An electrode microwave discharge in a static field

The effect of an external static electric field on an electrode microwave discharge in nitrogen is investigated at pressures of 1 to 5 Torr and incident power of 20 to 170 W. It is demonstrated that the current-voltage characteristics (CVC) of the discharge with respect to direct current are nonlinear; the nonlinearity defining the CVC is the plasma layer at the surface of the discharge chamber. Qualitative agreement is obtained between the measured CVC and those calculated using the self-consistent one-dimensional quasi-static model of microwave discharge in a system of electrodes with spherical symmetry. It is demonstrated that the applied dc voltage affects only slightly the discharge characteristics; however, it enables one to control flows of charged particles to the surface of the discharge chamber.     

Controlled formation of dielectric chain aggregates on material surfaces

This paper investigated the formation of chain aggregates from fine particles suspended in gas stream onto material surfaces under the action of electric field. The results showed that the shape of aggregate formed on material surface was greatly influenced by the field intensity and the surface condition of materials. In a weak electric field without corona discharge, particles tended to form clustered aggregates on a metal plate with smooth surface, but on a metal mesh and a porous alumina substrate, to form chain aggregate. On the other hand, in a corona discharge field, these surfaces were coated uniformly. Consequently, for forming chain aggregates on material surface, an electric field without corona discharge and a rough surface are necessary conditions. On rough surface, chain aggregates of dielectric particles or conductive particles grew from the protrusions of the surface and could form a rough and porous layer. When the external electric field was removed, the chain aggregates remained long time due to the Van der Waals forces. After sintered at proper temperature, the chain aggregates became fiber-like. The results indicate that the formation of chain aggregate can be controlled by electrostatic force, and sintering can be used as a method for increasing their mechanical strength.     

Large-area uniform dust-free plasma CVD

In the weak magnetic field perpendicular to the discharge electric field, both the electrons and positive ions are transported in the direction of E×B drift by the space charge electric field produced by the preceded electrons. As a result, radicals are generated uniformly outside of discharge space between the electrodes in the direction of E×B drift. On the other hand, negatively charged heavy particles such as dust particles can be removed from discharge space in the direction opposite to E×B drift of plasmas. The authors have studied the transport mechanisms of magnetized dusty plasmas and its applications for the large-area uniform a-Si:H thin film deposition in plasma CVD methods. This paper reviews the transport phenomena and the transport mechanisms of dust particles and the results of film preparation under particle-free process conditions.     

Parameters of the positive column of glow discharge with dust particles

We calculate the measured nonlocal parameters of the plasma of the positive column of direct current glow discharge in the presence of dust structures with different dust particle concentrations. The calculations are performed for typical conditions of the positive column of low-pressure glow discharge in air at which a collisional regime of maintaining discharge is achieved. The discharge plasma is described using the diffusion approximation; the flows to the surface of the dust particles are described in the orbital motion limited approximation. Calculation is carried out for micron-size particles with concentrations of up to 10¹¹ m^?3. The distribution of the dust component is assumed to be independent of the discharge parameters. Radial distributions of the plasma components and of the electric field component are obtained. The charges of dust particles for various concentrations and discharge parameters are calculated. It is demonstrated that for a certain particle concentration, the absorption efficiency of plasma particles becomes comparable with diffusion losses at the tube walls. The influence of the dust cloud on the electric field configuration at different dust particle concentrations in the cloud is analyzed. The current-voltage characteristics of the positive column of glow discharge are calculated. A higher discharge stability toward the perturbative action of dust particles at high discharge current values is demonstrated.     

Effect of inhomogeneous microwave field on the threshold of multipactor discharge on a dielectric

Multipactor discharge on a dielectric (quartz) surface has been studied in a high-Q microwave resonator excited by TE_01n mode in the 3-cm wavelength band. It is established that the discharge threshold significantly depends on the magnitude and direction of a ponderomotive force, which appears at the dielectric surface due to a gradient of the high-frequency potential. The force that repulses electrons from the surface leads to a significant increase in the threshold, whereas the attractive force decreases the threshold. Experiments confirm that a multipactor can arise in inhomogeneous electromagnetic fields in the absence of an external static field that returns emitted electrons to the dielectric surface.     

