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PK-4 is an experiment designed to investigate complex plasmas in a combined dc/RF discharge under microgravity conditions on board of the International Space Station. The dc discharge is produced in a glass tube with a length of 35 cm and a diameter of 3 cm. In addition, an RF discharge can be applied by external RF coils. The setup is especially suited for studying the liquid phase of the complex plasmas, e.g., flow phenomena such as turbulence or nozzles, and forces acting on the microparticles. Experiments in the laboratory and in parabolic flights have been used to determine the charge of the microparticles as well as the ion drag force acting on them. Index Terms--Complex plasmas, dc/rf discharge, fluid simulation.

The hydrodynamic response of thin plane targets to the action of the high-power proton beam of the Karlsruhe Light Ion Facility KALIF has been investigated using time-resolved one.dimensional (1-D) and two-dimensional (2-D) laser Doppler velocimetry with subnanosecond temporal resolution. A new method for shock compressibility (Hugoniot) measurements with micrometer-thick impactors and transparent barriers has been used. Experimental velocity histories have been compared to numerical simulations accounting for thermal conductivity, equation of state, and stopping power of dense strongly coupled plasma. Index Terms - Ablation plasma, computer simulation, equation of state, high-power ion beams, shockwaves.

Our present study concerns the influence of the picosecond rise-time-pulsed electromagnetic field, and the impact of nanosecond pulsed pressure on the aggregation state of horseradish peroxidase (HRP) as a model enzyme. The influence of a 640 kV/m pulsed electromagnetic field with a pulse rise-time of ~200 ps on the activity and aggregation state of an enzyme is studied by the single-molecule atomic force microscopy (AFM) method. The influence of such a field is shown to lead to aggregation of the protein and to a decrease in its enzymatic activity. Moreover, the effect of a shock wave with a pressure front rise-time of 80 ns on the increase in the HRP aggregation is demonstrated. The results obtained herein can be of use in modeling the impact of electromagnetic and pressure pulses on enzymes and on whole living organisms. Our results are also important for taking into account the effect of pulsed fields on the body in the development of drugs, therapeutic procedures, and novel highly sensitive medical diagnosticums. [ABSTRACT FROM AUTHOR]

Using the Ornstein–Zernike integral fluid equation for multi-component plasma, the dielectric properties and thermodynamical stability of dusty plasmas are studied. For the most non-ideal dust plasma subsystem, a transition to the one-component approximation is carried out. It is shown that the effective pseudopotential for determining the correlation functions in the selected subsystem should not include the contribution of this subsystem to the screening constant but also take into account the condition of total plasma quasineutrality. It is demonstrated that when the coupling parameter of the dust subsystem is smaller than unity, Γ00 < 1, the interaction potential between the charged plasma particles is fairly well described by the Debye potential with a full screening constant. For Γ00 > 1, the static dielectric function in the long wavelength domain becomes negative, and this domain expands when Γ00 increases. This leads to the appearance of attraction of particles with charges of the same sign and repulsion of particles with charges of the opposite sign. In this case, both the total pressure and the isothermal compressibility in the entire studied range of the coupling parameter Γ00 < 250 remain positive, but the isothermal compressibility of the dust subsystem becomes negative at Γ00 ≈ 2 within the studied range of variation of the plasma parameters. The sign of the derivative of the chemical potential with respect to the total number of dust particles, the positiveness of which is the third condition for the thermodynamic stability, is shown to coincide with the sign of the isothermal compressibility of the dust subsystem. Therefore, it is concluded that the equilibrium dusty plasma at Γ00 > 2 is thermodynamically unstable. [ABSTRACT FROM AUTHOR]

We irradiated the soft x-ray laser (SXRL) pulses having a wavelength of 13.9 nm, a duration time of 7 ps, and fluences of up to 27 mJ/cm2 to aluminum (Al) surface. After the irradiation process, the modified surface was observed with the visible microscope, the scanning electron microscope, and the atomic force microscope. The surface modifications caused by the SXRL pulses were clearly seen, and it was found that the conical structures having about 70-150 nm in diameters were formed under a single pulse shot. The conical structures were formed in the features with the average depth of about 40 nm, and this value was in accordance with the attenuation length of the SXRL beam for Al. However, those conical structures were deconstructed under the multiple pulse shots exposure. Thermomechanical modeling of SXRL laser interaction with Al surface, which explains nanostructure surface modification, was provided. [ABSTRACT FROM AUTHOR]

