Cluster model of aluminum dense vapor plasma

The chemical model of aluminum vapor plasma, that take into account the formation of neutral and charged clusters, is suggested. Caloric and thermal equations of state and composition of plasma were received using the available information about properties of metal clusters. It is shown, that aluminum vapors are clusterized with decrease of temperature and with increase of density. Pressure dependence on internal energy is calculated and comparison with experimental data is made. The important role of aluminum clusters, especially in an initial phase of the metals vapor heating, is demonstrated. It is shown, that the region of plasma clusterization in gaseous phase agree with known literature data for binodal of vapor-liquid transition from gaseous region. Suggested cluster model may be used to forecast the location of metal vapors binodal. The conductivity of aluminum vapor plasma was calculated. The satisfactory agreement with available experimental data is received.     

Substrate dependence of ion motion in femtosecond laser ablation cloud observed by planar laser-induced fluorescence

We have observed the motion of Sm⁺ ions as well as Sm atoms produced by femtosecond laser ablation of a solidified samarium solution sample on substrates by using a planar laser-induced fluorescence method. Kinetic energies of both Sm⁺ ions and Sm atoms increase as the electrical conductivity of the substrate decreases, which suggests the effect of surface charging. The kinetic energy of Sm⁺ ions is larger than that of Sm atoms for a variety of substrates due to the further electrical acceleration by the surface charge. The knowledge of ion motion will be the key information for the optimization of femtosecond laser simultaneous atomization and ionization of organic and inorganic samples on substrates.     

Simulations of anomalous ion diffusion in experimentally measured turbulent potential

The diffusion of plasma impurities in tokamak-edge-plasma turbulence is investigated numerically. The time-dependent potential governing particle motion was measured by 2D array of 8×8 Langmuir probes in edge region of CASTOR tokamak. The diffusion of particles is found to be classical in the radial direction, but it can be of an anomalous Lévy-walk type in the poloidal direction. The diffusion is found to be dependent on the ratio of particles’ mass and charge. When this ratio grows, the diffusion coefficient in radial direction grows as well, whereas poloidal diffusion coefficient drops down. Moreover, movement of particles in the time-frozen snapshot of this potential is investigated showing that also the time-independent potential is much more favorable for the particle diffusion in poloidal direction than in radial one. In the case of single ionized carbon ions the poloidal diffusion in time-independent potential transits to the Lévy-walk type for temperatures greater than 25 eV, for radial diffusion Lévy-walk was not observed even for 500 eV.     

High temperature Mars atmosphere. Part II: transport properties

Transport coefficients of equilibrium Martian atmosphere have been calculated in the second non-vanishing Chapman-Enskog approximation and compared with existing literature results. The present work improves previous calculations by considering a very detailed chemistry model of Martian atmosphere that includes 53 species and by extending the temperature range up to 50 000 K.     

Eddy diffusivity in convective hydromagnetic systems

An eigenvalue equation, for linear instability modes involving large scales in a convective hydromagnetic system, is derived in the framework of multiscale analysis. We consider a horizontal layer with electrically conducting boundaries, kept at fixed temperatures and with free surface boundary conditions for the velocity field; periodicity in horizontal directions is assumed. The steady states must be stable to short (fast) scale perturbations and possess symmetry about the vertical axis, allowing instabilities involving large (slow) scales to develop. We expand the modes and their growth rates in power series in the scale separation parameter and obtain a hierarchy of equations, which are solved numerically. Second order solvability condition yields a closed equation for the leading terms of the asymptotic expansions and respective growth rate, whose origin is in the (combined) eddy diffusivity phenomenon. For about 10% of randomly generated steady convective hydromagnetic regimes, negative eddy diffusivity is found.     

On existence of the spatial charge layers in plasma with regions of rapid growth of the ionization rate

1D quasi-static self-consistent model of nonequilibrium nitrogen and oxygen plasma with highly non-uniform spatial distribution of the electric field strength is used for analysis of the correlation of ionization rate profile and charged particles profiles. It is shown that inside a region of local increase of the ionization rate the layers with violation of quasi-neutrality can exist. This leads to the appearance of local static electric fields. Special attention is devoted to plasma resonance regions in microwave plasma. The role of negative ions is also studied.     