密度泛函理论研究贵金属耦合纳米团簇的静电极化率与吸收光谱

基于密度泛函理论计算了2个贵金属(Ag、Au、Cu)纳米团簇组成的团簇对的静电极化率和吸收光谱,结果表明这2个团簇之间存在强烈的静电耦合效应,其贡献主要来自于外加弱电场下团簇之间的电荷迁移和电子云的扭曲。随着团簇对间距的不断增大,静电极化率先增大后减小,存在一个极化率最大的最佳位置。在团簇对的吸收谱中,随着团簇对间距的增加,高能峰的位置和强度基本保持不变,而低能峰则不断蓝移且峰值先增大后减小,最终消失于高能峰的位置。进一步计算团簇-吡嗪和团簇-吡嗪-团簇体系的静电极化率和吸收光谱,结果发现团簇连接有机小分子后部分电子将从有机小分子向团簇迁移,使整个体系具有较大的固有极矩,在外加弱电场下,团簇与有机小分子之间的电荷迁移能力显著增强。     

Electrostatic Charging and Levitation of Helium II Drops

Liquid Helium II drops, of diameter 1 mm or less, are charged with positive helium ions and subsequently levitated by static electric fields. Stable levitation was achieved for drops of order 100–150 micrometers in diameter. The suspended drops could be translated to arbitrary positions within the levitator using additional superimposed DC electric fields, and also could be made to oscillate stably about their average positions by means of an applied time-varying electric field. A weak corona discharge was used to produce the necessary ions for levitation. A novel superfluid film flow device, developed for the controlled deployment of large charged drops, is described. Also discussed is an adjustable electric fountain that requires only a field emission tip operating at modest potentials, and works in both Helium I and Helium II.     

Numerical simulation of point-to-plane corona discharge using a Monte Carlo method

Monte Carlo simulation techniques are used to study the dynamical properties of charged particles in point-to-plane corona discharge. The numerical model includes the release of electron-ion pairs by photoionization and secondary electron emission from cathode as well as the first Townsend ionization. The simulation results of negative corona discharge in nitrogen show that electron avalanche takes place in the region of high electric field near pin electrode and the photoionization is the essential mechanism to sustain the discharge as well as electron impact ionization.     

Dielectrophoretic manipulation of particles and cells using insulating ridges in faceted prism microchannels

This paper presents a novel device for the dielectrophoretic manipulation of particles and cells. A two-level isotropic etch of a glass substrate was used to create three-dimensional ridge-like structures in micrometer-sized channels. Due to the insulating properties of glass, locally patterned regions of nonuniform electric field form near the ridges when a dc field is applied along the channel. The ridges are designed using the method of faceted prisms, such that substantially uniform fields are produced on each side of the faceted interfaces that form each ridge. The dielectrophoretic force that results from the electric field gradient near the ridges is used to affect particle motion parallel to the ridges in the absence of a bulk pressure-driven flow. Trapping and deflection of particles and continuous concentration and separation of Bacillus subtilis from a two-component sample mixture are demonstrated. The flow of B. subtilis is restricted to a selected channel of a planar, multichannel device as a result of negative dielectrophoresis arising from the presence of the insulating ridges when the applied electric field exceeds a threshold of 30 V/mm. Dielectrophoresis has a negligible impact on 200-nm-diameter polystyrene particles under the same conditions.     

