Search

Aiming to delineate the physical framework of blazars, we present an effective method to estimate four important parameters based on the idea proposed by Becker & Kafatos, including the upper limit of central black hole mass M, the Doppler factor δ, the distance along the axis to the site of the Îł -ray production d (which then can be transformed into the location of Îł -ray-emitting region R Îł ) and the propagation angle with respect to the axis of the accretion disk Φ. To do so, we adopt an identical sample with 809 Fermi-LAT-detected blazars which had been compiled in Pei et al. These four derived parameters stepping onto the stage may shed new light on our knowledge regarding Îł -ray blazars. With regard to the paper of Becker & Kafatos, we obtain several new perspectives, mainly in (1) putting forward an updated demarcation between BL Lacs and FSRQs based on the relation between broad-line region luminosity and disk luminosity both measured in Eddington units, i.e., L disk/ L Edd = 4.68 Ă— 10âˆ'3, indicating that there are some differences between BL Lacs and FSRQs on the accretion power in the disk; (2) proposing that there is a so-called “appareling zone,” a potential transition field between BL Lacs and FSRQs where the changing-look blazars perhaps reside; (3) the location of Îł -ray emission region is principally constrained outside the broad-line region, and for some BL Lacs are also away from the dusty molecular torus, which means the importance of emission components in the jet. [ABSTRACT FROM AUTHOR]

Plasma is an ionized gas that responses collectively to any external (or internal) perturbation. Introducing micron-sized solid dust particles into plasma makes it more interesting. The dust particles acquire large negative charges on their surface in low-temperature laboratory plasma and exhibit collective behavior similar to the ambient plasma medium. Some remarkable features of the charged dust grain medium (dusty plasma) allow us to use it as a model system to understand a number of physics phenomena at a microscopic level. In this perspective paper, the author highlights the role of dusty plasma experiments as a learning tool for undergraduate and post-graduate physics students at higher academic institutions. Students could have great opportunities to understand basic physical phenomena as well as learn about many advanced data analysis tools and techniques by performing dusty plasma (plasma) experiments. A few simple experiments in a single dusty plasma device that connect the basic physics phenomena are discussed. [ABSTRACT FROM AUTHOR]

The creation of a spatially extended stable DC complex plasma crystal is a big experimental challenge and a topical area of research in the field of dusty plasmas. In this paper we describe a newly built and commissioned dusty plasma experimental (DPEx-II) device at the Institute for Plasma Research. The device can support the formation of large sized Coulomb crystals in a DC glow discharge plasma. The plasma in this L-shaped table-top glass chamber is produced between a circular anode and a long tray shaped cathode. It is characterized with the help of various electrostatic probes over a range of discharge conditions. The dust particles are introduced by a dust dispenser to form a strongly coupled Coulomb crystal in the cathode sheath region. The unique asymmetric electrode configuration minimizes the heating of dust particles and facilitates the formation of crystalline structures with a maximum achievable dimension of 40 cm × 15 cm using this device. A larger crystal has numerous advantages over smaller ones, such as higher structural homogeneity, fewer defects, lower statistical errors due to finite size effects etc. A host of diagnostics tools are provided to characterize the Coulomb crystal. Results of a few initial experiments aimed at demonstrating the technical capabilities of the device and its potential for future dusty plasma research, are reported. [ABSTRACT FROM AUTHOR]

This paper presents recent progress on the development of the new multi-purpose particle modeling and simulation tool VizGrain. A unique aspect of VizGrain is that it allows computational modeling of particle dynamics in a variety of systems, including rarefied gas dynamics, macroscopic particle dynamics (e.g., dust particles, droplets, etc), particle-in-cell modeling, and hybrid continuum-particle modeling within a single integrated framework. VizGrain allows working with atomic sized particles and particles with finite macroscopic sizes. The former approach is used to model rarefied gas dynamics and conventional non-equilibrium plasmas, while the finite sized macro-particles are considered for the modeling of dusty plasmas, aerosols, droplets etc. In this latter case, the electrical charge up of particles in a plasma environment is considered. The model features a comprehensive variety of drag forces that can act on both atomic and macro-particles. A detailed description of the physical models implemented within VizGrain is presented, to provide insights into the approach that can be taken in other particle-based codes in the community. These models are scrupulously validated against the benchmark problems proposed in the research literature for a variety of applications from the plasma reactors used in semiconductor industry to high-speed rarefied gas dynamics problems. [ABSTRACT FROM AUTHOR]

In this paper, the formation of the electron energy distribution function (EEDF) in the argon dusty plasma of the positive column of glow discharge at low pressure is investigated. A model for calculating EEDF in the local approximation is adapted to find the nonlocal EEDF via the Holstein–Tsendin model. The results show that, contrary to the prevalent opinion in the literature, the presence of dust has little effect on the EEDF up to the limiting values of the density of dust particles that can be injected into the plasma for the considered conditions. It is also shown that, when obtaining the nonlocal EEDF, the spatial profiles of the axial (heating) and radial (ambipolar) fields should be chosen from a self-consistent solution. Additionally, the differences between the local and nonlocal EEDFs increase in the peripheral regions of the discharge due to a sharp decrease of fast electrons in the nonlocal case. Significant changes in the form of the nonlocal EEDF along the radius also lead to noticeable changes in other characteristics of the electrons in this area, especially for those with a large energy threshold (e.g. due to excitation, ionization). [ABSTRACT FROM AUTHOR]

