Hybrid computer simulations: electrical charging of dust particles in low-temperature plasma

This paper is focused on the study of the electrical charging process of micron-sized particles immersed into low-temperature argon plasma by the methods of computer modelling. The hybrid computer simulations are performed for a set of particles with the radius up to in order to determine the dependence of the electric charge on the surface of the particulate on its radius. This dependence seems to be linear. The distribution of the electric potential in the vicinity of the particulate is obtained from the fluid model. Afterwards, the non self-consistent particle simulation is performed in order to determine both the reaction rates and the electric charge on the surface of the particulate. The most important collision processes of charged particles in plasma and the appropriate dependence of the collision cross-section on the particle energy are considered (elastic scattering of electrons on neutrals, excitation of neutrals into all important energetic states, ionisation of Argon atoms by fast electrons, elastic scattering of positively charged ions etc.). The presented algorithm provides an effective way, how the key quantity in dusty plasma physics – electric charge on the surface of the particulate – can be determined.     

Optimal control of a charge qubit in a double quantum dot with a Coulomb impurity

We study the efficiency of modulated external electric pulses to produce efficient and fast charge localization transitions in a two-electron double quantum dot. We use a configuration interaction method to calculate the electronic structure of a quantum dot model within the effective mass approximation. The interaction with the electric field is considered within the dipole approximation and optimal control theory is applied to design high-fidelity ultrafast pulses in pristine samples. We assessed the influence of the presence of Coulomb charged impurities on the efficiency and speed of the pulses. A protocol based on a two-step optimization is proposed for preserving both advantages of the original pulse. The processes affecting the charge localization is explained from the dipole transitions of the lowest lying two-electron states, as described by a discrete model with an effective electron-electron interaction.     

Generation of unipolar pulses in nonlinear media

Methods recently proposed for generating unipolar pulses in nonlinear media in terahertz and optical electromagnetic ranges are reviewed. Such pulses have nonzero “electric area” (time integral of the field strength over the entire duration of a pulse) and, correspondingly, a significant component of the field with zero frequency, thus exhibiting quasistatic properties. Effective generation of unipolar pulses would allow, e.g., transferring mechanical momentum to charged particles and, thereby, controlling the motion of wave packets of matter, which can be useful for compact accelerators of charged particles and for other applications.     

Dynamics of induction charging for multiple particle agglomerations with a thin conducting surface layer

In electrostatic applications, particles are typically stacked in an arbitrary array. In this paper, multiple particle agglomerations with a finite volume conductivity, surface conductivity and permittivity have been simulated. Upon exposure to the electric field, electric shielding can occur due to the proximity of other particles, which greatly reduces the maximum accumulated charge and affects the charging time. All results have been obtained using the COMSOL commercial software. The simulation results show that shielding the electric field from a given particle reduces its saturation charge and the rate of charge accumulation was mainly affected by the volume and surface conductivities.     

Increase in the molecular component of the adhesive pressure in polymer composites induced by electric charge

The effect of electric charge, present at a glass fiber–polymer interface during the composite material formation, on the adhesive pressure between the components was studied. Additional electric charge was delivered to the interface by means of the deposition of charged polymer particles onto the fiber surface from a fluidized bed in an electric field. The adhesive pressure was calculated using the results of the variational mechanics analysis by Scheer and Nairn from the data obtained with a single fiber microbond test. Our experiments showed that the adhesive pressure increased by 15–20% in the case of charged polymer matrices. This can be attributed to both intensification of van der Waals forces due to extra interfacial pressure and, for polar polymers, the increase of the surface concentration of local adhesive bonds. The mechanical and kinetic models have been proposed to describe the observed behavior of the adhesive pressure; theoretical curves for the adhesive pressure as a function of the time and temperature of the contact formation, including the effect of electric factors, have been obtained. From the kinetic model, the activation energies for the process of adhesive contact formation were determined. The effect of acceleration of adhesive bonding in the presence of electric charge can be explained in terms of a decrease of the activation energy for local bond formation in an electric field.     

