Micron-sized Dust Particles Research Articles

Height-modulating horizontal transport of dust particles in a dusty plasma ratchet

Dust particles are often electrostatically trapped and levitated within the non-electroneutral region of a sheath. The fascinating transport phenomena of dust particles strongly depend on the plasma parameters surrounding them within the sheath, whereas, that are quite difficult to obtain, leading to an unclear understanding of particle transport mechanisms. Here, we demonstrate a tunable horizontal transport of micron-sized dust particles by precisely manipulating their vertically suspended heights in an asymmetric ratchet sheath by designing dusty plasma ratchet. A collection of dust particles serves as micro-probes to detect the height-dependent transport properties and the feature of the sheath. Two methods are employed to lift or reduce the suspended heights of dust particles while maintaining the sheath unchanged. As the suspended heights of dust particles vary, their directional transport changes accordingly, including a flow reversal. A two-dimensional model of the ratchet sheath depicts the nonlinear distributions of plasma parameters and reveals that these unexpected transport phenomena can be attributed to the dependence of the electric ratchet potential and the resulting non-equilibrium net ion drag force on the suspended heights of dust particles. Our combined experimental and theoretical study provides insights into the fundamental transport properties of dust particles in an asymmetrical sheath.

Study on the characteristics of compound dust source pollution and foam dust suppression technology in coal mine anchor excavation production

To guard against the damage caused by the dust pollution of the shuttle driver in the anchor excavation production, the Discrete Phase Model(DPM)-Discrete Element Model(DEM) was constructed based on the gas-solid two-phase flow theory, the dust pollution characteristics of the shuttle transfer stage were numerically simulated, and a dual carborne combined foam dust suppression system was developed. The results showed that at the rear of the transfer machine, due to the reduction of the roadway section space during transferring made the wind velocity relatively maximum, and the space after transferring dispersed many cutting dust and transferring dust, resulting in the wind velocity after transferring was slightly smaller than before transferring, and the wind velocity difference was 0.18 m/s on average. The dust pollution in the operating environment of the shuttle driver before, during and after transferring was more serious, with 162.1 mg/m³, 340.7 mg/m³ and 540.8 mg/m³. There was variability in the particle diameter of dust generated by different processes, and smaller micron-sized dust particles were generated during transferring, of which respiratory dust below 7.07 μm accounted for up to 21% of the total. To reduce the high concentration of respiratory dust clusters, a strong wettability high-fold foam dust suppressant was prepared and applied to a dual carborne combined foam dust suppression system, and the average dust reduction rates of total dust and respiratory dust reached 91.9% and 93.6%, respectively.

Characterization of 10 nm – 10 μm coal dust particles generated by simulated different cutting and drilling parameters: mass concentration distribution, number concentration distribution, and fractal dimension

Nano-to-micron-sized coal dust can cause coal workers’ pneumoconiosis (CWP), and cutting and drilling are the main coal dust-generating processes. Based on a self-developed simulated coal cutting and drilling dust generation system, the effects of cutting parameters (tooth tip cone angle, impact angle, roller rotary speed, cutting speed) and drilling parameters (drill bit diameter, drilling speed) on the mass concentration distribution, number concentration distribution and fractal dimension of 10 nm – 10 μm coal dust were investigated. Results show that the mass concentration of 10 nm – 10 μm coal dust generated by cutting/drilling peak at 5.7 – 7.2 μm, while the number concentrations during cutting and drilling respectively peak at 60 – 90 nm and 20 – 30 nm. During both cutting and drilling processes, the generated coal dust particles in 10 – 300 nm account for > 90% of the total 10 nm – 10 μm coal particles, while PM2.5 in PM10 is generally below 18%. It is also found that smaller tooth tip cone angle, larger impact angle, lower roller rotary speed, smaller drill bit diameter, or lower drilling speed can reduce the generation of 10 nm – 10 μm coal dust with a fractal dimension of 0.94 – 1.92. This study reveals the distribution characteristics of nano- to micron-sized coal dust particles under different cutting and drilling parameters, and the research results can serve as reference for adjusting cutting and drilling parameters to lower down the 10 nm – 10 μm coal dust generation and thus prevent the CWP.