Particle contamination due to plasma processing motivates the design of a method of electrically lifting particles in a time interval after a plasma's power is turned off. Small solid dust particles have electric charges that are not frozen until a late stage of the plasma afterglow. Beyond that time, before they fall to a surface below and cause defects, particles can be lifted in a controlled manner by applying an appropriate direct-current (DC) electric field, as we demonstrate experimentally. A few milliseconds after an argon plasma's capacitively coupled radio-frequency power is switched off, a vertical DC electric field is applied. Thereafter, video imaging shows that the falling of the particles is slowed or stopped altogether, depending on the magnitude of the upward electric force. [ABSTRACT FROM AUTHOR]

The last decade has seen the development of new experimental devices to explore the physics of magnetized dusty plasmas. Because of the small charge-to-mass ratio of the charged microparticles, it is necessary to operate these experiments at high magnetic fields of several Tesla in order to observe the direct effect of the magnetic forces on the transport properties of the charged microparticles. While the study of magnetized dusty plasmas is still the ultimate goal, these experiments have also provided new opportunities to studies regimes of strongly magnetized, low temperature, laboratory plasmas that have not been extensively explored. Experiments show the formation of new types of self- and imposed-ordered structures that form in both the plasma and among the microparticles. This paper summarizes recent experimental observations of plasma filamentation (in the plasma) and will discuss possible connections to 'dust gridding' phenomena that are observed in the magnetized dusty plasma experiment device. [ABSTRACT FROM AUTHOR]

In this paper, we report the first experimental observation of internal resonance in a dusty plasma, which shows the intrinsic nonlinearities of dust interactions in plasmas. When driving a system of vertically aligned dust particle pairs in the vertical direction, the horizontal motion is found to be excited during onset of internal resonance when the higher-frequency horizontal sloshing mode is nonlinearly coupled to the vertical breathing mode through the 1:2 commensurable relation. A theoretical model of the nonlinear interaction of dust particles in plasma is also provided and the results of the theoretical model are shown to match experimental observations. [ABSTRACT FROM AUTHOR]

The theoretical description of complex (dusty) plasmas requires multiscale concepts that adequately incorporate the correlated interplay of streaming electrons and ions, neutrals and dust grains. Knowing the effective dust-dust interaction, the multiscale problem can be effectively reduced to a one-component plasma model of the dust subsystem. The goal of this paper is a systematic evaluation of the electrostatic potential distribution around a dust grain in the presence of a streaming plasma environment by means of two complementary approaches: (i) a high-precision computation of the dynamically screened Coulomb potential from the dynamic dielectric function and (ii) full 3D particle-in-cell simulations, which self-consistently include dynamical grain charging and nonlinear effects. The range of applicability of these two approaches is addressed. [ABSTRACT FROM AUTHOR]

In this paper, a charged multi-walled carbon nanotube (MWCNT), which is surrounded by charged nanoparticles, is modeled as a cylindrical shell of electron{ion{dust plasma. By employing classical electrodynamics formulations and the linearized hydrodynamic model, the dispersion relation of the dust acoustic wave oscillations in the composed system is investigated. We obtain a new low-frequency electrostatic excitation in the MWCNT, i.e. dust acoustic wave oscillations. [ABSTRACT FROM AUTHOR]

This paper investigates the propagation of linear dust acoustic waves in inhomogeneous dusty plasmas due to spatial gradients of dust charge, plasma densities. A linear dispersion relation is obtained with the non-adiabatic dust charge fluctuation and the non-thermally distributed ions. The numerical results show that the inhomogeneity, non-thermal ions and non-adiabatic dust charge fluctuation have strong influence on the frequency and the damping rate of waves. [ABSTRACT FROM AUTHOR]

Considering the transverse perturbation and axially non-planar geometry, the cylindrical Kadomtsev-Petviashvili (KP) equation is investigated in this paper, which can describe the propagation of dust-acoustic waves in the dusty plasma with two-temperature ions. Through imposing the decomposition method, such a (2+1)-dimensional equation is decomposed into two variable-coefficient (1+1)-dimensional integrable equations of the same hierarchy. Furthermore, three kinds of Darboux transformations (DTs) for these two (1+1)-dimensional equations are constructed. Via the three DTs obtained, the multi-soliton-like solutions of the cylindrical KP equation are explicitly presented. Especially, the one- and two-parabola-soliton solutions are discussed by several figures and some effects resulting from the physical parameters in the dusty plasma and transverse perturbation are also shown. [ABSTRACT FROM AUTHOR]

A method is demonstrated for controlling the charge of a dust particle in a plasma afterglow, allowing a wider range of outcomes than an earlier method. As in the earlier method, the dust particles are located near an electrode that has a DC voltage during the afterglow. Here, that DC voltage is switched to a positive value at a specified delay time, instead of maintaining a constant negative voltage as in the earlier method. Adjusting the timing of this switching allows one to control the residual charge gradually over a wide range that includes both negative and positive values of charge. For comparison, only positive residual charges were attained in the earlier method. We were able to adjust the residual charge from about −2000 e to +10 000 e, for our experimental parameters (8.35 µ m particles, 8 mTorr argon pressure, and a DC voltage that was switched from −150 V to +125 V within the first two milliseconds of the afterglow). The plasma conditions near the dust particles changed from ion-rich to electron-rich, when the electrode was switched from cathodic to anodic. Making this change at a specified time, as the electrons and ions decay in the afterglow, provides this control capability. These results also give insight into the time development of a dust particle's charge in the afterglow, on a sub-millisecond time scale. [ABSTRACT FROM AUTHOR]

