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The microstructure of a strongly coupled liquid undergoing a shear flow was studied experimentally. The liquid was a shear melted two-dimensional plasma crystal, i.e., a single-layer suspension of micrometer-size particles in a rf discharge plasma. Trajectories of particles were measured using video microscopy. The resulting microstructure was anisotropic, with compressional and extensional axes at around $\ifmmode\pm\else\textpm\fi{}45\ifmmode^\circ\else\textdegree\fi{}$ to the flow direction. Corresponding ellipticity of the pair correlation function $g(\mathbf{r})$ or static structure factor $S(\mathbf{k})$ gives the (normalized) shear rate of the flow.

International audience; A simple method of characterization of suspensions of spherical nanoparticles with monotonically variable size is proposed. It allows for the in situ measurement of the particle size as well as spectral dependence of their refractive indices. The method requires three optical channels: one for the illumination of a suspension by white light and two for the measurements of the spectra of scattered light. Parameters of the particles are determined by fitting the measured temporal spectral surfaces by the calculated Mie scattering functions. The method is applied to the particles being grown in a low-pressure reactive plasma of a discharge in an acetylene-argon mixture

In the recent years, non-Gaussianity and statistical isotropy of the Cosmic Microwave Background (CMB) was investigated with various statistical measures, first and foremost by means of the measurements of the WMAP satellite. In this Review, we focus on the analyses that were accomplished with a measure of local type, the so-called Scaling Index Method (SIM). The SIM is able to detect structural characteristics of a given data set, and has proven to be highly valuable in CMB analysis. It was used for comparing the data set with simulations as well as surrogates, which are full sky maps generated by randomisation of previously selected features of the original map. During these investigations, strong evidence for non-Gaussianities as well as asymmetries and local features could be detected. In combination with the surrogates approach, the SIM detected the highest significances for non-Gaussianity to date., 19 pages, 15 figures, Review Article, Accepted for publication in Advances in Astronomy

We demonstrate that the melting curves of various model systems of interacting particles collapse to (or are located very close to) a universal master curve on a plane of appropriately chosen scaled variables. The physics behind this universality is discussed. An equation for the emerging “universal melting curve” is proposed. The obtained results can be used to approximately predict melting of various substances in a wide range of conditions.

Summary form only given. Solids and liquids consist of molecules whose microscopic arrangement affects the macroscopic properties of the matter. It is very difficult or impossible to follow the motion of molecules in real time at the microscopic scale. Here we use a model system - complex plasma, where due to its slow relaxation time and large spatial scale, individual particles can be observed in real time. Complex plasmas consist of micron-sized plastic spheres (grains) mixed with an ion-electron plasma. The grains can be levitated and confined in a low pressure gas discharge, where they form liquid- and solid-like structures, undergo phase transitions, propagate waves, solitons, shocks and exhibit other dynamic effects.

In an experiment performed on the International Space Station using the PK-3 Plus instrument, 3.4-micron plastic microparticles were introduced in a neon glow discharge plasma. The microparticles became negatively charged and were confined by ambipolar electric fields. Using laser illumination and video cameras, microparticles were imaged and their motions were tracked using image analysis software. We calculate the velocity distribution function f(v) for the random motion. We find that f(v) is non-Maxwellian with an elongated high-energy tail for this non-equilibrium system and f(v) is fit well by the Tsallis distribution. This distribution is popular in the field of statistical physics for non-equilibrium systems.

Freezing and melting of large three-dimensional complex plasmas under microgravity conditions is investigated. The neutral gas pressure is used as a control parameter to trigger the phase changes: Complex plasma freezes (melts) by decreasing (increasing) the pressure. Evolution of complex plasma structural properties upon pressure variation is studied. Theoretical estimates allow us to identify main factors responsible for the observed behavior., Phys. Rev. Lett. (in press); 4 pages, 4 figures

Low-pressure room-temperature neon, argon, krypton, and air plasmas were studied in magnetic fields up to flux densities of 2.3 T. Filaments appeared parallel to the magnetic field lines, and patterns such as spirals and concentric circles formed in the perpendicular direction. We link these effects to the magnetization of the ions. We also used a layer of embedded microparticles as probes in the plasma. Their motion changed dramatically from a collective rotation of the whole ensemble in moderate magnetic fields to a rotation in several small vortices centered at the filaments.

