Dusty photoresonant plasma with coulomb collisions

We have studied the charging of dust particles in a dense photoresonant sodium plasma with electron and ion densities as high as 10¹⁶ cm^?3 produced by laser pumping of the resonance level of Na, which was a small admixture (up to 1%) in an argon buffer gas. We show that the charge of dust particles with a radius of 10 mm at maximum reaches 3 × 10⁵ electron charges and that the potential of the dust particles at a low electron bulk loss rate agrees well with the orbital motion limited (OML) model data. The behavior of the electric field near a dust particle was found to be nonmonotonic. We established that the distribution of the potential near a solitary charged dust particle agrees well with the Debye one, but the screening length proves to be much larger than even the electron Debye length; the discrepancies are largest at the afterglow stage of the photoresonant plasma, when the sodium ion with a low recombination coefficient is the main plasma ion. We determined the domain of parameters for a dense plasma where an ensemble of dust particles can crystallize.     

Non‐Ideal Dust Structures in Cryogenic Complex Plasmas

The possibility of the formation of dust structures in cryogenic environment at 4.2‐77 K was proved experimentally in the previous researches of cryogenic complex (dusty) plasma [1–5]. It was revealed from the experiments, among others, that the dust structures with high concentration of dust particles can be formed, in which interparticle distance is comparable with particle size ‐ super dense dusty plasma structures. Such structures had exotic properties such as globular (spherical) form, free boundaries, etc. In the present work new results on the experimental investigations of new phenomenon of spheroidizing ‐ process of the dust structure transition to compact globular shape at cryogenic temperatures ‐ were presented. Possible nature of such phenomenon is discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Specifications of dust-ion-acoustic shock waves affected by dust charge variation in four-component dissipative quantum plasma

ABSTRACT

Nonlinear propagation of dust-ion-acoustic shock waves in an unmagnetized, collisionless four-component quantum plasma containing electrons, positrons, ions and negatively charged dust grains affected by dust charge variations and viscosity of ions is studied using quantum hydrodynamic model. Considering dust charge variation give rise to calculating of charging currents of the plasma particles. These currents have been calculated with orbit limited motion theory and using Fermi-distribution functions or Boltzmann–Maxwell distribution depending on quantum or classical particles, respectively. The basic characteristics of quantum dust-ion-acoustic shock waves are investigated by deriving Korteweg–de Vries–Burgers equation under the reductive perturbation method. Depending on the relative values of the dispersive and dissipative coefficients, oscillatory and monotonic shock waves can propagate in the plasma model. The effect of chemical potential and density of dust particles on the shock wave’s height and thickness is investigated. In addition, the critical value of H (H_c) is calculated and it is shown that for R?>?0 compressive shock waves and for R?<?0 rarefactive ones can exist. The present study is applicable to researchers on quantum nonlinear structures in dense astrophysical objects and ultra-small micro- and nano-electronic devices.     

Possibility of weakly charged nonlinear solitary dust clouds near the continuum threshold of dust population in a quasi-neutral dusty plasma

Considering the Boltzmann response of the plasma ions and electrons and inertial dynamics of the charged dust grains, the possibility of very weak compressive soliton near the continuum limit of the dust population has been inferred. It is concluded that the behaviour of such coherent structures could be well described by the numerical analysis of the derived nonlinear classical energy integral equation for bounded solutions. These seem to be higher order dispersive structures within acoustic limit of the nonlinear turbulence. It is observed that the dust density enhancement beyond the continuum threshold causes regular increment in width and amplitude of the soliton structures. It is found that the soliton amplitude sensitively depends on the massive impurity’s population. These coherent structures could be visualized as weakly charged solitary dust clouds of finite extension (∼ plasma Debye length) within Boltzmann environment of plasma particles in their local surroundings. The seeding mechanism of such clouds may be attributed to some plasma instabilities driven by either internal or external free energy sources. Numerical analysis of the problem concludes that the experimental observations of such clouds could be possible in low density plasma regime. It is deduced that for plasma density ∼ 10⁶ cm^-3 at temperatures of a few electron volts and for micron to l0nm sized dust grains, the observation of such structures could be possible within wide range variability of the dust population density.     