Surface effects in Debye screening

A thermodynamic system of equally charged, plus and minus, classical particles constrained to move in a (spherical) ball is studied in a region of parameters in which Debye screening takes place. The activities of the two charge species are not taken as necessarily equal. We must deal with two physically interesting surface effects, the formation of a surface charge layer, and long range forces reaching around the outside of the spherical volume. This is an example in as much as 1) general charge species are not considered, 2) the volume is taken as a ball, 3) a simple choice for the short range forces (necessary for stability) is taken. We feel the present system is general enough to exhibit all the interesting physical phenomena, and that the methods used are capable of extension to much more general systems. The techniques herein involve use of the sine-Gordon transformation to get a continuum field problem which in turn is studied via a multi-phase cluster expansion. This route follows other recent rigorous treatments of Debye screening.This work was supported in part by the National Science Foundation under Grants No. PHY 83-01011 and PHY 81-16101 A03     

半绝缘GaAs光电导开关产生太赫兹波电场屏蔽效应的二维Monte Carlo模拟

利用Ensemble-Monte Carlo模拟方法，对不同实验条件下半绝缘GaAs(SI-GaAs)光电导开关作为偶极辐射天线在辐射太赫兹电磁波(太赫兹波)中体内电场的分布以及空间电荷屏蔽效应对太赫兹波辐射的影响进行了模拟.载流子的时域空间电场分布表明:用高能量激光脉冲触发低压偏置的GaAs开关，空间电荷屏蔽是限制太赫兹波辐射功率的一个重要因素，并且空间电荷屏蔽能够引起太赫兹波呈现双极性.当高能量飞秒激光脉冲以全电极间隙触发大孔径光电导天线时，空间电荷电场屏蔽效应对太赫兹波的影响不大. 关键词： 光电导开关 Ensemble-Monte Carlo模拟 辐射场屏蔽 空间电荷屏蔽     

Electric charge and field in the meniscus of a dielectric fluid

Using the conformal mapping method, we calculate the electric field at the tip of a high-voltage electrode mounted in the injector of fluid particles. The space charge of the dielectric fluid charged from the high-voltage electrode of the injector of the fluid charged particles is determined. We present the results of simulation of the charge and field in the meniscus for VM-1vacuum oil.     

Mass Transfer in Free Convection Developing in a Magnetic Field

The interaction of a charged hydrated particle with an external magnetic field is analyzed under conditions of diffusion and convective mass transfer. A model of forming local space charge regions in the bulk of a solution is suggested. The model is used to study the feasibility of changing the velocity and redistribution of charged particles in an aqueous medium. The results of theoretical calculations are tested experimentally by quantitative estimation of the rate of the convective liquid flow developed in crossed electric and magnetic fields.     

Attraction mechanism of like-charged aerosol particles in a moving conductive medium

We analyze the structure of the space electric charge that appears in the vicinity of a charged dust particle in a moving conductive medium. We show that when the conduction currents play a major role, the screening space charge is concentrated in the form of a thin wake behind the dust particle, while the total Coulomb field forms a dipole structure and serves as an attractive center for other particles with charges of the same sign. We consider the pairing conditions for such particles. Including the polarization contribution from the dust component to the permittivity radically changes the field structure when the dust particle concentration approaches the dissipative instability threshold. In this case, the zone of attraction of like-charged dust particles expands sharply. Estimates suggest that the effects under consideration can govern the formation of regular structures in a moving dusty plasma at fairly high pressures, P > 0.1–1 mbar.     

On the determination of vertical profiles of temperature, charge concentration, and potential in the surface layer of an aircraft

A “3/2 law” law has been established for the vertical charge concentration profile (i.e., the particle concentration is proportional to temperature to a power of 3/2). The expression is derived for the electric field potential produced by charged particles at the upper boundary of the viscous sublayer, as well as for the density current produced by charged particles moving in the air flow streamlining an aircraft. It is shown that all these parameters increase with altitude and assume maximum values at the turbulent layer surface.     

Some effects of the electrostatic interaction of water drops in the atmosphere

The electric field at the surface of two conducting spherical charged particles and their interaction force are calculated. It is shown that as particles carrying like charge approach each other, the force changes sign and becomes attractive. The case where the charge on each particle varies as the square of its radius is an exception (repulsion at any distance between the particles). Self-similar asymptotic solutions for the interaction force and energy are found for particles of identical size. For a pair of charged water drops falling simultaneously in the atmosphere, a numerical simulation shows that a drop formed by coalescence of the pair may be subject to the Rayleigh instability. Zh. Tekh. Fiz. 69, 12–17 (December 1999)     

Tunneling of Charged and Magnetized Fermions from the Kerr-Newman-Ads Black Hole with Magnetic Charges

Tunneling of charged and magnetized Dirac particles from the Kerr-Newman-Ads black hole with magnetic charges is discussed in this paper. Owing to the electric and magnetic fields would couple with gravity field, we introduce the Dirac equation of charged and magnetized particles. Then by redefining the equivalent charge and gauge potential corresponding to the source with electric and magnetic charges, we discuss this tunneling once and obtain the same Hawking temperature. Both results show that the fermions tunneling formalism also come into existence in the charged and magnetized background space time.     