INVESTIGATION OF THE PROPERTIES OF MICROPARTICLES IN THE GLOW DISCHARGE STRATUM IN A CROSSED ELECTRIC AND MAGNETIC FIELD

In this work, the behavior of charged micron-sized particles in the DC glow discharge stratum at low pressure in a crossed magnetic and electric field was experimentally studied. The experiment was conducted in a vertically oriented gas-discharge glass tube. A homogeneous magnetic field was created using a two-section Helmholtz coil. The results showed that the micron-sized dust particles move in the opposite direction to the ExB drift as the magnetic field induction increases. Once the induction reaches a specific threshold (B>10 mT), the dust particles start rotating and forming counter-rotating vortex pairs on the horizontal plane. Moreover, it was observed that the shape of the dust structures changes from a disk to an ellipsoid. The PIV (particle image velocimetry) method was employed to analyze the dust vortices' dynamic behavior, and the generation of the co-vortex rotation was explained through the dust particles' charge gradient, which was orthogonal to the ion drag force.

Interpebble contact radius in a comet nucleus

ABSTRACTIn recent years, the gravitational collapse of pebble clumps in the early Solar system has been regarded as a plausible scenario for the origin of comets. In this context, ‘pebbles’ represent mm- to cm-sized dust aggregates composed of (sub)micron-sized dust particles, and the structure of km-sized comets is thought to be an agglomerate of pebbles. The contact radius for pebble–pebble contacts was modelled in an earlier study; however, the pressure dependence of the interpebble contact radius was not considered. Here, we revisit the interpebble contact radius in a comet nucleus. We calculated the interpebble contact radius based on JKR contact theory, and we took into consideration the effect of lithostatic pressure. We found that the interpebble contact radius varies with depth from the surface, and the earlier model underestimated it by one order of magnitude at the centre of the comet nucleus.

Microphysics of dust in a distant comet C/2017 K2 (PanSTARRS) retrieved by means of polarimetry

We conducted the earliest polarimetric survey of Comet C/2017 K2 (PanSTARRS) over 10 epochs during February–March 2021, while the comet's heliocentric distance was decreasing from 7.135 au to 6.801 au. Within an aperture radius ρ = 10,000 km, we found slightly varying negative polarization with median value PQ ≈ –2.1% at phase angle α ≈ 8° This appears in quantitative agreement with measurements of other distant comets. The negative polarization reveals submicron and micron-sized dust particles within the coma constrain the imaginary part of the refractive index in at least one type of particles to Im(m) ≤ 0.04. Models earlier developed in Kochergin et al. [1] for the negative polarization in distant Comet 29P/Schwassmann–Wachmann are similar to the negative polarization of Comet C/2017 K2 (PanSTARRS), suggesting its coma could be populated by Mg-rich silicate particles and/or water-ice particles, which are mixed with organic particles and/or amorphous-carbon particles. Modeling dust motion suggests that the inner coma is populated by particles whose age is up to 15 days since their emanation from the nucleus.

Test charge driven response of a dusty plasma with polarization force

By using the framework of kinetic model, the test charge driven response of a dusty plasma is evaluated in the presence of polarization force. The plasma containing electrons, singly ionized positive ions, and highly charged negative dust particulates is known as a dusty plasma, which can be perturbed by a test particle of charge qT moving with velocity vT along the z-axis. The polarization force purely comes from the high charging state of micron-sized dust particles, causing a deformation of shielding length due to density gradient and modifying the collective motion and particulates’ acceleration. The application of Fourier transformation technique to the set of dynamical equations may result in the shielded potential for a test charge with a modified dielectric constant. Several possibilities have been explored to evaluate the shielded potentials by imposing different conditions on the test charge speed in comparison with the thermal speeds of plasma species. It is found that the profiles of wakefield, Debye-Hückel and farfield (FF) potentials are strongly modified by the polarization force coefficient via the dust charging state and dust concentration. The present findings are useful in the study of strongly coupled dusty plasma, where micron-sized negatively charged dust grains are characterized by a high charging state.

