispersion when the wavelength far exceeds the intergrain distance. The study of vertical vibrations of magnetized grains provides a tool for determining complex plasma parameters.

Note on the charging and spinning of dust particles in complex plasmas in a strongmagnetic field

Qualitative analysis of two new effects related to theinfluence of a strong magnetic field on the state of complex dusty plasmas is given. First, it is shown that the dust shapeasymmetry, together with the presence of plasma charging flux,creates an angular momentum flux on a dust grain causing itsrotation. The value of the estimated angular velocity is comparedwith that already observed. The magnetic moment related to the balance of the angular momenta transfer by plasma flux and thefriction on neutrals is estimated. It is estimated that theinteractions of these magnetic moments are usually much weakerthan the Coulomb interactions. Apart from the magnetic momentsinduced by plasma flux the dust grain can have an intrinsicmagnetic moment. Both of them create an average magnetization in complex plasmas. Second, it is shown that an increase in anexternal magnetic field first decreases the dust charges (whenthe electrons in the charging process start to be magnetized)and then, with a further increase of the magnetic field, thedust charges increase (when the ions in the charging process start to bemagnetized). Only the limiting cases of strong electron and ionmagnetization are discussed.

Mutual interactions of magnetized particles in complexplasmas

Various mutual dust-dust interactions in complex plasmas,including the forces due to induced magnetic and electricmoments of the grains are discussed. It is shown that the dipoleshort-range forces can be responsible for the formation offield-aligned chains. Such chains may incorporate a few tens ofindividual particles, as frequently observed in experiments.