The advent of high-angular-resolution IR and submillimeter interferometry allows for spatially resolved observations of the parsec-scale environment of active galactic nuclei (AGNs), commonly referred to as the “torus.” While molecular lines show the presence of large, massive disks, the IR observations appear to be dominated by a strong polar component that has been interpreted as a dusty wind. This paper aims at using characteristics shared by AGNs in each of the wavebands and a set of simple physical principles to form a unifying view of these seemingly contradictory observations: dusty molecular gas flows in from galactic scales of ∼100 pc to the subparsec environment via a disk with small to moderate scale height. The hot, inner part of the disk puffs up due to IR radiation pressure and unbinds a large amount of the inflowing gas from the black hole’s gravitational potential, providing the conditions to launch a wind driven by the radiation pressure from the AGN. The dusty wind feeds back mass into the galaxy at a rate of the order of ∼0.1–100 M⊙ yr−1, depending on the AGN luminosity and Eddington ratio. Angle-dependent obscuration as required by AGN unification is provided by a combination of disk, wind, and wind-launching region. [ABSTRACT FROM AUTHOR]

Frequent observations of ion beams moving out from Saturn’s plasma environment hints at the generation of ion Bernsteinâ€"Greeneâ€"Kruskal (BGK) modes. As the plasma environments of Saturn and its moon Enceladus are characterized by the ubiquitous presence of massive negatively charged dust particles, the existing BGK theory for electron-ion plasma models cannot address this scenario. This manuscript develops a theoretical model for studying ion BGK modes in dusty plasmas. The analysis reveals that the presence of dust in the plasma enhances the stability of BGK modes. As the dust density increases, the effect of other parameters on stability, such as the electron temperature, becomes negligible. The model is developed by assuming that electrons and ions follow a kappa distribution, featuring a long tail trend in the superthermal component, in agreement with observations. Different scenarios with either electrons or ions obeying a Maxwell or kappa distribution function have been considered. A thorough analysis of the trapped ion distribution function considering various combinations indicates that a plasma where electrons are in thermal equilibrium and ions follow kappa distribution is the least favorable system for the generation of BGK modes. [ABSTRACT FROM AUTHOR]

By employing the quantum hydrodynamic model for electron-ion-dust plasma, we derive a dispersion relation of the quantum dusty plasma. The effects of the dust size distribution on the dispersion relation in a cold quantum dusty plasma are studied. Both analytical and numerical results are given to compare the differences between the dusty plasma by considering the dust size distribution and the mono-sized dusty plasma. It is shown that many system parameters can significantly influence the dispersion relation of the quantum dusty plasma. [ABSTRACT FROM AUTHOR]

If a particle in an anisotropic plasma is replaced by a charge q0and a dipole p0, without modifying the moment of the monopole and the dipole, the approximation method neglecting higher-order terms is not sufficient for describing the actual potential distribution around the particle. By introducing the concepts of the 'apparent' charge qand the 'apparent' dipole pin this paper, the surface potential of the particle caused by q0+ p0and the sheath charge+dipole can be decided by q+ p. If we assume that the dusty plasma has roughly equal moments of particle dipoles (+) and sheath dipoles (?), i.e. 'momentneutrality', besides the electroneutrality relation, the relationship between the actual moment and the 'apparent' moment can be acquired, and the potential around the particle can be calculated self-consistently. Based on the physical model, the electrostatic force on an isolated particle in an anisotropic plasma may be calculated and the pair interaction potential energy between particles or the coupling parameter can be acquired even for high ?avalues. Compared with other methods, the system is solvable analytically and thus yields clear insight into its physical behaviour. [ABSTRACT FROM AUTHOR]

When a three-dimensional dust cloud is present in a plasma, a dustfree region, called a void, is usually obtained in the plasma centre. Under certain conditions, this region exhibits a self-excited unstable behaviour consisting of successive contractions and expansions of its size. In this paper, this low frequency instability (few Hz), called a 'heartbeat', is characterised by various diagnostics. Electrical and optical measurements both correlated with high speed imaging brought to the fore the main features of this instability. Forces involved in the void existence are an inward electrostatic force and an outward ion drag one. The force balance ensures an open void but this equilibrium can be disturbed, leading to the observed instabilities. As these forces are strongly dependent on local ionisation conditions, correlations between physical processes in the plasma volume and the dust cloud motion are investigated through experimental results. [ABSTRACT FROM AUTHOR]

The interaction of a small object with surrounding plasma is an area of plasma-physics research with a multitude of applications. This paper introduces the plasma octree code pot, a microscopic simulator of a spheroidal dust grain in a plasma. pot uses the Barnes–Hut treecode algorithm to perform N-body simulations of electrons and ions in the vicinity of a chargeable spheroid, employing also the Boris particle-motion integrator and Hutchinson’s reinjection algorithm from SCEPTIC; a description of the implementation of all three algorithms is provided. We present results from pot simulations of the charging of spheres in magnetised plasmas, and of spheroids in unmagnetized plasmas. The results call into question the validity of using the Boltzmann relation in hybrid PIC codes. [ABSTRACT FROM AUTHOR]