Methods for controlling of the laser-induced absorption in a BTO crystal by using of cw-laser radiation

The iron-atom concentration distribution as well as the gas-phase temperature was measured via laser-induced fluorescence (LIF) during iron-oxide nanoparticle synthesis in a low-pressure hydrogen/oxygen/argon flame reactor using ironpentacarbonyl (Fe(CO)₅) as precursor. Temperature measurements based on multi-line NO-LIF imaging are used to correct for temperature-dependent ground-state populations. The concentration measurement is calibrated based on line-of-sight absorption measurements. The influence of the precursor on the flame is observed at precursor concentrations larger than 70 ppm as the flame front moves closer to the burner surface with increasing Fe(CO)₅ concentration.     

Simulating 3D intense beam dynamics simulation using the moments method

The program of the 3D intense beam dynamic simulation based on the moments method is presented. The text was submitted by the authors in English.     

Electrohydrodynamic micropatterning of silver ink using near-field electrohydrodynamic jet printing with tilted-outlet nozzle

This paper introduces for the first time near-field electrohydrodynamic jet printing with tilted-outlet nozzle to obtain the fine and highly conductive patterns of silver (Ag) ink. Line widths produced by near-field electrohydrodynamic jet printing are less than 6 μm, which is approximately twenty times smaller than that of inkjet printing. Under optimized Ag ink annealing ranges 3–9 min for 30 wt% at 150°C, we observed Ag line pattern resistivities as low as 7×10⁻⁶ Ω⋅cm. Ag ink conduction mechanisms were brought to light from microstructure analysis and post-thermal-annealing examination of electrical characteristics.     

How to make sense of the jet correlations results at RHIC?

We review the di-hadron correlation results from RHIC. A consistent physical picture was constructed based on the correlation landscape in p _T , Δφ, Δη and particle species. We show that the data are consistent with competition between fragmentation of survived jets and response of the medium to quenched jets. At intermediate p _T where the medium response are important, a large fraction of trigger hadrons do not come from jet fragmentation. We argue that these hadrons can strongly influence the interpretation of the low p _T correlation data. We demonstrate this point through a simple geometrical jet absorption model simulation. The model shows that the correlation between medium response hadrons dominates the pair yield and mimics the double hump structure of the away-side Δφ distribution at low p _T . This correlation was also shown to lead to complications in interpreting the results on reaction plane dependence and three particle correlations. Finally, we briefly discuss several related experimental issues which are important for proper interpretations of the experimental data.     

Comparison of plume expansion in femtosecond laser ablation on oxidized and non-oxidized Sm surfaces

Time development of Sm⁺ and Sm ablation plume produced by the femtosecond laser irradiation has been investigated. The two-dimensional spatial profiles of Sm and Sm⁺ emitted from oxidized and non-oxidized Sm surface were visualized using a planar laser-induced fluorescence method. It was observed that the flow velocity of Sm⁺ is much faster than that of Sm plume in both surfaces. The plumes from the oxidized Sm surface show higher velocity than that from non-oxidized surface, which is originated by the small electric conductivity at the surface. Expansion property observed for Sm⁺ and Sm plume in the oxidized Sm surface ablation implies the formation of the Knundsen layer nearby the surface. Meanwhile, continuous emission of Sm indicates the large contribution of heating effect to emission process at the non-oxidized surface. We conclude that the fsLA process strongly depends on the electric property of the ablated surface and the heating effect contributes to the particle emission process on the conductive material surface.     

An electrosprayed coating process for fabricating hemispherical PMMA droplets for an optical diffuser

A modified electrospraying process is proposed for fabricating uniform microsized poly(methyl methacrylate) (PMMA) hemispherical droplets on poly(ethylene terephthalate) films for use as optical diffusers. In this process, an electrode controlled by an electric field is attached to a rotating collector, and various electric field conditions are applied to the droplets ejected from a positively charged nozzle. The distribution of small hemispherical droplets and the surface roughness resulting from this modified electrospraying process are more uniform than those achieved in the normal electrospraying process. The frequency of the field applied to the electrode is not critical to the production of stable PMMA droplets. The optical diffusivity of the PMMA film fabricated using this process is greater than that of normally fabricated film, demonstrating the feasibility of using this process to create newly designed optical diffusers.     

The formation of relativistic electromagnetic solitons in plasma Bragg gratings induced by two counter-propagating laser pulses

The generation of relativistic electromagnetic solitons in plasma with spatiotemporal density modulation is investigated. When two counter-propagating laser pulses overlap in underdense plasma, the interaction between the pulses and plasma modulates the electron and ion densities resulting in localized, stable, long-living relativistic electromagnetic solitons. They are caused by the Stimulated Raman Scattering instability. The dependence of the formation of relativistic electromagnetic solitons on the ion motion, plasma parameters, and laser parameters is studied by particle-in-cell simulations as well.     

