Electric Charge Of Dust Particles Research Articles

Influence of dust particles on ionization equilibrium in partially ionized plasmas.

A chemical model is proposed for a dusty plasma consisting of electrons, ions, neutrals, and positively charged dust particles all being at thermodynamic equilibrium. An expression is derived for the Helmholtz free energy, which comprises the ideal part, taking into account the charge of dust particles, and the excess part, evaluated in the framework of the self-consistent chemical model [Phys. Rev. E 83, 016405 (2011)PLEEE81539-375510.1103/PhysRevE.83.016405]. The ionization potential depression for a dust-free partially ionized hydrogen is analytically evaluated for weakly and strongly ionized states to consistently account for the presence of charged and neutral components. An ad hoc interpolation of the ionization potential depression, valid across the whole ionization region, is put forward and subsequent solution of the generalized Saha equation is found to be in a perfect agreement with exact calculations. Minimization of the Helmholtz free energy of dusty plasmas provides the number densities of free electrons, free ions, neutrals, and the dust electric charge as well. Based on consideration of weakly and strongly ionized states, a straightforward comparison is made of the ionization equilibrium in a partially ionized plasma with and without dust particles to demonstrate that at thermal equilibrium positively charged dusts are responsible for an increase in the number density of free electrons and a decrease in the number density of free ions. It is analytically proved that nonideality effects result in a growth of the number densities of free electrons and ions by obtaining the so-called electron and proton ionization potential depressions. Electric charge of dust particles is systematically studied as a full plasma component rather than considering a detailed balance of the electron and ion fluxes on the surface of a solitary dust grain.

Charged Particles of Dust, Electrical Discharges, and the Generation of Vortices in Atmospheres of Planets and the Moon

We consider the features of the mechanisms of the electric charging of dust particles, emergence of electric fields, and discharges in the atmospheres of planets and near the surface of the Moon. We find a significant difference in the nature of the influence of electric fields (discharges) on the vortex motions of two-phase (gas and dust) in the atmospheres of the planets and single-phase (dust) near the surface of the Moon.

A simple method of dust charge estimation using an externally applied oscillating electric field

A new estimation method on the electric charge quantity of dust particles in a complex plasma is developed. This method estimates the mean electric charge of dust particles in a measurement domain. The measurement system is simple and there is not much influence on experimental conditions of a dust phenomenon in which we are interested. The experimental result obtained with this method is compared with theoretical estimations. It is confirmed that the new method provides a quantitatively correct electric charge of dust particles.

On the photoelectric quantum yield of small dust particles

Photoelectron emission is crucial to electric charging of dust particles around main-sequence stars and gas heating in various dusty environments. An estimate of the photoelectric processes contains an ill-defined parameter called the photoelectric quantum yield, which is the total number of electrons ejected from a dust particle per absorbed photon. Here we revisit the so-called small particle effect of photoelectron emission and provide an analytical model to estimate photoelectric quantum yields of small dust particles in sizes down to nanometers. We show that the small particle effect elevates the photoelectric quantum yields of nanoparticles up to by a factor of $10^3$ for carbon, water ice, and organics, and a factor of $10^2$ for silicate, silicon carbide, and iron. We conclude the surface curvature of the particles is a quantity of great importance to the small particle effect, unless the particles are submicrometers in radius or larger.

Electric Charge of Dust Particles in a Plasma

AbstractThe problem of calculation of the electric charge of dust particles in a plasma is considered from different points of view. At first the charging of polarizable dust particles is studied within the orbital motion limited approach. Secondly, the plasma electrodynamics is applied to show that the electric charge of a dust particle is determined by the normal component of the dielectric displacement vector near the grain surface rather than the normal component of the electric field strength. And, finally, the chemical model, initially proposed for determination of partially ionized plasma composition, is demonstrated to be very productive in evaluating the electric charge of the dust component. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