Atmospheric pressure low-temperature plasmas are often utilized to perform particle synthesis, treatment, and removal. It is well-known that dust particles are highly negatively charged in these plasmas; however, little is known about dust particle charging behavior as particles leave the plasma volume and pass through the spatial afterglow region. In this work, monodisperse particles of various sizes and work functions were introduced into an atmospheric pressure radiofrequency capacitively coupled flow-through plasma. Dust particle electrical mobility distributions downstream of the flow-through plasma were measured utilizing a differential mobility analyzer in conjunction with a condensation particle counter at various gas flow velocities. Charge distributions were determined from the measured electrical mobility distributions. Experiments confirm that particles become less negatively charged, and even net-positively charged after leaving the plasma volume, with a distribution that follows a shifted Boltzmann charge distribution. Additionally, particle charge in the effluent of the flow-through plasma is negligibly dependent on work function but highly size and flow velocity dependent. Larger particles were shown to have a higher magnitude of charge under all studied conditions; however, particle polarity was switchable by varying gas flow velocity. The charging dynamics were simulated utilizing a constant number Monte Carlo model that accounts for electron temperature decay and the transition from ambipolar to free diffusion of electrons and ions in the spatial afterglow. Simulation results also suggest that, at the same flow velocity, larger particles obtain a greater magnitude of charge, negative or positive. The decrease in electron mobility and the difference between ion and electron convective loss rates create an ion-rich region in the plasma effluent that promotes ion–particle collisions and drives particle charge removal and even reversal of polarity. Larger particles more favorably collide with energetic species in these environments, which results in higher charge states. [ABSTRACT FROM AUTHOR]

The COVID-19, viral influenza, tuberculosis, and other widespread infectious diseases evidence that pathogenic biological aerosols (PBAs) are a serious threat to public health. Different from traditional inactivation methods, such as ultraviolet (UV) light which are only safe to use when people are not present, and high-efficiency particulate filters (HEPA) which merely filter microbes without killing them, atmospheric pressure nonequilibrium plasma (APNP) has shown its tremendous potential in drastically diminishing the aerosol transmission route of the infectious agents through the abatement of PBAs. The key issues to develop high performance APNP based air purification system are critically reviewed. Systematic studies on the hazards of different PBAs and the spread of PBAs in indoor environments guide the development of APNP sources to control communicable diseases. The key six sampling and seven detection methods on PBAs are introduced to analyze the PBA abatement efficiency by APNP. Seven common APNP sources which can remove viruses and bacteria aerosols efficiently developed during the past 8 years are introduced. For the APNP sources with small plasma volume, the electric field and diffusion driven charging are the dominant mechanisms to charge PBAs, while the common methods of dusty plasma research can be adapted to atmospheric-pressure conditions to describe the charging effects of APNP sources with large plasma volume. Plentiful long- and short-lifetime reactive oxygen and nitrogen species (RONS) generated by APNP effectively contribute to inactivation of bacterial aerosols. Current studies suggest that viral aerosols are mainly inactivated by short-lifetime RONS including 1O2, ONOO− and ONOOH. The study on the dissolution and reaction of gaseous RONS in microdroplets and accurate measurements on the evolution of charged PBAs are envisaged to be the focus of future research. Opportunities for multidisciplinary collaborative research to advance the development of next-generation high-performance plasma-based air purifiers are highlighted. [ABSTRACT FROM AUTHOR]

This paper reports on the laser heating of nanoparticles (diameters μm) confined in a reactive plasma by short (150 ps) and intense ( mJ) UV (355 nm) laser pulses (laser-induced incandescence, LII). Important parameters such as the particle temperature and radius follow from analysis of the emission spectrum of the heated nanoparticles. The nanoparticles are not ideal black bodies, which is taken into account by calculating their emissivity using a light-scattering theory relevant to our conditions (Mie theory). Three sets of refractive index data from the literature serve as model input. The obtained radii range between 100 and 165 nm, depending on the choice of refractive index data set. By fitting the temperature decay of the particles to a heat exchange model, the product of their mass density and specific heat is determined as J K−1 cm−3, which is considerably smaller than the value for bulk graphite at the temperature our particles attain (3000 K): 4.8 J K−1 cm−3. The particle sizes obtained in situ with LII are compared with ex situ scanning electron microscopy analysis of collected particles. Quantitative assessment of the LII measurements is hampered by transport of particles in the plasma volume and the fact that LII probes locally, whereas the samples with collected particles have a more global character. [ABSTRACT FROM AUTHOR]

The Parker Solar Probe (PSP) aims to explore the nascent solar wind close to the Sun. Meanwhile, PSP is also expected to encounter small objects like comets and asteroids. In this work, we survey the ephemerides to find the chance of a recent encounter and then model the interaction between released dusty plasmas and solar wind plasmas. On 2019 September 2, a comet-like object, the 322P/Solar and Heliosphere Observatory, just passed its perihelion flying to a heliocentric distance of 0.12 au and swept by PSP at a relative distance as close as 0.025 au. We present the dynamics of the dust particles released from 322P, forming a curved dust tail. Along the path of PSP in the simulated inner heliosphere, the states of plasma and magnetic field are sampled and illustrated, with the magnetic field sequences from simulation results being compared directly with the in situ measurements from PSP. Through the comparison, we suggest that 322P might be at a deficient activity level releasing limited dusty plasmas on its way to becoming a "rock comet." We also present images of solar wind streamers as recorded by the Wide-field Imager for Solar Probe Plus, showing an indication of dust bombardment for the images superposed with messy trails. We observe from the Large Angle and Spectrometric Coronagraph that 322P was transiting from a dimming region to a relatively bright streamer during its perihelion passage, and perform a simulation to confirm that 322P was flying from relatively faster to slower solar wind streams, modifying the local plasma states of the streams. [ABSTRACT FROM AUTHOR]