Highly nonideal classical thermal plasmas: Experimental study of ordered macroparticle structures

The formation of spatially ordered CeO₂ particle structures in a thermal plasma at atmospheric pressure and temperatures of 1700–2200 K is studied. The spatial structure of the particles in the plasma is analyzed using laser time-of-flight counting of individual particles. Probe and optical diagnostics are used to determine the parameters of the thermal plasma. The CeO₂ particles were positively charged (about 10³ electronic charges). The resulting Coulomb interaction parameter for the particles is γ _p>120, which corresponds to a highly nonideal plasma. Zh. éksp. Teor. Fiz. 111, 467–477 (February 1997)     

Ordered structures in a nonideal dusty glow-discharge plasma

The formation of ordered structures of charged macroparticles in a constant-current neon glow-discharge plasma is investigated. Experiments were performed with two types of particles: thin-walled glass spheres 50–63 μm in diameter and particles of Al₂O₃, 3–5 μm in diameter. Formation of quasicrystalline structures is observed in the standing strata and in an artificially created double electric layer. The formation of extended filamentary structures of macroparticles in the absence of visible stratification of the positive column has been observed for the first time. The influence of the discharge parameters on the formation of the ordered structures and their melting is examined. The form of the interaction potential between the charged macroparticles is considered, as well as changes in the conditions for maintaining the discharge in the presence of high concentrations of dust particles. Zh. éksp. Teor. Fiz. 112, 2030–2044 (December 1997)     

Mechanism of diffusion of positively charged dust particles in a photoemission cell under microgravity conditions

The decay of a dusty plasma in a photoemission cell under microgravity conditions is investigated on the basis of the method of nonlocal moments. It is founds that plasma decay in space experiments occurs in accordance with the mechanism of free electron diffusion followed by dust particle drift. An analytic solution is found for the evolution of radial distributions of the dust particle concentration and the electric field under the experimental conditions. The effect of abnormally high temperatures of dust particles is considered. The effect of axial magnetic fields on the decay of dusty plasma is investigated. It is shown that the plasma decay in a magnetic field is governed by the ambipolar diffusion mechanism, the decay being prolonged up to 10³ s in a magnetic field on the order of 10³–10⁴ G in strength.     

Ultrahigh charging of dust particles in a nonequilibrium plasma

Charging of dust particles in a plasma with the two-temperature energy distribution of electrons has been studied. It has been shown that the dust-particle potential divided by the electron temperature decreases with increasing electron temperature in the plasma with cold ions. Owing to this behavior, the potential of the dustparticle surface increases with the electron temperature more slowly than the linear function and is lower than the electron temperature (divided by the elementary charge) for T _e > 5.5 eV in hydrogen and for T _e > 240 eV in argon. The fraction of fast electrons at which these electrons begin to contribute to the charge of dust particles has been determined. It has been shown that the charge of micron particles can reach 10⁶ elementary charges. The effect of the cold and thermal field emission on the charge of dust particles has been analyzed. The possibility of obtaining ultrahigh charges (to 10⁷ elementary charges on dust particles with a radius of 50–100 μm irradiated by a 25-keV 1-mA electron beam has been demonstrated.     

The dynamics of macroparticles in a direct current glow discharge plasma under microgravitation conditions

The dynamics of large-sized (70-180 μm) spherical bronze particles in a direct current glow discharge plasma was studied experimentally under microgravitation conditions. The temperatures, velocities, pair correlation functions, and self-diffusion coefficients of macroparticles were measured at various discharge currents. The charges of dust particles (on the order of 10⁶ e) corresponded to high surface potentials of about 30–40 V. The experimental data were in close agreement with the simulation data on Yukawa systems with weak screening of dust charges. The influence of macroparticles on equilibrium ionization in a dense dust cloud was considered.     