The particle charge has been calculated in collisional plasma in PK‐4 experimental facility. It is shown that ion‐neutral collisions play an important role to determine particle charge in this regime. Initially the grain charge decreases and later it increases with ion collisionality index. The experimental results agree well with the analytical model for grain charging.

We demonstrate that the melting curves of various model systems of interacting particles collapse to (or are located very close to) a universal master curve on a plane of appropriately chosen scaled variables. The physics behind this universality is briefly discussed. An equation for the emerging “universal melting curve” is proposed. The obtained results can be used to approximately predict melting of various substances (including complex plasmas) in a wide range of conditions.

The structural properties of dense random packings of identical hard spheres (HS) are investigated. The bond order parameter method is used to obtain detailed information on the local structural properties of the system for different packing fractions $\phi$, in the range between $\phi=0.53$ and $\phi=0.72$. A new order parameter, based on the cumulative properties of spheres distribution over the rotational invariant $w_6$, is proposed to characterize crystallization of randomly packed HS systems. It is shown that an increase in the packing fraction of the crystallized HS system first results in the transformation of the individual crystalline clusters into the global three-dimensional crystalline structure, which, upon further densification, transforms into alternating planar layers formed by different lattice types., Comment: 4 pages, 5 figures

Analyzing three approximate methods to locate liquid-solid coexistence in simple systems, an observation is made that all of them predict the same functional dependence of the temperature on density at freezing and melting of the conventional Lennard-Jones system. The emerging equations can be written as $T={\mathcal A}\rho^4+{\mathcal B}\rho^2$ in normalized units. We suggest to determine the values of the coefficients ${\mathcal A}$ at freezing and melting from the high-temperature limit, governed by the inverse twelfth power repulsive potential. The coefficients ${\mathcal B}$ can be determined from the triple point parameters of the LJ fluid. This produces freezing and melting equations which are exact in the high-temperature limit and at the triple point, and show remarkably good agreement with numerical simulation data in the intermediate region., Comment: 6 pages, 1 figure

We demonstrate the levitation of diamond fine particles in a H2 rf plasma chamber equipped with a hot filament and heated electrodes. The levitation conditions should be carefully chosen to compensate the strong thermophoretic forces caused by the filament and the electrodes. This levitation technique with the existence of a hot filament can be applied, e.g., for the efficient growth of diamond layers on seed particles injected and levitated in an rf plasma with reactive gases, e.g., CH4/H2. Additionally, the method for direct capture of levitated particles on a planar substrate was established, which is useful if it is necessary to analyze the particles after the levitation.

A micro-gravity experiment to study the growth of dust particles has been proposed to be flown on one of the Columbus precursor flights. The micro-gravity environment will allow for low collision velocities (of order of mm s−1) of the dust grains and for a large Knudsen number of the embedding gas; conditions expected in the early solar nebula. The outcome of the experiment will yield estimates of the sticking efficiency and the critical velocity for agglomeration. The values of these two parameters will provide substantial improvements in the constraints for models of the formation of planetesimals. In particular the questions related to growth rate and mode of the aggregation process will be answered. The range of material type, collision velocities, properties of the environment in which growth takes place, and other factors permit a natural extension of this experiment to take advantage of the capabilities of the space station Columbus. Other astrophysical applications, such as processes in Saturnian rings, with somewhat different regimes could also be investigated.

We describe, formulate, and investigate quantitatively a physical process which will lead to radial plasma transport in dusty planetary magnetospheres. The process depends on plasma inhomogeneities (in,particular electron temperature fluctuations) interacting with distributed fine-grained ring material to drive currents along the magnetic field lines, which close through the ionosphere. Azimuthal electric fields generated in this way will then lead to radial plasma flows via the E x B drift. The process is investigated both for Saturn's oxygen torus and for the Io torus in Jupiter's magnetosphere.