We present an electrostatic particle extractor system (EPEX) which extracts particles from a reactive, particle-growing plasma by using the electrostatic force. The system is able to extract eight samples during a single growth cycle without the need to interrupt the plasma process. Using video microscopy, imaging-Mie, and Mie polarimetry we demonstrate the minimal invasiveness of EPEX. The extraction voltage and its duration are optimized to tune the particle density on the sample wafer. Compared to other invasive extraction methods, EPEX is fast and reliable. Using atomic force microscopy the size of the particles can be determined from samples extracted from the nanodusty plasma during one growth cycle and can be compared to the results of simultaneously performed in situ Mie polarimetry for the first time. We show that the extraction process can be divided in three distinct phases and that its physics can be understood in the simple framework of the force balance for a single dust particle. Using this single particle model, we present a new method for determining the particle charge of dust particles in dense dusty plasmas. The determined particle charge of (−9.2 ± 2.8) elementary charges reveals a strong Havnes effect. [ABSTRACT FROM AUTHOR]

The path to understanding star formation processes begins with the study of the formation of molecular clouds. The outskirts of these clouds are characterized by low column densities that allow the penetration of ultraviolet radiation, resulting in a nonnegligible ionization fraction and the charging of the small dust grains that are mixed with the gas; this diffuse phase is then coupled to the ambient magnetic field. Despite the general assumption that dust and gas are tightly correlated, several observational and theoretical studies have reported variations in the dust-to-gas ratio toward diffuse and cold clouds. In this work, we present the implementation of a new charged particles module for analyzing the dust dynamics in molecular cloud envelopes. We study the evolution of a single population of small charged grains (0.05 μm) in the turbulent, magnetized molecular cloud envelope using this module. We show that variations in the dust-to-gas ratio arise due to the coupling of the grains with the magnetic field, forming elongated dust structures decoupled from the gas. This emphasizes the importance of considering the dynamics of charged dust when simulating the different phases of the interstellar medium, especially for star formation studies. [ABSTRACT FROM AUTHOR]

The properties (densities of electrons and metastable argon atoms, effective electron temperature and dust charge) of argon/dust and pure argon pulsed plasmas are studied using a spatially-averaged model. The calculated time-dependencies for the densities of electrons and metastable atoms are compared with the experimental measurements and are found to be in a good qualitative agreement. It is analyzed how the plasma properties depend on the shape of the electron energy probability function (EEPF), the pulsing frequency and the duty cycle for both dust-free and dusty plasma. The analysis reveals that the agreement between theory and experiment is better with Druyvesteyn EEPF than the Maxwellian EEPF. Further, the variation in the pulsing frequency νp differently affects the metastable density nm in a dust-free and in a dusty plasma. For large νp, the metastable density in the dust-free pulsed plasma is larger than in the continuous-wave (CW) discharge, while the opposite is obtained in the presence of dust particles. This difference probably arises because of faster variation in the effective electron temperature in the dusty plasma due to collection of electrons by dust particles. Our calculations also show that dust particles may affect the behavior of electron density in the beginning of the on-period due to an enhancement in electron collection by dust particles. [ABSTRACT FROM AUTHOR]

The PK-4 system is a micro-gravity dusty plasma experiment currently in operation on-board the International Space Station. The experiment utilizes a long DC discharge in neon or argon gases. We apply our 2D particle-in-cell with Monte Carlo collisions discharge simulation to compute local plasma parameters that serve as input data for future dust dynamics models. The simulation includes electrons, Ne+ ions, and Nem metastable atoms in neon gas and their collisions at solid surfaces including secondary electron emission and glass wall charging. On the time scale of the on-board optical imaging, the positive column appears stable and homogeneous. On the other hand, our simulations show that on microsecond time scales the positive column is highly inhomogeneous: ionization waves with phase velocities in the range between 500 m s−1 and 1200 m s−1 dominate the structure. In these waves, the electric field and charged particle densities can reach amplitudes up to 10 times of their average value. Our experiments on ground-based PK-4 replica systems fully support the numerical findings. In the experiment, the direction of the DC current can be alternated, which has been found to favor dust particle chain formation. We discuss possible mechanisms for how the highly oscillatory plasma environment contributes to the dust particle chain formation. [ABSTRACT FROM AUTHOR]

The analytical solution of dust-ion-acoustic-solitary waves (DIASWs)with the influence of external periodic force are reported in a dusty plasma model which consists of dust-ion collisions. Using reduction perturbation technique (RPT) damped modified forced Korteweg-de-Vries-Burger (DMFKdVB)equation in some critical composition is obtained. Various physical parameters i.e. dust ion collision frequency (νid0), the entropic index (q), the velocity of travelling wave (M0) ,the ratio of the densities between electrons and ions (μ), viscosity coefficient (η), frequency (w) of the external perturbation and the strength(f0) of the perturbation are observed. This study may be helpful to interpret the characteristics of DIASWs in astrophysical rings, interstellar clouds and comet tails. [ABSTRACT FROM AUTHOR]