Dust adhesion and deposition behavior in internal cooling duct with pin fins

The collision-adhesion and deposition of micron-sized dust particles in the internal cooling duct with pin fin arrays are investigated, integrating the energy dissipation collision model of spherical particles and gas-solid two-phase theory. The effects of particle Stokes number (Stk = 0.12, 0.48, and 3), particle temperature (Tp = 1173, 1223, 1273, and 1343 K), and streamwise pin spacing (S = 2.5, 3, and 3.75D) on the collision ratio, sticking ratio and deposition ratio of particles on pin fins and endwalls are investigated when the inlet Reynold number is 36,575. The results show that the pin collision ratio rises drastically with the increase of particle size, while the sticking ratio decreases. The particle temperature has a minimal impact on the collision ratio, sticking ratio, and deposition ratio when particle temperature is below 1273 K. However, the collision ratio of particles on the pins decreases appreciably when the particle temperature increases further up to 1343 K, while the sticking ratio increases significantly. The pin fin arrays with the streamwise spacing of 3D and 3.75D reduce the number of endwall deposition of particles with Stokes number of 0.12, compared to the pin fin array with a streamwise spacing of 2.5D. The windward region of the pin shows the largest potential for dust deposition and the maximum deposition height occurs at the junction of the pin-endwall. Moreover, the deposits on the pin fin grows and tends to be more uniform with the increase of particle temperature, according to the deposition profile on the pin.

Electrostatic dust ejection from asteroid (3200) Phaethon with the aid of mobile alkali ions at perihelion

The asteroid (3200) Phaethon is known to be the parent body of the Geminids, although meteor showers are commonly associated with the activity of periodic comets. What is most peculiar to the asteroid is its comet-like activity in the ejection of micrometer-sized dust particles at every perihelion passage, while the activity of the asteroid has never been identified outside the near-perihelion zone at 0.14au from the Sun. From the theoretical point of view, we argue that the activity of the asteroid is well explained by the electrostatic lofting of micrometer-sized dust particles with the aid of mobile alkali ions at high temperatures. The mass-loss rates of micrometer-sized particles from the asteroid in our model is entirely consistent with the values inferred from visible observations of Phaethon’s dust tail. For millimeter-sized particles, we predict three orders of magnitudes higher mass-loss rates, which could also account for the total mass of the Geminid meteoroid stream by the electrostatic lofting mechanism.

Dynamics of the interaction of dust particles with the LHC beam

Micrometer-sized dust particles present in the Large Hadron Collider (LHC) beam pipe are believed to have caused many thousands of sporadic beam loss events around the LHC. These so-called unidentified falling objects (UFOs) have been under continuous study since the start of high intensity beam operation in the LHC due to their impact on the LHC availability: 139 beam dumps and 12 magnet quenches during Run II (2015--2018) alone. To mitigate the impact of UFOs on future accelerators such as the High Luminosity LHC and the Future Circular Collider, it is fundamental to foster a better understanding of these beam loss events. In this paper, key observations made since the start of LHC operation are summarized and the prevailing UFO hypothesis is confronted by a compilation of observations acquired during Run II. In particular, it is shown that UFOs must carry an initial negative charge before entering the proton beam, or that they are by some other means accelerated toward the beam not only by gravity. A simulation model for the dynamics of the dust particles and their interaction with the beam was developed over the years. This model is improved and validated by measurements. It is however also shown that a subset of observed beam losses, which contain a positive time profile skewness, cannot be explained by it.