We suggest a model to explain the unexpected recurrent dust events that were observed during the Jupiter encounter by the dust detector on board the Ulysses spacecraft. This model is based dust-magnetosphere interactions. Dust particles inside the Jovian magnetosphere collect electrostatic charges and their interaction with the magnetic and electric fields can lead to energization and subsequent ejection. We discuss the dusty regions (ring/halo, `gossamer' ring) and also Io as potential sources for the Ulysses events. This model favors Io as a source. The mass and velocity range of the escaping particles are compatible with the observations, and we also suggest internal periodicities to explain the recurrent nature of the Ulysses dust events.

Using the PK-3 Plus laboratory onboard the International Space Station motion of a large projectile in the bulk of a dust crystal formed by negatively charged small particles was investigated. It is demonstrated that a subsonic projectile moves almost freely inside the dust crystal. A hydrodynamic theory of projectile nonviscous motion confirms the experimental data.

The aim of this chapter is to demonstrate that a complex plasma requires formulation of a new ground state with the balance of fluxes as an inevitable feature. The flux variation has a strong effect on the propagation of collective modes leading not only to the mode damping but also to an instability which leads to formation of structures in complex plasmas.

Dedicated experiments with strongly coupled complex plasmas in external electric fields were carried out under microgravity conditions using the PK-4 dc discharge setup. The focus was put on the comparative analysis of the formation of stringlike anisotropic structures due to reciprocal (hamiltonian) and nonreciprocal (non-hamiltonian) interactions between microparticles (induced by ac and dc fields, respectively). The experiments complemented by numerical simulations demonstrate that the responses of complex plasmas in these two regimes are drastically different. It is suggested that the observed difference is a manifestation of intrinsic thermodynamic openness of driven strongly coupled systems.

[1] We describe a new type of experiment where micrometer-size water ice particles are created from D2 and O2 in the plasma chamber, with the electrodes cooled by liquid nitrogen. In the reactor, D2 and O2 are decomposed by electron impacts and form precursors for chemical reactions. Water ice particles are produced within a second after plasma ignition. We propose a simple growth/sedimentation model, which reproduces the experimental data.

The speed-stress relation for gliding edge dislocations was experimentally measured for the first time. The experimental system used, a two-dimensional plasma crystal, allowed observation of individual dislocations at the "atomistic" level and in real time. At low applied stress dislocations moved subsonically, at higher stress their speed abruptly increased to 1.9 times the speed of shear waves, then slowly grew with stress. There is evidence that immediately after nucleation dislocations can move faster than pressure waves., 5 pages, 4 figures

The liquid-solid phase transition of the Lennard-Jones (LJ) system is investigated. It is found that the properly normalized second derivative of the interaction potential is practically constant at freezing. Using this relation a simple equation for the freezing curve is derived. The obtained equation is used to estimate the triple-point parameters of the LJ system. Results are compared with available numerical simulation studies.

Using experiments and combining theory and computer simulations, we show that binary complex plasmas are particularly good model systems to study the kinetics of fluid-fluid demixing at the "atomistic" (individual particle) level. The essential parameters of interparticle interactions in complex plasmas, such as the interaction range(s) and degree of nonadditivity, can be varied significantly, which allows systematic investigations of different demixing regimes. The critical role of competition between long-range and short-range interactions at the initial stage of the spinodal decomposition is discussed.