A dusty plasma was created in a stratified glow discharge in longitudinal magnetic fields above 1 T. Experimental conditions were selected and dust structures were first created in the neon working gas in the magnetic field range B = 1.1–2.2 T. Under realized conditions, the electron cyclotron radius is close to the dust particle radius, and the ion cyclotron radius is less than the Debye screening length. Images of dust structure cross sections perpendicular to the magnetic field were obtained. They contain about 10 particles. The dependence of the angular velocity of the dust structure rotation for its widest cross section on magnetic field was measured. The direction of the angular velocity vector coincides with the direction of the magnetic induction vector. In contrast to the previously obtained dependence of the rotation velocity on magnetic field in the region B < 1 T, at B > 1 T the rotation angular velocity ceases to grow, reaching a value of about 3 rad s−1. To explain the experimental results on the dust structure rotation velocity, an analytical model of the rotation mechanism is proposed. The model is based on the concept of eddy currents in striations and the influence of the magnetic field on the striation length. The obtained estimates of the rotation velocity are in a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Motivated by the recent experimental realization of ultracold dusty plasma (2019 Sci. Rep. 9 3261), we present the results of particle-in-cell simulation with Monte-Carlo-collisions for wake behind a dust particle due to focusing of ions at superfluid helium temperature (∼2 K). Dynamical screening (wakefield) defines structural and dynamical properties of charged dust particles in plasmas such as phase transition, crystal formation, vibration modes (waves) etc. Here, we delineate in detail the dependence of wake strength on the streaming velocity of ions and on the ion-neutral charge exchange collision frequency (neutrals density) in the ultracold dusty plasma. Lowering the temperature to ultracold level leads to a wake pattern behind a dust particle that completely differs from the wake at normal conditions. For wide range of parameters, most remarkable features of the wakefield are (i) the formation of wake pattern with two maxima split in transverse to ion flow direction in the downstream area, (ii) pronounced inverse V shape of the wakefield closely resembling the wake in quark-gluon plasma and dense quantum plasma (warm dense matter), and (iii) the inter-dust attraction region in transverse direction. The latter shows that molecule-like interaction between dust particles is realized in ultracold dusty plasmas. These observations show a fundamental difference of ultracold dusty plasma physics from well studied complex plasmas at normal conditions. [ABSTRACT FROM AUTHOR]

Sectional models of the dynamics of aerosol populations are well established in the aerosol literature but have received relatively less attention in numerical models of dusty plasmas, where most modeling studies have assumed the existence of monodisperse dust particles. In the case of plasmas in which nanoparticles nucleate and grow, significant polydispersity can exist in particle size distributions, and stochastic charging can cause particles of given size to have a broad distribution of charge states. Sectional models, while computationally expensive, are well suited to treating such distributions. This paper presents an overview of sectional modeling of nanodusty plasmas, and presents examples of simulation results that reveal important qualitative features of the spatiotemporal evolution of such plasmas, many of which could not be revealed by models that consider only monodisperse dust particles and average particle charge. These features include the emergence of bimodal particle populations consisting of very small neutral particles and larger negatively charged particles, the effects of size and charge distributions on coagulation, spreading and structure of the particle cloud, and the dynamics of dusty plasma afterglows. [ABSTRACT FROM AUTHOR]

In the present work, various scenarios of the spatial distributions of argon dusty plasma parameters are considered, focusing on the case of a large density of dust particles. It is shown that in this case a scenario with the inversion of the ambipolar field sign, considered in earlier studies by authors for plasma with heavy negative ions, can be realized. In this case, the ionization inside the dust cloud becomes small in comparison with the volume loss of charges inside the dust cloud, and the lack of charges is compensated by their arrival from the outer peripheral plasma region. This transition is accompanied by the phenomenon of the reversal of the sign of the radial electric field at the boundary of the dust cloud, and the formation of nonmonotonic profiles of the electron density with a shift of the maximum electron density from the center to the periphery. The radial stability of the dust particles cloud is provided by the balance of the increasing dust charge density gradient in the presence of the pushing out ambipolar field. [ABSTRACT FROM AUTHOR]

Incandescent dust particles are observed with the naked eye in plasmas excited at the electron cyclotron resonance produced in pure acetylene. To investigate the heating mechanisms involved and their potential impact on the dust particle charge, as a first approach, a probe is used to measure the floating potential and to estimate the temperature reached by the material. Both highly depend on the position in the magnetic field and on the plasma conditions (pressure and gas, namely argon or helium). Numerical simulations based on the balance of the currents and of the heat fluxes on the probe emphasize a key role of primary electrons: they are responsible for the very negative floating potential as well as for the high probe temperature. Numerical simulations are also adapted to the case of a dust particle in a non-reactive plasma. However, even it can reach temperatures higher than 1600 K, the dust particle remains negatively charged. [ABSTRACT FROM AUTHOR]

The forced vertical oscillations of a single dust particle trapped in a standing striation are investigated. The particle oscillations associated with the displacement of the striation are induced by square wave modulation of the discharge current. Amplitude−frequency characteristics with respect to pressure are measured. The resonance frequency, the logarithmic decrement and the amplitude of resonance peak are determined. In order to obtain the eigenfrequency value, the phase shift of the forced dust particle oscillations is measured and the velocity resonance investigated. The calculation of the dust particle charge is made with the help of the eigenfrequency. A quantitative description of the resonance behaviour of the dust particle based on the theory of the forced harmonic oscillator is made. The Q-factor of a dusty plasma system is measured for the first time, and the obtained value compared with Q-factors of dusty plasma oscillatory systems previously investigated in rf plasma. [ABSTRACT FROM AUTHOR]

