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.

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.

Kinetics of ensembles with variable charges.

Kinetics of particle ensembles with variable charges is investigated. It is shown that the energy of such ensembles is not conserved in the interparticle collisions. The case when the equilibrium charge depends on the particle coordinate is studied, and the collision integral describing the momentum and energy transfer in collisions is derived. Solution of the resulting kinetic equation shows that the system is unstable--the mean thermal energy exhibits explosion-like growth, diverging at a finite time.

Theory of dust and dust-void structures in the presence of the ion diffusion.

A dust void is a dust-free region inside the dust cloud that often develops for conditions relevant to plasma processing discharges and complex plasma experiments. A distinctive feature of the void is a sharp boundary between the dust and dust-free regions; this is manifested especially clear when dissipation in the plasma is small and discontinuity of the dust number density appear. Here, the structure of the dust void boundary and the distribution of the dust and plasma parameters in the dust structure bordering the void is analyzed taking into account effects of dissipation due to the ion diffusion on plasma neutrals. The sharp boundary between the dust and void regions exists also in the presence of the ion diffusion; however, only derivatives of the dust density, dust charge, electron density and electric field are discontinuous at the void boundaries, while the functions themselves as well as derivatives of the ion drift velocity and the ion density are continuous. Numerical calculations demonstrate various sorts of diffusive dust void structures; the possibility of singularities in the balance equations caused by the diffusion process inside the dust structures is investigated. These singularities can be responsible for a new type of shocklike structures. Other structures are typically self-organized to eliminate the singularities. Numerical computations in this case demonstrate a set of thin dust layers separated by high density thin dust clouds similar to the multiple-layer dust structures observed in the laboratory and in the upper ionosphere. The possibility for existence of a few equilibrium positions of the void boundary is discussed.

Spectral properties of small dusty clusters.

A monolayer dusty crystal can be observed in the glow discharge. In particular, a small number of dusty grains form simple atom-like plane clusters. Stability and oscillations of the polygonal cluster are considered. For the simplest stable clusters normal displacements and frequencies are found for an arbitrary form of mutual interaction. The measurement of these modes can help to give in detail the form of the potential function.

Theory of collision-dominated dust voids in plasmas.

A dust void, i.e., the dust-free region in a dusty plasma, results from the balance of the electrostatic and plasma (such as the ion drag) forces acting on a dust particle. The properties of dust voids depend on the ratio of the void size to the mean free path of plasma ions colliding with neutral species of a weakly ionized plasma. For many plasma-processing and plasma-crystal experiments, the size of the void is much larger than the ion-neutral mean free path. The theory and numerical results are presented for such a collisional case including the situations in which the plasma is quasineutral in the void region or the plasma quasineutrality is violated, as well as the case in which the ion ram pressure is insignificant.

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.

Shielding and charging of dust particles in the plasma sheath.

General physical features of the ion particle distribution function in the plasma sheath derived theoretically and observed experimentally are used for describing the dust shielding and charging in the sheath. It is shown that the shielding and charging of dust depend strongly on the degree of anisotropy of the ion distribution function and on the difference in the ion temperatures parallel and antiparallel with respect to the ion flow. Regions of "antishielding" appear both along the ion flow and perpendicular to it. The potential wells can be responsible for the attraction of other dust particles and for the creation of dust aggregates. This effect is related to the change of the sign of the dielectric function in the range of wave vectors corresponding to the strong Landau damping.