Fe-Cr-Mo合金颗粒对磁流变弹性体损耗因子的影响

为改善磁流变弹性体(MRE)的阻尼性能,使用Fe-Cr-Mo合金颗粒(通过电火花方法制备得到)与硅橡胶混合制备得到了MRE样品.利用DHVTC振动测试系统测试了MRE在0~500 m T磁场范围内的动态剪切性能(激振频率为5 Hz,应变振幅为1.90%).重点研究了Fe-Cr-Mo颗粒对MRE的损耗因子的影响.结果表明,Fe-Cr-Mo合金颗粒含量达到70%时,MRE的零场损耗因子具有最大值0.24.此外,当磁场强度达到500 m T时,MRE(颗粒含量为60%)的损耗因子增加了13%.增加MRE中Fe-Cr-Mo合金颗粒含量,或者增大外磁场都会导致MRE损耗因子的提高.     

钛酸钡-明胶复合含水弹性胶体电控力学行为

将无机钛酸钡颗粒分散到含水明胶体系中,在有、无电场作用下分别胶凝得到了两种类型的复合弹性水凝胶。通过对胶体的内部颗粒分散情况分析和压缩模量的测试,研究了该胶体体系对电场的响应。结果表明,两种类型的弹性水凝胶分散相颗粒的分布有明显不同,对电场的响应程度也有很大差异。分析认为,电场作用使颗粒有序分布于连续相的胶联网络中,并形成链状结构。颗粒的有序分布使胶体的压缩模量增强,对电场作用的响应程度增大,在钛酸钡质量分数为1.5% 时胶体压缩模量出现一个极大值,并对电场响应最强。      

An experimental investigation of EGD flow of gas in a corona discharge and its influence on the motion of dispersed particles

The procedure and results of an experimental investigation of the EGD gas flow accompanying a corona discharge — the electric wind — are presented. It is shown that the motion of dispersed particles in a corona discharge is determined mainly by the electric wind.     

The giant electrorheological effect in suspensions of nanoparticles

Electrorheology (ER) denotes the control of a material's flow properties (rheology) through an electric field. We have fabricated electrorheological suspensions of coated nanoparticles that show electrically controllable liquid-solid transitions. The solid state can reach a yield strength of 130 kPa, breaking the theoretical upper bound on conventional ER static yield stress that is derived on the general assumption that the dielectric and conductive responses of the component materials are linear. In this giant electrorheological (GER) effect, the static yield stress displays near-linear dependence on the electric field, in contrast to the quadratic variation usually observed. Our GER suspensions show low current density over a wide temperature range of 10-120 degrees C, with a reversible response time of <10 ms. Finite-element simulations, based on the model of saturation surface polarization in the contact regions of neighbouring particles, yield predictions in excellent agreement with experiment.     

粉体含能材料生产与储运中的静电安全及防护

分析了静电产生的原因,阐述了粉体含能材料生产中的静电起电现象、静电的危害、静电安全性评估标准以及建立在此标准基础上的静电放电危险的评价办法,提出了粉体含能材料在生产、运输中所需要采取的静电防护措施。     

粉体含能材料生产与储运中的静电安全及防护

分析了静电产生的原因,阐述了粉体含能材料生产中的静电起电现象、静电的危害、静电安全性评估标准以及建立在此标准基础上的静电放电危险的评价办法,提出了粉体含能材料在生产、运输中所需要采取的静电防护措施。     

Experimental fluid dynamics of particles in a dielectric barrier discharge plasma-enhanced spouted bed

This study proposed the fluidized particles with dielectric barrier discharge (DBD) plasma in a slot-rectangular divergent-base spouted bed and focused on the dynamics of solid particles with the plasma irradiation. Two bed materials (Polypropylene (PP) particles and Polyamide (PA) particles) with same diameter (3 mm) were fluidized in this study. Fluidization parameters included gas velocity (7.4–14.9 m/s), particle amount (100–500), and plasma parameter (apply voltage, 0 and 7 kV) as the applied voltage were investigated here. Particle velocity profiles were analyzed through the methods of particle image velocimetry (PIV) and particle tracking velocimetry (PTV). Results show that the particle velocity was increased with the plasma irradiation, mainly by the enhancement in the vertical direction. The location of the highest particle velocity area related to the fluidization behavior of particles. With the increase of superficial gas velocity, the location of the highest particle velocity area raised along the central line but not reached the top of the solid bed. While the electron temperature of Ar plasma decreased with the addition of particles. Two electric fields (external electric field and surface charge electric field) presenting in the system were assumed to give the reason for the changes of the particle fluid dynamics.     

