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New complex-plasma facility, Plasmakristall-4 (PK-4), has been recently commissioned on board the International Space Station. In complex plasmas, the subsystem of μm-sized microparticles immersed in low-pressure weakly ionized gas-discharge plasmas becomes strongly coupled due to the high (103-104 e) electric charge on the microparticle surface. The microparticle subsystem of complex plasmas is available for the observation at the kinetic level, which makes complex plasmas appropriate for particle-resolved modeling of classical condensed matter phenomena. The main purpose of PK-4 is the investigation of flowing complex plasmas. To generate plasma, PK-4 makes use of a classical dc discharge in a glass tube, whose polarity can be switched with the frequency of the order of 100 Hz. This frequency is high enough not to be felt by the relatively heavy microparticles. The duty cycle of the polarity switching can be also varied allowing to vary the drift velocity of the microparticles and (when necessary) to trap them. The facility is equipped with two videocameras and illumination laser for the microparticle imaging, kaleidoscopic plasma glow observation system and minispectrometer for plasma diagnostics and various microparticle manipulation devices (e.g., powerful manipulation laser). Scientific experiments are programmed in the form of scripts written with the help of specially developed C scripting language libraries. PK-4 is mainly operated from the ground (control center CADMOS in Toulouse, France) with the support of the space station crew. Data recorded during the experiments are later on delivered to the ground on the removable hard disk drives and distributed to participating scientists for the detailed analysis. [ABSTRACT FROM AUTHOR]

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 ±45° to the flow direction. Corresponding ellipticity of the pair correlation function g(r) or static structure factor S(k) gives the (normalized) shear rate of the flow. [ABSTRACT FROM AUTHOR]

It is shown that strong electrostatic interaction of highly charged microparticles (which is common for many laboratory experiments) can significantly modify the behavior of dust acoustic waves in a complex plasma giving rise to their transition, at large wave numbers, into a new regime similar to the dust thermal mode. Examples of the dispersion curves are calculated for realistic complex plasma parameters and a comparison with a recent experiment is presented. Excellent agreement is found between the theory and the experiment. [ABSTRACT FROM AUTHOR]

The excitation and propagation of solitary waves is studied experimentally in a two-dimensional strongly coupled dusty (complex) plasma. A single layer with ≈5000 microspheres (8 μm diam) was suspended in an argon plasma with a neutral gas pressure of 3.0 mTorr. The measured Debye shielding parameter was κ≈1.6, where κ=a/λ is the ratio of the lattice constant a to the Debye length λ. Nonlinear, planar longitudinal waves were launched by pushing all the particles in a rectangular region at the center of the crystal in the same direction using an 18 W green laser. Compressive solitary waves with density perturbations δn/n0≲0.8 and widths ≲5a were found to propagate in the forward direction at speeds exceeding the dust acoustic speed. For small amplitude solitary waves, the relations between amplitude, width, and velocity are consistent with those predicted for Korteweg–deVries solitons. Rarefactive perturbations were not observed to evolve into solitary waves. However, oscillatory shocks were seen to move in the backward direction after the laser force was removed. [ABSTRACT FROM AUTHOR]

The propagation of transverse waves in a two-dimensional particle suspension in a plasma is studied in the solid and liquid phase. The different states of the suspension are realized by raising the kinetic temperature of the dust particles with a new laser method. An additional laser beam is used to excite shear waves and the wave is observed by videomicroscopy in terms of the individual velocities of the dust particles. For recovering the spatial wave patterns the method of singular value decomposition is applied and compared with the method of spatial Fourier analysis of complex wave numbers. In the solid phase, weakly damped waves are found which follow the expected dispersion relation. In the liquid phase the existence of strongly damped waves is demonstrated. The real part of the wave number is in overall agreement with the predictions of the Quasi Localized Charge Approximation model for a two-dimensional system. The damping of the waves is discussed. [ABSTRACT FROM AUTHOR]

A method has been developed to heat and control temperature in a two-dimensional monolayer dusty plasma. A monolayer of highly charged polymer microspheres was suspended in a plasma sheath. The microspheres interacted with a Yukawa potential and formed a triangular lattice. Laser manipulation was used to apply random kicks to the particles. Two focused laser beams were moved rapidly around drawing Lissajous figures in the monolayer. The kinetic temperature of the particles increased with the laser power applied, and above a threshold a melting transition was observed. Characteristics of a thermal equilibrium of the laser-heated dusty plasma in solid and liquid states are discussed. [ABSTRACT FROM AUTHOR]

Measurements are reported for the radiation pressure and gas drag forces acting on a single melamine-formaldehyde microsphere. The radiation pressure force coefficient q, which would be unity if all incident photons were absorbed, has the value q = 0.94 ± 0.11. For argon, the Epstein gas drag force coefficient δ, which would be unity if impinging molecules underwent specular reflection, has the value δ = 1.26±0.13 as measured with our single-particle laser acceleration method, or δ= 1.44±0.19 as measured using the vertical resonance method. [ABSTRACT FROM AUTHOR]

The interaction of a focused powerful laser beam with micron-sized melamine formaldehyde (MF) particles was studied experimentally. The microspheres had a thin palladium coating on their surface and were suspended in a radio frequency argon plasma as a single layer (plasma crystal). A particle hit by the laser beam usually accelerated in the direction of the laser beam, consistent with the radiation pressure force mechanism. However, random-direction acceleration up to the speeds on the order 1 m/s was sometimes observed. Rocket-force mechanism is proposed to account for the random-direction acceleration. Similar, but much less pronounced, effect was also observed for MF particles without palladium coating. [ABSTRACT FROM AUTHOR]