Dynamic charging effect on electromagnetic wave in low $\beta $ plasmas

Low beta plasma system is chosen for the study of low frequency electromagnetic Shear Alfven waves exhibiting dynamical charging of micron/sub micron size dust particles. A semi classical Quantum Hydrodynamic Model (QHD) is employed which includes the quantum effects for plasma electrons in the terms of statistical degenerate pressure, Landau quantization, exchange-correlation potential, and tunneling potential. The low beta plasma characteristics provides the opportunity for the usage of two potential theory in order to derive a complex equation of dispersion of the shear Alfven wave in quantum dusty magneto plasmas. Analytical simplification of dispersion equation provides the damping rate of the Shear Alfven wave which is verified graphically for a typical set of parameters. It is noticed that the damping rate depends upon the quantum properties of Landau quantization, exchange-correlation, and tunneling potential in addition to the dust radius which modifies the floating potential of the dust particles. This work may seek its applications in the astrophysical objects in general, and in the semiconductor laboratory plasmas for particular dust size and magnetic field.

Gravitoviscous protoplanetary disks with a dust component

Aims. We study the dynamics and growth of dust particles in circumstellar disks of different masses that are prone to gravitational instability during the critical first Myr of their evolution. Methods. We solved the hydrodynamics equations for a self-gravitating and viscous circumstellar disk in a thin-disk limit using the FEOSAD numerical hydrodynamics code. The dust component is made up of two different components: micron-sized dust and grown dust of evolving size. For the dust component, we considered the dust coagulation, fragmentation, momentum exchange with the gas, and dust self-gravity. Results. We found that the micron-sized dust particles grow rapidly in the circumstellar disk, reaching a few cm in size in the inner 100 au of the disk during less than 100 kyr after the disk formation, provided that fragmentation velocity is 30 ms−1. Due to the accretion of micron dust particles from the surrounding envelope, which serves as a micron dust reservoir, the approximately cm-sized dust particles continue to be present in the disk for more than 900 kyr after the disk formation and maintain a dust-to-gas ratio close to 0.01. We show that a strong correlation exists between the gas and pebble fluxes in the disk. We find that radial surface density distribution of pebbles in the disk shows power-law distribution with an index similar to that of the Minimum-mass solar nebula regardless the disk mass. We also show that the gas surface density in our models agrees well with measurements of dust in protoplanetary disks of AS 209, HD 163296, and DoAr 25 systems. Conclusions. Pebbles are formed during the very early stages of protoplanetary disk evolution. They play a crucial role in the planet formation process. Our disc simulations reveal the early onset (<105 yr) of an inwards-drifting flux of pebble-sized particles that makes up approximately between one hundredth and one tenth of the gas mass flux, which appears consistent with mm-observations of discs. Such a pebble flux would allow for the formation of planetesimals by streaming instability and the early growth of embryos by pebble accretion. We conclude that unlike the more common studies of isolated steady-state protoplanetary disks, more sophisticated global numerical simulations of circumstellar disk formation and evolution, including the pebble formation from the micron dust particles, are needed for performing realistic planet formation studies.

A study of SCL sheath in presence of two dust species in a photoemissive environment

We have presented a basic model for a one dimensional collisionless space charge limited (SCL) plasma sheath consisting of electrons, ions, and two kinds of dust populations—a nano-dust population and a micrometer sized dust population. We have assumed that the nano-dust particles, plasma electrons, photoelectrons, and ions are the constituents of the plasma fluid and the micrometer sized dust particles behave as suspended impurities in the plasma without affecting the plasma dynamics. We have assumed that the charges of the micrometer-dusts are determined from the current balance on them and the charges on the nano-dusts are fixed. Due to photoemission, like the lunar surface charges to a positive potential, so the nano-dust and micrometer-dust particles charge to a positive potential. The electron densities have been derived by assuming both the electrons and photoelectrons to be Maxwellian, whereas the ion and nano-dust densities are derived from energy conservation of the ions and nano-dust particles and the continuity equations. Being a constituent of plasma, the nano-dusts do affect the sheath dynamics through the Poisson equation, which determines the plasma potential in the sheath region. The typical conditions for the levitation of dust particles in an SCL sheath including the maximum height and maximum size of the particles are calculated.