ELECTRIC CHARGING OF DUST AGGREGATES AND ITS EFFECT ON DUST COAGULATION IN PROTOPLANETARY DISKS

ABSTRACT Mutual sticking of dust aggregates is the first step toward planetesimal formation in protoplanetary disks. In spite that the electric charging of dust particles is well recognized in some contexts, it has been largely ignored in the current modeling of dust coagulation. In this study, we present a general analysis of the dust charge state in protoplanetary disks, and then demonstrate how the electric charging could dramatically change the currently accepted scenario of dust coagulation. First, we describe a new semianalytical method to calculate the dust charge state and gas ionization state self-consistently. This method is far more efficient than previous numerical methods, and provides a general and clear description of the charge state of a gas–dust mixture. Second, we apply this analysis to compute the collisional cross section of growing aggregates taking their charging into account. As an illustrative example, we focus on early evolutionary stages where the dust has been thought to grow into fractal (D ∼ 2) aggregates with a quasi-monodisperse (i.e., narrow) size distribution. We find that, for a wide range of model parameters, the fractal growth is strongly inhibited by the electric repulsion between colliding aggregates and eventually “freezes out” on its way to the subsequent growth stage involving collisional compression. Strong disk turbulence would help the aggregates to overcome this growth barrier, but then it would cause catastrophic collisional fragmentation in later growth stages. These facts suggest that the combination of electric repulsion and collisional fragmentation would impose a serious limitation on dust growth in protoplanetary disks. We propose a possible scenario of dust evolution after the freezeout. Finally, we point out that the fractal growth of dust aggregates tends to maintain a low ionization degree and, as a result, a large magnetorotationally stable region in the disk.

Relaxation of dusty plasmas in plasma crystals

Relaxation phenomena in two-dimensional (2D) plasma crystals have been investigated, including both the self-consistent electric charge of dust particles and the electron and ion velocity distribution functions, by means of a modified 2D particle-in-cell (PIC) method. The results obtained show that the mutual interaction of dust particles in such crystals leads to special properties of the background electrons and ions due to their selective collection by dust particles during the relaxation. These electrons and ions can behave as non-ideal components of dusty plasmas in plasma crystals even in cases where their numbers in the Debye cube are large. This effect is caused by their intensive charge exchange with dust particles, which provides dusty plasmas with the status of open statistical systems. The selective collection of electrons and ions by dust particles also causes their deviation from the initial equilibrium as well as the non-equilibrium evolution of the self-consistent electric charge of the dust particles. Relaxation phenomena in plasma crystals have to be taken into account in all cases of strong changes of plasma parameters, for example due to strong oscillations and waves in these crystals.

Relaxation of Background Electrons and Ions in Plasma Crystals

AbstractThe Liouville equation is considered for the statistical system consisting of identical constructureless free particles and grains initially. It relaxes then due to a collection of the particles by the grains. Dusty plasmas are particular cases of this system. The free and collected particles are considered as a common sub‐system which is described by the common whole distribution function. It is shown that this sub‐system is described by the complex integral‐differential equation which can be expected to lead to Non‐Markovian kinetics.Computer modeling shows that background electrons and ions can be non‐ideal components of relaxing dusty plasmas in plasma crystals due to the intensive charge exchange of electrons and ions with dust particles even in the cases where their numbers in the Debye cube are large. The selective collection of electrons and ions by dust particles causes their deviation from the initial equilibrium as well as the non‐equilibrium evolution of the self‐consistent electric potential and electric charge of dust particles.

New results in studies of electric charging of dust particles

An electrodynamic quadrupole inside an ultra-high-vacuum chamber was used to trap particles of micron and submicron sizes, which were charged by electron and ion beams of energies up to 5keV. The Q m - ratios of the particles were derived from measurements of particle oscillation frequencies in the quadrupole. The particle's charging history was studied, and from the temporal dependencies of the particle Q m - ratios , the charging and discharging currents were calculated. We studied the dependence of the currents on the particle's surface voltage and developed a new method for determining the particle's size, surface potential, and electric field strength. The effects of electron and ion beam energies on the particle surface potential were measured. The energy spectrum of emitted secondary electrons was obtained and, when charging by electrons, the yield of the secondary electron emission was estimated from the voltage-dependencies of the charging current. While charging by ions there are two discharging effects: one due to secondary electrons emitted from the back wall of the quadrupole and another which is probably field emission of ions from the particle's surface. We see such emission at much lower field strengths than expected; this may imply that equilibrium surface potentials of very small (or irregularly-shaped) particles in the outer solar system might be lower than theoretical estimates predict.