A study of the strongly coupled dusty plasma was carried out over a wide range of plasma pressures and temperatures. The plasma was investigated under conditions of low-pressure inductively coupled radio frequency gas discharge and under thermal plasma conditions at atmospheric pressure. The plasma was also formed from positively charged dust grains in the presence of a flux of ultraviolet photons. The results of experimental observations of ordered dust structures are reported, and the characteristic features of the dust structures and the conditions for their appearance are discussed. Index Terms--Dusty plasma, gas discharge, photoemission.

Heartbeat oscillations in complex plasmas with a broad range of fundamental frequencies are observed and studied. The experiments are performed with monodisperse microparticles of different diameters in argon as well as in neon plasmas. The oscillation frequency increases with increasing rf power and neutral gas pressure. At the lower frequencies, oscillations are strongly nonlinear. The microparticle pulsations, the variation of the electrical discharge parameters and the spatially resolved changes in the plasma glow are proven to be strongly correlated. Heartbeat oscillation dynamics is associated with global confinement modes. [ABSTRACT FROM AUTHOR]

We conducted a series of experiments to study lane formation in complex plasma, using the PK-3 Plus Laboratory in the International Space Station. In our experiments, small (driven) microparticles penetrate into a cloud of large (background) particles, revealing a strong tendency toward lane formation: When the driving force is strong enough, particles of both sorts form interpenetrating lines. Typically, the lanes exhibit a considerable anisotropic structural order accompanied by an enhancement of their (unidirectional) mobility. Laning is quantified locally in terms of the anisotropic scaling index. Using a "nematic" order parameter, the observed time-resolved lane-formation process is compared to a set of computer simulations of a binary Yukawa model with Langevin dynamics. This not only yields a best fit but also reveals a strong influence of the initial experimental conditions on the dynamics of lane formation. [ABSTRACT FROM AUTHOR]

Experiments with complex plasmas in a dc discharge using the PK-4 facility will be discussed, focusing on the formation of strings corresponding to an electrorheological fluid observed in recent parabolic flight experiments. [ABSTRACT FROM AUTHOR]

Conventional electrorheological (ER) fluids consist of suspensions of microparticles in usually nonconducting fluids with a different dielectric constant. The interparticle interaction, and hence, the rheology of ER fluids, is determined by an external electric field, which polarizes grains and thus induces additional dipole-dipole coupling. The electric field plays a role of a new degree of freedom that allows us to "tune" the interaction between particles. This makes the phase diagram of ER fluids remarkably diversified. Here, we report on the experimental investigations of "ER plasmas," where the control of the interparticle interaction by an externally applied electric field is due to distortion of the Debye spheres that surround microparticles in a plasma. Interactions in ER plasmas under weak ac fields are mathematically equivalent to those in conventional ER fluids. Microgravity experiments as well as molecular dynamics simulations show a phase transition from an isotropic to an anisotropic plasma states as the electric field is increased. The variational Gibbs--Bogoliubov approach allows us to recover the phase diagram of ER plasmas, which includes string fluids and anisotropic solid phases. [ABSTRACT FROM AUTHOR]

Experimental results on an auto-oscillatory pattern observed in a complex plasma are presented. The experiments are performed with an argon plasma, which is produced under microgravity conditions using a capacitively coupled rf discharge at low power and gas pressure. The observed intense wave activity in the complex plasma cloud correlates well with the low-frequency modulation of the discharge voltage and current and is initiated by periodic void contractions. Particle migrations forced by the waves are of long-range repulsive and attractive character. [ABSTRACT FROM AUTHOR]