Wigner Kirkwood ℏ-expansion of the density matrix in inhomogeneous superfluid Fermi systems

The generalized density matrix of superfluid inhomogeneous Fermi systems is expanded in powers of up to order ². This constitutes the generalisation of the Wigner Kirkwood -expansion of the density matrix of normal fluid systems to the pairing case.One of the authors (P.S.) is very grateful to D. Gogny for contributions in an early stage of this work several years back. He also acknowledges fruitful discussions with M. Centelles and X. Vinas.     

High temperature Mars atmosphere. Part I: transport cross sections

In the perspective of higher approximations of the Chapman-Enskog theory for transport property calculations, existing transport cross sections databases for interactions involving Earth atmosphere species have been updated and extended to Mars atmosphere components, proposing a phenomenological approach for the derivation of the relevant elastic collision integrals in neutral-neutral and neutral-ion interactions. Inelastic collision integrals terms, due to resonant charge exchange channels, have been considered and the asymptotic approach extended to the estimation of charge transfer cross section of multiple resonant processes. Electronic supplementary material  Supplementary Online Material     

A method for finding Lanczos coefficients with the aid of symmetries

A set of algorithms involving the Lanczos potential and certain kinematical quantities for some arbitrary space-times, obtained using timelike vector fields, is considered. It is shown that such algorithms appear most naturally in the context of the spin coefficient formalism. Furthermore, explicit solutions are derived for the new spin coefficient algorithms.     

Optical absorption in early stage low temperature laser produced plasma

We describe a new technique to measure the UV/visible absorption spectrum of the ablated material during the laser pulse. The technique utilizes the continuum emission from one laser produced plasma as a light source to measure the absorption properties of a second laser produced plasma which is formed on a semi-transparent target with an array of 40 μm holes. A 6 ns, 1064 nm laser was used to ablate a Ag target and the plasma absorption was measured in the range 450–625 nm for a laser fluence of 1 J cm⁻². The total absorption cross-section is (0.5–1.5)×10⁻¹⁷ cm² in the range 450–540 nm. By comparing the measured absorption with a calculation using the plasma spectroscopy code FLYCHK it can be concluded that, in the wavelength region examined here, the absorption is mainly due to bound-bound transitions.     

Local crystallization in an oxyfluoride glass doped with Er3+ ions using a continuous argon laser

Local crystalline formation in erbium doped oxyfluoride glass has been obtained under a cw Argon laser irradiation up to 1.8 W pumping power. By exciting at 514 nm, the emission from 800 nm and 850 nm corresponding to the ⁴S_3/2(²H_11/2)→⁴I_13/2 electronic transitions have been analyzed both inside and outside the irradiated area. The changes in the emission spectra indicate that the high power Ar laser irradiation has resulted in a localized desvitrification process. The temperature dependence of the fluorescence intensity ratio of the 800 nm and 850 nm emission bands has been used to determine the temperature of the irradiated zone. Moreover, the average lifetime of the ⁴S_3/2(²H_11/2) thermalized levels have been measured as a function of the excitation spot position. An important decrease is observed at the irradiated area. These results confirm that a localized cristalline phase has been created by the laser action.     

On the competiting role of mean-field and residual interactions in flow observables

Theoretical analyses of heavy-ion reactions are performed in the framework of the semi-classical Landau-Vlasov approach. The incident energies are investigated in the range from intermediate to low energy regimes, where transverse collective motion has been experimentally evidenced. The influence of the equation of state (E.O.S.) parameters on various collective observables is studied in relation with the action of the residual interactions. From the sensitivity to both aspects, and taking into account the experimental biases limitations, our investigation indicates that E.O.S. signatures should be more expected at energies below 100 MeV per nucleon.     

The use of linear superconducting electron accelerator for subcritical reactor driving

At the National Science Centre, Kharkiv Institute of Physics and Technology (NSC KIPT) the possibility of creating an installation with a subcritical reactor driven by an electron accelerator is examined. To obtain the maximal stream of neutrons from a neutron-producing target at a minimal density of energy emission, the electron energy should be in the range of 100–200 MeV and the size of the target should be as large as possible. Other important requirements are beam continuity with time and long-term stability of the accelerator parameters. The variants of using the superconducting linear accelerator on the basis of a TESLA accelerating structure as of subcritical reactor driver are considered. The basic design parameters and characteristics of this installation are presented. The text was submitted by the authors in English.