Dust-density waves in radio-frequency discharges under magnetic fields

Experiments on self-excited dust-density waves under various magnetic fields have been performed. For that purpose, different dust clouds of micrometer-sized dust particles were trapped in the sheath of a radio frequency discharge. The self-excited dust-density waves were studied for magnetic field strengths ranging from 0 mT to about 2 T. It was observed that the waves are very coherent at the lowest fields (B < 20 mT). At medium fields (20 mT < B<300 mT), the waves seem to feature a complex competition between different wave modes before, at even higher fields, the waves become more coherent again. At the highest fields (above 1 T), the wave activity is diminished. The corresponding wave frequencies and wavenumbers have been derived. From the comparison of the measured wave properties and a model dispersion relation, the ion density and the dust charge are extracted. Both quantities show only little variation with magnetic field strength.

Investigation of optical glass characteristics under the influence of space factors

The paper describes a DF-OPTICS device that the present authors designed for the experimental study of changes in the optical properties of a glass whose surface is exposed to high-speed flows of micron-sized dust particles. The device allows the scattering indicatrix and the spectral transmittance to be automatically measured at each point of the sample with a 0.5-mm increment. Advantages of the developed device include small dimensions and the ability to work in vacuum, allowing it to be used in an accelerator chamber to simulate outer space factors. Experimental results for the K-8 glass put in a microparticle accelerator and bombarded by an aluminum powder PAP-1 with a characteristic size of 1-3 µm and speeds of 2-8 km / s are presented. The device makes it possible to measure the change of the spectral transmittance of transparent materials in the UV and RGB regions with an accuracy of 0.005%, which exceeds the sensitivity of some known spectrophotometers.

Dynamics and transport of magnetized two-dimensional Yukawa liquids

Laboratory dusty plasma typically refers to a collection of micron-sized solid dust particles immersed in the plasma environment, as a result, these dust particles are negatively charged to thousands of elementary charges. Due to the electrical shielding provided by free electrons and ions, the interaction between these dust particles can be modeled as the Yukawa potential. These dust particles are strongly coupled due to their high charges, so that they exhibit collective behaviors of solids and liquids. Magnetic fields are often experimentally introduced in the modulation of dusty plasmas, and later the equivalent “magnetized” dusty plasma experiment is performed, so that magnetized Yukawa systems can be experimentally achieved now. Here, we review a series of results of collective behaviors and different transport processes of magnetized two-dimensional (2D) Yukawa liquids from Langevin dynamical simulations. From the obtained spectra of the simulation results, the vibrational density of states has only one dominant peak frequency, which can be analytically expressed as a function of the cyclotron and plasma frequencies, suggesting that the cyclotron motion of dust particles has been coupled with their thermal motion. It is also found that the statistics of particle motion with a strong magnetic field tend to deviate from the classical Maxwellian distribution. When the ratio of the cyclotron and plasma frequencies for dust particles is around the order of unity, the motion of dust particles tends to be superdiffusive. As the magnetic field increases, the shear viscosity increases with the magnetic field when the Yukawa liquid is cold; however, when the Yukawa liquid is hot, the variation trend of shear viscosity is reversed. It is also found that the structural relaxation time and the diffusion coefficient can be described as a power law relationship with two distinct values of the exponent at low and high temperatures, respectively.