Screened electrostatics of charged particles on a water droplet

We study the electrostatic properties of charged particles trapped at an interface in a water-in-oil microemulsion. The electrostatic potential and the counterion distribution in the water droplet are given in terms of the ratio of the Debye screening length κ^-1 and the droplet radius R. In the limit R→∞ we recover the well-known results for a flat interface. Finite-size corrections are obtained in terms of the small parameter 1/κR. Part of the counterions spread along the interface and form a charged layer of one Debye length thickness. In particular, there is a uniform surface charge contribution. We derive explicit expressions for the electric field, the mobile charge density, and the charge-induced pressure on the interface.     

Ionic plasma oscillations in superionic conductors

Some superionic conductors behave as if their charge was carried by nearly free charged particles. If this is the case, these free particles should undergo plasma oscillations. The plasma oscillations may already have been observed in superionic AgI and CuI. Similar oscillations might also be observable in ionic liquids such as melted AgI.     

Electromagnetic scattering of charged particles in a strong wind-blown sand electric field

Some field experimental results have shown that the moving sands or dust aerosols in nature are usually electrified,and those charged particles also produce a strong electric field in air, which is named as wind-blown sand electric field.Some scholars have pointed out that the net charge on the particle significantly enhances its electromagnetic(EM) extinction properties, but up to now, there is no conclusive research on the effect of the environmental electric field. Based on the extended Mie theory, the effect of the electric field in a sandstorm on the EM attenuation properties of the charged larger dust particle is studied. The numerical results indicate that the environmental electric field also has a great influence on the particle's optical properties, and the stronger the electric field, the bigger the effect. In addition, the charged angle, the charge density, and the particle radius all have a specific impact on the charged particle's optical properties.     

Tunneling of Charged and Magnetized Fermions from the Reissner-Nordström Black Hole with Magnetic Charges

The Kerner-Mann fermions tunneling framework is extended to the spin particles with electric and magnetic charges in this paper. We rewrite the electromagnetic field tensor and the Lagrangian of the field corresponding to the source with electric and magnetic charges to redefine an equivalent charge. We only consider the case that the ratio of the electric charge and magnetic charge of the emission is constant and equal to the source. The result shows that when the energy conservation together with the electric charge and magnetic charge conservations are taken into account in the dynamical background space time, the emission rate agrees with the underlying unitary theory and the actual radiation spectrum of charged and magnetized fermions also derivates from the pure thermal one.     

Characterization of particulates accompanying laser ablation of pressed polytetrafluorethylene (PTFE) targets

We present observations of sub-micron- to micron-sized particles generated by high fluence (≈2 J/cm²) 248-nm laser ablation of pressed polytetrafluorethylene (PTFE) targets in air at atmospheric pressure. The original target material was hydrostatically compressed ≈7 μm PTFE powder, sintered at 275 °C. Collected ejecta due to laser irradiation consists of four basic particle morphologies ranging from small particles 50–200 nm in diameter to larger particles ≈10 μm in diameter. Many particles formed in air carry electric charge. Using charged electrodes we are able to collect charged particles to determine relative numbers of ± charge. We observe roughly equal numbers of positively and negatively charged particles except for the largest particles which were predominantly negative. For a range of particle sizes we are able to measure the sign and magnitude of this charge with a Millikan-oil-drop technique and determine surface charge densities. The implications of these observations with respect to pulsed laser deposition of PTFE thin films and coatings are discussed. Received: 15 January 1999 / Accepted: 18 January 1999 / Published online: 7 April 1999     

Discharges and mechanoelectrical phenomena in charged glasses

Conclusions In high-resistance solid dielectrics (with resistances of 10¹² · cm or higher, when they are irradiated with electron beams, spontaneous electric discharges are observed while the irradiation is occurring. The discharges occur at defects in the surface and develop in the layer within which the charged particles are distributed.When the charged particles are distributed in the surface or near-surface layer of the dielectric, the discharge may be initiated close to the charged surface by a grounded metal needle, even some time after the irradiation. After long storage and self-dis charge of the surface layer of the irradiated dielectric or compensation of the surface charge, discharge of the charge stored in the depth of the dielectric can occur by scratching the surface or pricking it with a needle. When the charge lies deep inside the dielectric, a brush discharge occurs when a strong shock is applied to the surface of the dielectric using a grounded needle.In all the above cases initiation of an electric discharge in the solid dielectric occurred by mechanoelectrical phenomena of direct conversion of mechanical energy into electrical energy with a high field strength. These phenomena occur in solid dielectrics with a defect structure.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 40–46, February, 1977.