Pair Interaction Potential of Particles for Two‐Component Plasma

In this work the semiclassical potential for plasma particles pair interactions, which takes into account the diffraction effects due to the uncertainty principle in two‐component plasma (the region of temperatures 10⁴K < T < 10⁸K and densities 10²¹cm^–3 < n ≤ 10²⁴cm^–3), was proposed. The values of this potential were numerically calculated and an interpolation formula was obtained (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effective interaction potential and ordered structures of dust particles in a gas-discharge plasma

An effective potential is proposed for the interaction between dust particles in a gas-discharge plasma which takes account of the following physical factors: the spatial dependence of the particle charges on the floating potential of the plasma, anisotropy of the interaction, resulting from focusing of the negatively charged particles of the drift ion current, and aspects of screening of the dust particles by plasma electrons and ions which interact strongly with them and recombine faster in their vicinity and on their surface. Monte Carlo calculations explain the formation of threadlike structures of dispersed particles, and also “transverse crystallization” of these “threads” in a stratified gas-discharge plasma. Zh. éksp. Teor. Fiz. 115, 819–836 (March 1999)     

Kinetic treatment of acoustic waves in a four‐component dusty plasma

A kinetic formulation is developed to investigate low‐frequency dust ion acoustic waves (DIAWs) and dust acoustic waves (DAWs) as well as numerically for a four‐component, collisionless, unmagnetized dusty plasma, using the linearized Vlasov–Poisson model for species obeying the Maxwellian distribution. In particular, the dynamics of low‐frequency DIAWs is investigated by considering two cases. In the first case, ions and positive dust particles are assumed to be dynamically adiabatic while the negative dust particles are static in the background. In second case, the ions are taken adiabatic, while both positive and negative dust particles are static in the background. For DAWs, the ions are assumed to be isothermal, while both positive and negative dust species are considered adiabatic. Electrons are assumed to be isothermal in all cases. The linear characteristics and Landau damping rates for DIAWs and DAWs are investigated with effects of the dust particle concentrations and different temperature ratios. It is noted that for higher values of positive dust concentration, DIAWs (DAWs) are less (more) damped. It is also observed that the damping rate increases (decreases) as T_i approaches T_e for DIAWs (DAWs). It is worth adding here that the theoretical results presented here are supported by numerical analyses and illustrations. The relevance of the study to laboratory and cosmic plasmas is also pointed out.     

Impacts of fast meteoroids and a plasma–dust cloud over the lunar surface

The possibility of the formation of a plasma–dust cloud in the exosphere of the Moon owing to impacts of meteoroids on the lunar surface is discussed. Attention is focused on dust particles at large altitudes of ~10–100 km at which measurements were performed within the NASA LADEE mission. It has been shown that a melted material ejected from the lunar surface owing to the impacts of meteoroids plays an important role in the formation of the plasma–dust cloud. Drops of the melted material acquire velocities in the range between the first and second cosmic velocities for the Moon and can undergo finite motion around it. Rising over the lunar surface, liquid drops are solidified and acquire electric charges, in particular, owing to their interaction with electrons and ions of the solar wind, as well as with solar radiation. It has been shown that the number density of dust particles in the plasma–dust cloud present in the exosphere of the Moon is ?10^?8 cm^?3, which is in agreement with the LADEE measurements.     

The diffusion of macroparticles and criteria of phase transitions for dust structures in weakly ionized plasma

The dynamics of charged particles is investigated under conditions close to those of experiments in a weakly ionized laboratory gas-discharge dust plasma. The existing phenomenological criteria of phase transitions for dust structures in such a plasma are treated, and new criteria are suggested. The parameters responsible for the order and scaling of dynamic processes in Yukawa dissipative systems are determined. The relation for the diffusion coefficient D of macroparticles in strongly correlated liquid structures is derived.     

Scattering processes and electrical conductivity of partially ionized hydrogen plasma

We consider partially ionized hydrogen plasma for the density region n_e = (10¹⁸ ÷ 10²²) cm^—3. The cross sections for scattering processes between the particles are calculated within the partial wave method. Charged particles in the system (electrons, protons) interact via an effective potential that takes into account threeparticle correlations. The Buckingham polarization potential is used to describe electron‐atom and proton‐atom interactions. The electrical conductivity is determined using the Chapman‐Enskog method. The results are compared with other available data.     