Health Care covers three areas of interest for cold atmospheric pressure plasmas: Cosmetics, Hygiene and Medicine. These areas can be subdivided into personal and professional care. In this review will concentrate on Hygiene and Medicine. In professional hygiene the most important plasma contribution is sterilization, decontamination and disinfection. The main aim is the prevention of diseases or their containment. Progress in the development of efficient bactericidal plasma sources has been rapid, so that it appears realistic to use plasmas to combat nosocomial infections as well as community associated infections in the not too distant future. The advantages of plasma devices - they use air and electricity only, there are no waste products, they are inexpensive to manufacture and operate, easy to transport and install, and bactericidal effects are fast (seconds). Plasmas can efficiently kill resistant bacteria (e.g. MRSA) and tests have shown no resistance build-up so far. With an estimated 2 Million hospital induced infections each year in the US alone, and about 100.000 resulting deaths, very efficient, safe and fast hospital plasma hygiene devices would appear to be a very important weapon to help contain the spread of infectious diseases. Similarly, containment in public places and services could be improved significantly using plasma hygiene devices. Last but not least comes food hygiene where the aim is to disinfect food for longer storage without harming tissue. At the personal level, plasma disinfection can play a role in household appliances, for the prevention and treatment of fungal diseases, for parodontosis and tetanus prophylaxy, to name but a few applications currently under discussion. There are first indications that plasmas can alleviate a number of skin irritations, too. In Medicine there are a number of ambitious ideas and aims. Plasmas can be "designed" to some extent. They can include different active species that can have an effect at the cellular level. There are ionic atoms and molecules, whose medical use need to be evaluated -the vision is that a new area of "plasma pharmacy" could develop. First steps are currently being taken in biological studies. Also the excited atoms in cold atmospheric plasmas may make cell walls more permeable for such species. This could be employed for distinguishing between different types of cells (e.g. cancer cells) and thus applying specific treatments at the cellular level. Of course, a word of caution is in order. Some issues seem straightforward and they will presumably lead the initial applications. Careful studies will be essential to understand the action of different plasmas on human cells, prokaryotic cells, viruses, spores, fungi to reap the benefits and avoid possible pitfalls. Other issues - like the plasma pharmacy -may be too complicated to achieve in the next two or three decades. But this is a grand challenge - chemical/biological pharmacy is an old subject and is nevertheless an area where major research is still essential.

Diagnostic methods are developed to measure plasma electron temperature T e and ion density n i . We do this without making any direct observations of the electrons or ions. Instead, we observe motion of microparticles, or dust, levitated in the plasma.

Recently, there has been enormous progress in plasma medicine. New groups have joined this area of research. New plasma devices have been developed and tested for biomedical applications. The difference in plasma production methods and composition of input gases does not allow to directly compare plasmas produced by various devices and predict their effect on biological systems.

The experiments performed onboard the International Space Station (ISS) demonstrate that a formation of homogeneous 3D dusty plasma structures under microgravity conditions is accompanied by the same difficulties as in laboratory. The plasma flows connected with plasma nonuniformity and a leaving of charged particles on walls lead to an appearance in the discharge center of a region free of dust grains, the so-called void. We present the analysis of the experiments performed onboard the ISS with the PKE-Nefedov facility when an additional low frequency (lf) voltage was applied to the electrodes. The sketch of the RF plasma chamber with the rf parallel plate discharge is well known. The aim of these experiments was an increase of a stability of dust structures and a void closure under an action of an external electric field. When the rf voltage amplitude increases the void axial size decreases and the radial size, on the contrary, increases. The void is being closed practically without a distortion of its form when the rf voltage on the electrodes decreases. The void boundary is sharp at all pressures analysed. When we apply the additional If voltage the void behavior is quite different a new additional force acting on the dust particle in the electrostatic trap generated by the averaged rf plasma fields modulated by the low frequency voltage appears. This force, as applied to the dust particles, was not considered previously. The force can be called as the force of the dynamical low frequency pressure by analogy with the force of the high frequency pressure which confines, for example, ions in the radio frequency Paul trap. This force appears due to the low frequency modulation of the grain equilibrium position in the nonuniform electric field of the trap. The amplitude of dust grains oscillations in the low frequency field does not exceed the interparticle distance and is about 200 microns. The dust grains are shifted under the action of this force in the direction of the weaker electric field that is to the trap center. When the amplitude of the low frequency modulation is comparable with the rf voltage amplitude on the electrodes, this force is comparable with the electric field force. This will serve to the void closure when the low frequency voltage is applied to the discharge. When the low frequency field is imposed on the rf discharge initially grains are shifted to the center from the regions with higher electric field. Consequently, the void starts to close from its boundary.