Dusty plasma has been studied in dc glow discharge with standing striation formed in neon. The theoretical method of dust particle charge determination is proposed. This method is based on the calculation of the ion and electron fluxes on the dust particle surface in a spatially periodic field of striation. The electron flux is calculated through the use of non-local electron energy distribution function (EEDF), which is formed by inhomogeneous strata potential. The calculation of dust particle charge using proposed theoretical method are compared with those in which the used EEDF was assumed to be Maxwell EEDF. Under the conditions of standing P-striations at low pressures of neon the numerical calculations and the measurements are performed. An experimental method of dust particle charge determination is applied in the dc discharge condition. Discharge current is modulated at low-frequency in order to determine the dust charge through the relaxation oscillation of a single dust particle. The calculation of the dust particle charge with the help of measured frequency and damping coefficient of the oscillations is made. The dust particle charges obtained by using two independent methods are in good agreement. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of the unusual damped Lyα absorption line system (DLA) toward the quasar SDSS J170542.91+354340.2 at a redshift of 2, previously reported by Noterdaeme et al. as one of the very few CO absorbers known to date at high z. This DLA is exceptional in that: (1) its extinction curve is similar to peculiar Milky Way sightlines penetrating star formation regions; (2) its absorption components are redshifted at a speed of several hundred km s−1 compared to broad Balmer emission lines; (3) its gas-phase metallicity is super-solar as evaluated from more than 30 absorption lines; (4) detection of residual flux in the DLA trough and variability of absorption is possible. Based on these facts, we argue that this dusty DLA is a good candidate for an intrinsic quasar 2175 Å absorber, and can originate from star formation regions of the quasar’s host galaxy. We discuss in detail the gas and dust properties, and the dust depletion. Follow-up observations, such as spectropolarimetry and optical/infrared spectroscopy, will help to confirm the system’s intrinsic nature and to explore how dust grains behave in the extreme environments proximate to quasars. [ABSTRACT FROM AUTHOR]

We present the results of a new spectroscopic survey for dusty intervening absorption systems, particularly damped Lyα absorbers (DLAs), toward reddened quasars. The candidate quasars are selected from mid-infrared photometry from the Wide-field Infrared Survey Explorer combined with optical and near-infrared photometry. Out of 1073 candidates, we secure low-resolution spectra for 108 using the Nordic Optical Telescope on La Palma, Spain. Based on the spectra, we are able to classify 100 of the 108 targets as quasars. A large fraction (50%) is observed to have broad absorption lines (BALs). Moreover, we find six quasars with strange breaks in their spectra, which are not consistent with regular dust reddening. Using template fitting, we infer the amount of reddening along each line of sight ranging from A(V) ≈ 0.1 to 1.2 mag (assuming a Small Magellanic Cloud extinction curve). In four cases, the reddening is consistent with dust exhibiting the 2175 Å feature caused by an intervening absorber, and for two of these, an Mg ii absorption system is observed at the best-fit absorption redshift. In the rest of the cases, the reddening is most likely intrinsic to the quasar. We observe no evidence for dusty DLAs in this survey. However, the large fraction of BAL quasars hampers the detection of absorption systems. Out of the 50 non-BAL quasars, only 28 have sufficiently high redshift to detect Lyα in absorption. [ABSTRACT FROM AUTHOR]

A novel mechanism of the formation of compact dusty clouds in astrophysical environments is discussed. It is shown that the balance of collective forces operating in space dusty plasmas can result in the effect of dust self-confinement, generating equilibrium spherical clusters. The distribution of dust and plasma density inside such objects and their stability are investigated. Spherical dusty clouds can be formed in a broad range of plasma parameters, suggesting that this process of dust self-organization might be a generic phenomenon occurring in different astrophysical media. We argue that compact dusty clouds can represent condensation seeds for a population of small-scale, cold, gaseous clumps in the diffuse interstellar medium. They could play an important role in regulating its small-scale structure and its thermodynamical evolution. [ABSTRACT FROM AUTHOR]

Experimental methods are described for determining transport coefficients in a strongly coupled dusty plasma. A dusty plasma is a mixture of electrons, ions and highly charged microspheres. Due to their large charges, the microspheres are a strongly coupled plasma, and they arrange themselves like atoms in a crystal or liquid. Using a video microscopy diagnostic, with laser illumination and a high speed video camera, the microspheres are imaged. Moment-method image analysis then yields the microspheres' positions and velocities. In one approach, these data in the particle paradigm are converted into the continuum paradigm by binning, yielding hydrodynamic quantities like number density, flow velocity and temperature that are recorded on a grid. To analyze continuum data for two-dimensional laboratory experiments, they are fit to the hydrodynamic equations, yielding the transport coefficients for shear viscosity and thermal conductivity. In another approach, the original particle data can be used to obtain the diffusion and viscosity coefficients, as is discussed in the context of future three-dimensional microgravity experiments. [ABSTRACT FROM AUTHOR]

An experimental study of dust grain dynamics in plasma was carried out for cluster systems relaxing to their equilibrium state after the action of a laser beam. The influence of this external perturbation on the potential between interacting dust grains was analyzed. We found that the spatial asymptotes of the pair potential for perturbed and equilibrium dust systems differ. The possible reasons for this phenomenon are discussed. [ABSTRACT FROM AUTHOR]

Strongly coupled plasmas in which the interaction energy exceeds the kinetic energy play an important role in many astrophysical and laboratory systems including compact stars, laser plasmas and dusty plasmas. They exhibit many unusual collective properties, such as liquid or crystalline behaviour, peculiar oscillation spectra and transport properties. Recently, strongly coupled plasmas were studied in the presence of a strong magnetic field by computer simulations, and strong modifications of their transport properties and oscillation spectra were observed. While strong magnetization is common in stellar systems it is practically impossible to achieve in complex plasmas due to the large mass of the dust particles. Here we discuss a recently demonstrated approach to achieve very strong 'magnetization' by a rotation of the neutral gas, and we present new results for macroscopic two-dimensional systems. [ABSTRACT FROM AUTHOR]

The electric charge on silica microparticles (5µm in diameter) levitating in the sheath of an rf discharge plasma is determined in a newly installed device for dusty plasma experiments at the IASST. The sheath potential profile is measured using an emissive probe and the electric field is obtained in order to determine the dust charge. The measured dust charge in the pressure range 0.50-5.0 Pa using the electric field value at the levitation height is found to be of the order of 104 elementary charges. Dust charge is also examined using the vertical resonance method which gives a similar order of charges. The experimentally measured charge is compared with the estimated values based on the orbital motion limited charging model. The coupling strength between the particles forming a 2D plasma crystal lattice is estimated using the measured dust charge. [ABSTRACT FROM AUTHOR]