Study of star extinction beyond comet P/Halley

Summary By studying star extinction behind comet P/Halley caused by dust grains, it is possible to identify structures in the dust environment when the extinction does not follow ther ⁻² profile with radial distance from the nucleus. This has been done with CCD images taken from Catania Observatory on April 23, 1986. The result of the study confirms the presence of two dust jets seen also with images taken with narrow band (cont 685 nm) filters looking only at solar light reflected by dust particles. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Charge and structures of dust particles in a gas discharge at cryogenic temperatures

A dusty plasma in a dc gas discharge is considered at low (cryogenic) temperatures of the gas. The formation of dusty plasma structures consisting of monodisperse poly(styrene) particles (d = 5.44 μm) in a dc glow discharge is experimentally investigated at cryogenic temperatures in the range from 4.2 to 77 K, and the results obtained are presented. The ion velocity distribution function and the charging of dust particles at cryogenic temperatures are calculated using the molecular dynamics method. The primary attention is focused on the correct inclusion of ion-atom collisions in the analysis. This is essential to the understanding of the main mechanisms of the experimentally observed increase in the density of dust particles with decreasing temperature of the gas in the discharge.     

电磁脉冲在实验室等离子体中传播时间的实验研究

利用矢量网络分析仪，对频域9—11 GHz的电磁脉冲在实验室稳态无磁场等离子体中传播时间的问题进行了实验研究.实验发现当等离子体密度在0.65—1.43×10¹¹ cm^-3范围内时，电磁脉冲通过该等离子体传播的时间将会小于该电磁脉冲在真空中传播同样距离所需要的时间，在密度约为1.10×10¹¹ cm^-3时，这两个时间差会出现一个极值.进一步的研究表明在此密度范围内，非磁化Xe等离子体中的电磁波色散关系将不再成立. 关键词： 电磁脉冲 脉冲传播时间 等离子体密度 色散关系     

Small amplitude dust-acoustic soliton energy in dusty plasmas with suprathermal polarization force

The effect of suprathermal polarization force on both linear and weakly nonlinear dust-acoustic solitary structures in a three-component dusty plasma is investigated. For this purpose, a new expression of the polarization force acting on dust particles that include the electronic suprathermal effect is derived. The results are applied to two different experimental dusty plasmas. We have found that the polarization force acting on the dust grains decreases as the electron suprathermality becomes more significant. In addition, we have shown that, for a given value of the spectral index κ , the polarization force magnitude fluctuates from one plasma to another. The changes arising in the propagation of small-amplitude dust-acoustic (DA) solitons due to the presence of this suprathermal polarization force are also analysed. Interestingly, an increase in the magnitude of the polarization force leads to an increase in the amplitude and width of DA soliton and provides more energy to the motion of this soliton.     

Die Verteilung der natürlichen Radioaktivität auf das Größenspektrum des natürlichen Aerosols

The apparatus described allows to measure the distribution of natural radioactivity on aerosol particles. Careful measures were taken that the aerosol concentration and its size spectrum were not altered before being examined. To increase the accuracy of the measurements the natural aerosol was charged with thoron decay products. The resulting electric charge-distribution by ion diffusion on dust particles is known, therefore the radii of these particles could be calculated by mobility measurements. By means of the law, governing attachment of emanation decay products on dust particles — as derived byLassen orWieser andStierstadt (afterBricard), it is possible to calculate the size spectrum of natural aerosol from the measured activity spectrum. Until now we have onlyion spectra for the range of size 6×10^?7 to 10^?5 cm. With the quoted apparatus however it is possible to measure thesize spectrum of natural aerosol. So we have a simple size-spectrometer, that covers a large range of particles. Among other things can be deduced from these measurements, that the natural radioactivity of air is attached to particles of radii from 10^?6 up to 10^?5cm, — the main part of the activity being carried by aerosols with radii between 4 and 6×10^?6cm. From the calculated aerosol spectrum (r from 6×10^?7 to 10^?5 cm) follows a mean particle radius ofr=2,5×10^?6cm at a particle concentration of 3×10⁴cm^?3.