Dedicated experiments on melting of 2D plasma crystals were carried out. The melting was always accompanied by spontaneous growth of the particle kinetic energy, suggesting a universal plasma-driven mechanism underlying the process. By measuring three principal dust-lattice (DL) wave modes simultaneously, it is unambiguously demonstrated that the melting occurs due to the resonance coupling between two of the DL modes. The variation of the wave modes with the experimental conditions, including the emergence of the resonant (hybrid) branch, reveals exceptionally good agreement with the theory of mode-coupling instability., 4 pages, submitted to Physical Review Letters

Star formation occurs in dark molecular regions where the number density of hydrogen nuclei, nH, exceeds 10^4 cc and the fractional ionization is 10^-7 or less. Dust grains with sizes ranging up to tenths of microns and perhaps down to tens of nanometers contain just under one percent of the mass. Recombination on grains is important for the removal of gas phase ions, which are produced by cosmic rays penetrating the dark regions. Collisions of neutrals with charged grains contribute significantly to the coupling of the magnetic field to the neutral gas. Consequently, the dynamics of the grains must be included in the magnetohydrodynamic models of large scale collapse, the evolution of waves and the structures of shocks important in star formation., 17 pages, 3 figures, accepted for publication in the Journal of Plasma Physics special issue in honour of Prof. Padma K. Shukla

We discuss a novel mechanism of dust acceleration which may dominate for particles smaller than $\sim0.1~\mu$m. The acceleration is caused by their direct electrostatic interactions arising from fluctuations of grain charges. The energy source for the acceleration are the irreversible plasma processes occurring on the grain surfaces. We show that this mechanism of charge-fluctuation-induced acceleration likely affects the rate of grain coagulation and shattering of the population of small grains., Comment: 8 pages, 2 figures, revised version, submitted to Astrophysical Journal

The fundamental higher-order Landau plasma modes are known to be generally heavily damped. We show that these modes for the ion component in a weakly ionized plasma can be substantially modified by ion-neutral collisions and a dc electric field driving ion flow so that some of them can become unstable. This instability is expected to naturally occur in presheaths of gas discharges at sufficiently small pressures and thus affect sheaths and discharge structures., Comment: Published in Phys. Rev. E, see http://link.aps.org/doi/10.1103/PhysRevE.85.026412

Self‐excited dust density waves (DDWs) are studied in a striped electrode device. In addition to the usual perpendicularly (with respect to the electrode) propagating DDWs, which have been frequently observed in dusty plasma experiments on the ground, a low‐frequency oblique mode is also observed. This low‐frequency oblique DDW has a frequency much lower than the dust plasma frequency and its spontaneous excitation is observed even with a very low dust density. It is found that the low‐frequency oblique mode can exist either separately or together with the usual perpendicular mode. In the latter case, a new mode arises as a result of the interactions between the perpendicular and the oblique modes. The experiments show that these three modes satisfy the wave coupling conditions in both the frequencies and the wave‐vectors.

Complex plasma is the plasma state of soft matter which consists of weakly ionized gas (plasma) and highly charged microparticles. The microparticles are large enough to be visualized individually and their dynamics can be observed with great accuracy using simple video microscopic technique. These features allow to perform experiments with high temporal and spatial resolutions (in terms of the appropriate plasma frequency and particle separation). Furthermore, since the background gas is dilute, the particle dynamics in strongly coupled complex plasmas is virtually undamped, which provides a direct analogy to regular liquids and solids in terms of the atomistic dynamics. All these unique features allow complex plasma to be used as an ideal model system (complementary to other model systems in soft matter physics such as colloids, granular medium, etc.) to investigate various phenomena (e.g, phase transitions, phase separation, self‐organizations, linear and nonlinear waves, transport, etc.) at the most fundamental kinetic level.