The effects of impurity on eigenmodes in one-dimensional dusty plasma lattices are studied. It is found that local modes can be excited besides lattice waves, due to the existence of an impurity particle. The dispersion relations of the modes are derived accordingly. Properties of the lattice and local modes are also analyzed and discussed, particularly for their symmetric features and conditions of the mode excitation. [ABSTRACT FROM AUTHOR]

In this paper, a damped nonlinear Schrodinger equation governing dust acoustic solitary waves is obtained in collisional dusty plasmas being comprised of dust grains with dust charge variation, Boltzmann distributed electrons and nonthermally distributed ions. The modulation instability (MI) of dust-acoustic waves is studied and the expression of the MI growth rate is given. The numerical results show that the nonthermal ions, collision effect and ion-to-electron temperature ratio have a strong influence on the existential region of different types of similaritons and the amplitude of similaritons. Furthermore, the different interactions of two similaritons are investigated. [ABSTRACT FROM AUTHOR]

The effect of dust size distribution in ultracold quantum dusty plasmas are investigated in this paper. How the dispersion relation and the propagation velocity for the quantum dusty plasma vary with the system parameters and the different dust distribution are studied. It is found that as the Fermi temperature of the dust grains increases the frequency of the wave increases for large wave number dust acoustic wave. The quantum parameter of Hd also increases the frequency of the large wave number dust acoustic wave. It is also found that the frequency o0 and the propagation velocity n0 of quantum dust acoustic waves all increase as the total number density increases. They are greater for unusual dusty plasmas than those of the usual dusty plasma. [ABSTRACT FROM AUTHOR]

The charged dust effect on stability of a magnetized rotating plasma is analysed using approximation of immobile dust. In the presence of the dust, a term with the electric field appears in the one-fluid equation of plasma motion. This electric field affects the equilibrium plasma rotation and also gives rise to a family of instabilities of the rotating plasma called dust-induced rotational instabilities (DRIs). The DRIs are related to the charge imbalance between the plasma ions and electrons because of the charged dust. In contrast to the well-known magnetorotational instability driven by the radially decreasing plasma rotation frequency, the DRI can appear for an arbitrary rotation frequency profile. A mathematical technique for the analysis of the magnetorotational phenomena is presented. It is based on the one-fluid magnetohydrodynamic approach developed for a pure plasma and generalized to include the immobile dust effects. The mode equation and local dispersion relation are derived in terms of the canonical parameters. [ABSTRACT FROM AUTHOR]

We report on observations of cusp-like sharply peaked dust acoustic solitons in a one-dimensional fluid simulation of a dusty plasma system. These nonlinear singular structures, dithering at the wave breaking point, are found to be long-lived entities that emerge spontaneously from a variety of largeamplitude initial perturbations. Such excitations can play a significant role in wave breaking and wave-particle dynamics in dusty plasmas and may explain some recent experimental observations. [ABSTRACT FROM AUTHOR]

Nonplanar (cylindrical and spherical) double layers (DLs) in a quantum dusty plasma (composed of inertial ions, Fermi electrons and negatively charged immobile dust particles) are studied by employing the reductive perturbation method. The modified Gardner equation describing the nonlinear propagation of the quantum dust ion-acoustic (QDIA)waves is derived, and its nonplanarDL solutions are numerically analyzed. The parametric regimes for the existence of the DLs, which are found to be associated with both positive and negative potentials, are obtained. It has been found that the existence of small but finite-amplitude electrostatic DLs depends on µ = Zdnd0/ni0 (where Zd is the number of electrons residing onto the dust grain surface, and nd0 and ni0 are, respectively, the dust and ion number density at equilibrium) as well as the quantum diffraction parameter H. It has also been found that the propagation characteristics of nonplanar QDIA DLs are significantly different from those of the planar ones. [ABSTRACT FROM AUTHOR]

For two-dimensional unmagnetized dusty plasmas with many different dust grain species, a Kadomtsev-Petviashvili (KP) equation, a modified KP (mKP) equation and a coupled KP(cKP) equation for small, but finite amplitude dust-acoustic solitary waves are obtained for different physical conditions respectively. The influence of an arbitrary dust size distribution described by a polynomial expressed function on the properties of dust-acoustic solitary waves is investigated numerically. How dust size distribution affects the sign and the magnitude of nonlinear coefficient A (D) of KP (mKP) equation is also discussed in detail. It is noted that whether a compressive or a rarefactive solitary wave exists depends on the dust size distribution in some dusty plasmas. [ABSTRACT FROM AUTHOR]

Based on the hydrodynamic equations, the characteristics of nonlinear dust-ion-acoustic shock propagation in an inhomogeneous dusty plasma are numerically studied, by means of the fifth-order weighted essentially non-oscillatory (WENO) finite difference scheme. The inhomogeneous dust charging process for different plasma parameters has been incorporated and its effect on the shock propagation has been investigated. Comparisons of the shocks in the cases of different ion density distributions and different electron-to-ion density ratios are presented. The results show that the dust charging process results in wave damping and dissipation, and the decrease of the electron-to-ion density ratio leads to the increase of the speed, amplitude and width of the shock front. Moreover, the dispersion effect is dominant in the case of sharp shocks whereas the smooth shocks are easily dissipated. [ABSTRACT FROM AUTHOR]