A dedicated facility named High Radiation on Materials (HiRadMat) is being constructed at CERN to study the interaction of the 450 GeV protons generated by the Super Proton Synchrotron (SPS) with fixed solid targets of different materials. The main purpose of these future experiments is to study the generation and propagation of thermal shock waves in the target in order to assess the damage caused to the equipment, including collimators and absorbers, in case of an accident involving an uncontrolled release of the entire beam at a given point. Detailed numerical simulations of the beam-target interaction of several cases of interest have been carried out. In this paper we present simulations of the thermodynamic and the hydrodynamic response of a solid tungsten cylindrical target that is facially irradiated with the SPS beam with nominal parameters. These calculations have been carried out in two steps. First, the energy loss of the protons is calculated in the solid target using the FLUKA code [Fasso et al., “FLUKA: A multi-particle transport code,” Report Nos. CERN-2005-10, INFN/TC-05/11, and SLAC-R-773, 2005; Fasso et al., Conference on Computing in High Energy and Nuclear Physics, La Jolla, CA, 24–28 March 2003] and this energy loss data is used as input to a sophisticated two-dimensional hydrodynamic code, BIG2 [Fortov et al., Nucl. Sci. Eng. 123, 169 (1996)], which is based on a Godunov-type numerical scheme. The transverse intensity distribution in the beam focal spot is Gaussian. We consider three different sizes of the focal spot that are characterized by standard deviations, σ=0.088, 0.28, and 0.88 mm, respectively. This study has shown that the target is severely damaged in all the three cases and the material in the beam-heated region is transformed into warm dense matter including a strongly coupled plasma state. This new experimental facility can therefore also be used for dedicated experiments to study high energy density matter. [ABSTRACT FROM AUTHOR]

Expansion of shock-compressed zinc in isentropic release waves is investigated experimentally over the range of pressures from P ≃ 100 to 0.1 GPa and densities from ρ ≃ 1.2 ρ0 to ∼ 0.01 ρ0, where ρ0 is the normal density of the metal. Obtained data are analyzed with the use of a multiphase equation of state, which takes into account melting and evaporation effects at high temperatures and pressures. [ABSTRACT FROM AUTHOR]

Dust particle ordering is discussed in various types of low-temperature plasma, such as thermal plasmas at atmospheric pressure, dc glow discharges, UV- and radioactivity induced plasmas. The investigations of UV-induced dusty plasma were made under microgravity conditions. Experimental data are presented. Properties of ordered structures are discussed and the conditions of formation considered. [ABSTRACT FROM AUTHOR]

The detection of CA 125 protein in a solution using a silicon-on-insulator (SOI)-nanowire biosensor with n-type chip has been experimentally demonstrated. The surface of nanowires was modified by covalent immobilization of antibodies against CA 125 in order to provide the biospecificity of the target protein detection. We have demonstrated that the biosensor signal, which results from the biospecific interaction between CA 125 and the covalently immobilized antibodies, increases with the increase in the protein concentration. At that, the minimum concentration, at which the target protein was detectable with the SOI-nanowire biosensor, amounted to 1.5 × 10−16 M. [ABSTRACT FROM AUTHOR]

We measured the velocity of shock waves generated by the detonation of a high explosive in a stoichiometric (equimolar) mixture of Zn and S powders. The initial decrease in the velocity of the shock wave in a sample was then found to be followed by a remarkable increase in the velocity of shock wave propagation. This observation can be explained by the occurrence of the exothermic solid-state reaction Zn+S→ZnS in the zone of high dynamic pressure. The observed solid-state detonation represents a new type of transport phenomena in reactive media which may be expected to find important practical applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

Experiments with complex (“dusty”) plasmas in microgravity often show a particle-free region in the center of the discharge, which is the so-called “void.” The cause of this unexpected feature is assumed to be the ions streaming outward from the discharge center toward the radio-frequency electrodes and walls, dragging the microparticles with them out of the center. In several experiments onboard the International Space Station, single particles moving out of the void could be traced. The obtained trajectories reveal the distribution of the forces inside the void. [ABSTRACT FROM AUTHOR]

Ordered structures of rodlike (cylindrical) particles in dc and rf gas discharge plasmas were investigated. It was shown theoretically and observed experimentally that only two orientations (parallel and perpendicular to the external electric field) of cylindrical particles are possible and that changing the discharge parameters can result in the change of the particle orientation. [ABSTRACT FROM AUTHOR]