The dust contamination in plasma deposition processes plays a crucial role in the quality and the yield of the products. To improve the quality and the yield of plasma processing, a favorable way is to remove the dust particles actively from the plasma reactors.Our recent experiments in the striped electrode device show that a traveling plasma modulation allows for a systematic particle removal independent of the reactor size. Besides the rf powered electrode, the striped electrode device includes a segmented electrode that consists of 100 electrically insulated narrow stripes. A traveling potential profile is produced by the modulation of the voltage signals applied on the stripes. The dust particles are trapped in the potential wells and transported with the traveling of the potential profile.The particle‐in‐cell (PIC) simulation on the potential above the segmented electrode indicates that the traveling potential profile can be realized either by applying low‐frequency (0.1–10 Hz) voltage signals with ...

In this paper we present a concise overview of our recent results concerning the electric potential distribution around a small charged particle in weakly ionized plasmas. A number of different effects which influence plasma screening properties are considered. Some consequences of the results are discussed, mostly in the context of complex (dusty) plasmas., Comment: This is a short review paper

Two sequences of Voyager 2 images of Saturn's B ring have been used to analyze the spoke phenomenon: about 100 low-resolution (220 km/lp) images of the morning and evening ansae covering a time span of 34 hr (i.e., more than three Saturn revolutions) and more than 40 high-resolution (70 km/lp) images covering about 12 hr. Positions of spoke edges have been measured for about 150 different spokes on up to 5 subsequent images each. The motion of spoke edges has been found to be close to Keplerian orbital velocity. If the observed deviation from angular velocity is interpreted as being due to the interaction of Saturn's magnetic field with charged dust particles it would result in a charge-to-mass ratio of spoke particles of q/m = −3 ± 3 C/kg. However, this deviation as well as the larger deviation observed for some trailing edges of spokes can be interpreted as being due to the phase speed at which spokes become visible or at which they disappear. Therefore the derived q/m value is only an upper limit for the true electromagnetic effect on spokes particles. An enhanced spoke activity between 120° and 150° SLS and between 300° and 330° SLS seems to be indicated in the data. The radial distribution of spoke activity follows closely the optical depth profile of the outer B ring, both being highest between the distances of 104,000 and 110,000 km. The age distribution of spokes shows a deficiency of young ages (

We have considered the evolution of dust orbits in a gravitational and electromagnetic field like that in the magnetosphere of Saturn. The orbits evolve due to the action of plasma drag and gyrophase drag (Lorentz force combined with a delay in charging of the dust). We calculate the average relative change in the semimajor axis, 〈 a dot /a 0 〉 , and the average change in eccentricity, 〈 e dot 〉 , for different initial orbits and different plasma conditions, including cases with constant temperature and density and cases with gradients in temperature and density. Finally, we adopted a plasma model which may be appropriate for the E-ring plasma of today. This model has a cold and hot electron component and the production of secondary electrons is important, contrary to the other cases considered. It appears possible that the E-ring dust particles, if injected by Encleadus at low eccentricities, will keep their low eccentricities in today's plasma environment. This would imply that the orbits would drift slowly outward mainly due to plasma drag. Using an extensive set of different parameters, we show that in some circumstances the perturbing forces may be strongly dependent on global or local plasma conditions and/or dust properties. This implies that even moderate environmental changes could have significant effects on the evolution of Saturn's E-ring, and emphasizes the need for better in situ measurements in order to understand this diffuse ring phenomenon.

The Galileo and Ulysses spaceprobes carry two similar dust detectors through interplanetary space from Venus to Jupiter. Impacts are reported which correspond to dust particles above a mass threshold of about 10 exp 13 g for which complete records exist. Between December 1989 and January 1992 Galileo repeatedly traversed interplanetary space between 0.7 and 2.26 AU and recorded 374 impacts. The observed impact rates ranged from 0.1 to about 3 impacts per day strongly dependent on whether the spacecraft moved toward or away from the sun. From October 1990 to January 1992 the Ulysses spacecraft had reached a distance of 5.17 AU from the sun and had recorded 72 impacts at rates between 0.1 and 0.5 per day. Inside about 2 AU the observed fluxes are compatible with a population of interplanetary dust particles moving on low to moderately eccentric and low inclination orbits. Outside this distance a dust particle population on different orbits is required in order to explain the Ulysses data.