Observations of dust trapping phenomena in the TRISTAN accumulation ring and a study of dust removal in a beam chamber

Using a gamma-ray detector and a television camera system for synchrotron light, high-energy bremsstrahlung and horizontal growth of the synchrotron light source were observed when sudden decrease in the electron-beam lifetime occurred due to dust trapping in the electron beam. Two types of beam current losses were found; one was a continuous beam current loss, and the other was a short-term beam current loss. High-energy bremsstrahlung at a location was observed in a short time and after that, the bremsstrahlung was not detected in spite of the occurrence of dust trapping phenomena. The fact suggests motions of the trapped dust particles in the longitudinal directions. Materials collected in the beam chamber are dust particles from ion pumps and dust particles made during the beam chamber processing for welding. Most of the collected dust particles were less than 2 mm in size and surfaces of some dust particles were melted with the electron beam. Simple analysis was carried out for the conditions necessary for a dust particle to be trapped, for motions of the trapped dust particle, and for interactions between the trapped dust particle and the electron beam. The analysis showed that a dust particle less than 3 mm in size, made of Al, can be trapped and that the trapped dust particle can move in the vertical and longitudinal directions. The analysis also suggested that a dust particle in size of about 2 mm can be continuously trapped around the electron beam without being destroyed by the electron beam. Furthermore, the analysis explained the difference between the two types of beam current losses observed in the ring. Experiments which simulate the electron beam using a Cu wire in an evacuated beam chamber show that a dust particle (less than 70 μm) is trapped sufficiently. The experiments also coincide with theory for an attractive force acting to a conducting small particle. The calculated electric field of the electron beam and the calculated electric charge of dust particles given through the photoelectric effect in the TRISTAN accumulation ring are 100 times and 104–106 times higher than those of the simulated experiments, respectively. In the ring, the attractive force caused with the average electric field and with the expected charge is 10–103 times larger than that of the simulated experiments. Therefore, a dust particle (less than 2 mm) can be trapped sufficiently. An electrostatic dust collector using an electron beam and an electrostatic force are effective in removing all of the sample dust particles in the test chamber for the simulated experiments. A method to remove trapped dust particles using electrostatic electrodes is also discussed. It is expected that such electrodes can be useful for trapped dust particles moving in a longitudinal direction.

Charge measurement of dust particles in motion

The charging of dusts or powders formed in a discontinuous flux in air is measured with a novel non-contactive method. A special ring probe was designed to measure the resultant electric charge of dust particles passing through the probe without disturbing the flow. The scope of the investigations was to verify the method proposed and to examine the influence of mass, equilibrium moisture content and velocity of motion on the electrification of PVC dusts. Experiments were carried out to study the generation of charge in the initial stage of flux formation. A mathematical model was derived to describe the response of the measuring system to the flowing resultant charge and its velocity. After the measuring system had been calibrated the empirical equation was obtained. The resultant charge (qr) and the initial rate of charge accumulation in the flux are found to be strongly dependent on the velocity of the air carrier, which causes that the dust particles are torn off from the metal surface of the feeder. The validity of the adopted measuring procedure is proved by experiments. The results obtained in terms of the mathematical model are consistent with the experimental data.

Electrification of dust produced from silicon monocrystals

Dust produced by the mechanical crushing of silicon monocrystals, doped with various concentrations of phosphorus, has been investigated. Dust electrification and conductivity measurements have been carried out. An increase in lattice defect concentration due to doping causes an increase in conductivity. The final electric charge of dust particles is the result of two opposite processes: the charge formation connected with doping of material and charge neutralization depending mainly on the surface conductivity.