Natural nonlinear convection of dusty fluid in a suspension of multi-wall carbon nanotubes nanoparticles with different temperature of water and suction

This study addresses the nonlinear free convective flow of a conducting dusty nanofluid (multi wall carbon nanotubes + water + micrometer sized dust particles) over a stretched cylinder at different temperatures (10 °C and 50 °C) in the presence of Cattaneo–Christov heat flux, heat source. The mainly arising equations of motion such as continuity, momentum and energy are simplified with the suitable dimensionless variables and solved numerically using the Runge–Kutta method. A numerical simulation is executed with inclusion of multi-wall carbon nanoparticles and dust particles into different temperatures (10 °C and 50 °C) of base fluid water. Calculations for the wall friction coefficient and Nusselt number are carried out and demonstrated in tables. To authenticate the attained results we have offered the comparison with the already published results. A few graphical pictures are plotted to scrutinize the physical insight of the numerically modeled problem for the several flow parameters and found that the multi-walled carbon nanotubes + water at 10 °C dusty nanofluid shows better heat and mass transfer rate compared to temperature at 50 °C. Due to nonlinear convection the friction factor is reduced in the presence of the magnetic field. The Biot number encourages the wall friction, heat and mass transfer rates of both cases.

Micro-dynamics of neutral flow induced dusty plasma flow

We present a detailed experimental study of gas flow induced motion of dust particles in a DC glow discharge plasma. The characteristics of the dust dynamics are investigated as a function of the differential gas flow rate, the background neutral pressure, the dust particle size, and the neutral species of the gas. The experiments have been carried out in the table top Dusty Plasma Experimental (DPEx) device in which a plasma is created between a disk shaped anode and a grounded cathode in a Π-shaped Pyrex glass tube. The asymptotic steady state flow velocity of the injected micron sized dust particles is found to increase with an increase in neutral flow velocity and decrease with an increase in the background pressure. Furthermore, this velocity is seen to be independent of the size of the dust particles, but decreases with an increase in the mass of the background gas. A simple theoretical model, based on estimates of the various forces acting on the dust particles, is used to elucidate the role of neutrals in the flow dynamics of the dust particles. Our experiments thus provide a detailed microscopic understanding of some of the past phenomenological observations of dust flows in the DPEx device and can prove useful in future experimental implementations of dust flow experiments.

Interpolating light-scattering properties of irregularly shaped, absorbing particles.

Success in developing remote-sensing methods is largely based on adequate modeling of target-particle shapes. In various terrestrial and cosmic applications, submicrometer- and micrometer-sized dust particles appear to have a highly irregular morphology. Light scattering by such irregularly shaped particles can be computed only with a numerical technique that, in practice, is a time-consuming approach, demanding significant computational resources. In this Letter, we discuss an efficient way to accelerate light-scattering computations through interpolation of the numerical results obtained at different levels of material absorption. We find a nonlinear dependence of reflectance, degree of linear polarization, and linear and circular polarization ratios on the imaginary part of refractive index Im(m). Over the range of ΔIm(m)=0.05, the dependence can be satisfactorily described with a cubic polynomial function, whose determination requires exact computations at four different values of Im(m). The light-scattering characteristics at other intermediate values of Im(m) can be inferred with great accuracy via interpolation.

Trajectory measurements for individual dust particles on the Colorado dust accelerator

The Dust Coordinate Sensor (DCS) is a dual detector instrument located on the beamline of the 3 MV hypervelocity dust accelerator at the University of Colorado Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT). This instrument non-destructively measures the three-dimensional trajectories of charged, hypervelocity (3–8 km/s), micron-sized dust particles in flight by utilizing the image charge induced on grids of wire electrodes. Where previous peak detection was typically limited to dust particles carrying charges >∼100 fC, new signal processing techniques developed for DCS allow for effective trajectory measurements on particles carrying charges as small as 6 fC. The new signal processing also effectively eliminates false signal detections completely. The position measurements are matched by timestamp to the charge and velocity for each launched dust particle. Verification of the system was performed with independent impact location measurements on a target placed in the beamline. These measurements agree to within 1 mm2 of the predicted locations using DCS trajectories. This study demonstrates the capability of the instrument including new processing methods. Precise trajectory measurement along the beamline enables new options for instrument calibration, scientific experiments, and improvement of the accelerator performance.