We propose a simple method to approximately predict the freezing (fluid-solid) phase transition in systems of particles interacting via purely repulsive potentials. The method is based on the striking universality of the freezing curve for the model Yukawa and inverse-power-law interactions. This method is applied to draw an exemplary phase diagram of complex plasmas. We suggest that it can also be used to locate freezing transition in other substances with similar properties of interaction.

Simulation of a Langevin-dynamics model demonstrates emergence of critical fluctuations and anomalous grain transport which have been observed in experiments on "soft" quasi-two-dimensional dusty plasma clusters. It has been suggested that these anomalies derive from particular non-equilibrium physics, but our model does not contain such physics: the grains are confined by an external potential, interact via static Yukawa forces, and are subject to stochastic heating and dissipation from neutrals. One remarkable feature is emergence of leptokurtic probability distributions of grain displacements $\xi(\tau)$ on time-scales $\tau^{1/2}$ approaches the mean inter-grain distance $\Delta$. Others are development of humps in the distributions on multiples of $\Delta$, anomalous Hurst exponents, and transitions from leptokurtic towards Gaussian displacement distributions on time scales $\tau>\tau_{\Delta}$. The latter is a signature of intermittency, here interpreted as a transition from bursty transport associated with hopping on intermediate time scales to vortical flows on longer time scales., Comment: 12 pages, 9 figures

The interaction of two counterpropagating solitons of equal amplitudes has been studied experimentally and numerically in a monolayer strongly coupled complex plasma. Complex plasmas are microparticle suspensions in ion-electron plasmas. It was found that the solitons are delayed after the collision. Solitons with higher amplitude experience longer delays. The amplitude of the overlapping solitons during the collision was less than the sum of the initial soliton amplitudes.

Complex (dusty) plasmas consist of fine solid particles suspended in a weakly ionized gas. It is often necessary to manipulate particles in a complex plasma of a gas discharge. Popular manipulation methods include modulating the discharge parameters (e.g., discharge voltage or current), using the radiation pressure of a focused laser beam, and using an electrically biased wire or external magnetic field.

In an experiment aboard the International Space Station, performed using the PK-3 Plus instrument, a 13.56 MHz capacitively-coupled RF discharge was formed between parallel-plate electrodes. Neon gas at 0.2 Torr was partially ionized by applying 40 Volt peak-to-peak RF potentials to the symmetrically-driven electrodes. A mechanical shaker introduced 6.8-micron diameter polymer microspheres, or dust, into the plasma. The microspheres became highly charged. In this way a dusty plasma (also known as a complex plasma) was formed. Using video cameras and illumination by a sheet of laser light, the suspension of microparticles was imaged in situ.

Summary form only given. Laboratory complex (dusty) plasmas are low-pressure gas- discharge plasmas containing monodisperse microparticles that are highly charged due to absorption of ambient electrons and ions. The unique feature distinguishing complex plasmas is that one can vary the strength of the electrostatic coupling between particles over an extremely broad range. This allows us to explore the entire hierarchy of the phase states - ranging from gaseous to solid - and thus study all relevant generic processes occurring in strongly coupled media at the most fundamental kinetic level. Recently, the experimental discovery of "electrorheological" complex plasmas has been reported1. In such plasmas the interaction between microparticles can be controlled by external AC electric fields, due to distortion of the Debye spheres that surround microparticles. We show that interactions in electrorheological complex plasmas are equivalent to those in conventional dipolar fluids. Results of the recent microgravity experiments and complementary molecular dynamics simulations reveal variety of phase transitions controlled by the amplitude of the field, resulting in different anisotropic ("string-like") solid structures. We also report on a comprehensive thermodynamic study of anisotropic complex plasmas (with a spherically-symmetric repulsive Yukawa interaction and additional dipole-dipole interaction) induced by an external field. We propose a simple variational approach based on the Bogoliubov inequality for determining equilibrium solid phases. We show that the phase diagram of such complex plasmas exhibits numerous solid-solid phase transitions precisely controlled by the magnitude of the applied field.