栅极偏压对电光聚合物电晕极化的影响

实验研究了带栅极的电晕放电极化系统的性能。比较了不同栅极偏压下的电晕放电特性。分析了极化电压、栅极偏压和极化电场分布等相关问题。实验结果显示,栅极偏置电晕放电极化系统的电光聚合物极化效果较无栅极时好得多。     

Electrostatic Evaluation of a Unipolar Diffusion and Field Charger of Aerosol Particles by a Corona Discharge

This article presents a unipolar diffusion and field charger by corona discharge is presented and electrostatically evaluated for charging aerosol particles. The electrostatic characteristics of the charger were investigated with an electrometer by measuring the ion number concentrations corresponding to the discharge and charging currents. The discharge and charging currents, and ion number concentration in the discharge and charging zones of the charger, increased with corona voltage. The magnitudes of the ion number concentration for positive and negative coronas in the discharge zone ranged from 1.34 × 10¹³ to 1.84 × 10¹⁵ ions/m³ and 7.34 × 10¹³ to 2.64 × 10¹⁵ ions/m³, respectively. For the charging zone, the ion number concentrations for positive and negative coronas ranged from 2.95 × 10¹³ to 1.52 × 10¹⁴ ions/m³ and 2.06 × 10¹³ to 1.47 × 10¹⁴ ions/m³, respectively. To predict the behavior of the electric field strength and lines in the discharge and charging zones of the charger, the electric field strength and distribution of the charger in the discharge and charging zones were calculated by a commercial computational fluid dynamics software package. Numerical calculation results of electric field distribution and lines through the inner electrode showed good agreement with experimental results. Also, the mean charge per particle for particle diameters were in the range of 0.01 to 50 µm for various operating conditions of the charger was theoretically evaluated. For both diffusion and field charging, lower aerosol flow rate and higher corona voltage resulted in an increase in the mean charge per particle within the charger. This simple charger proved to be particularly useful in diffusion and field charging of aerosol particles in particulate matter detector instruments for measuring PM10 and PM2.5 concentration.     

Plasma-assisted ignition and deflagration-to-detonation transition

Non-equilibrium plasma demonstrates great potential to control ultra-lean, ultra-fast, low-temperature flames and to become an extremely promising technology for a wide range of applications, including aviation gas turbine engines, piston engines, RAMjets, SCRAMjets and detonation initiation for pulsed detonation engines. The analysis of discharge processes shows that the discharge energy can be deposited into the desired internal degrees of freedom of molecules when varying the reduced electric field, E/n, at which the discharge is maintained. The amount of deposited energy is controlled by other discharge and gas parameters, including electric pulse duration, discharge current, gas number density, gas temperature, etc. As a rule, the dominant mechanism of the effect of non-equilibrium plasma on ignition and combustion is associated with the generation of active particles in the discharge plasma. For plasma-assisted ignition and combustion in mixtures containing air, the most promising active species are O atoms and, to a smaller extent, some other neutral atoms and radicals. These active particles are efficiently produced in high-voltage, nanosecond, pulse discharges owing to electron-impact dissociation of molecules and electron-impact excitation of N(2) electronic states, followed by collisional quenching of these states to dissociate the molecules. Mechanisms of deflagration-to-detonation transition (DDT) initiation by non-equilibrium plasma were analysed. For longitudinal discharges with a high power density in a plasma channel, two fast DDT mechanisms have been observed. When initiated by a spark or a transient discharge, the mixture ignited simultaneously over the volume of the discharge channel, producing a shock wave with a Mach number greater than 2 and a flame. A gradient mechanism of DDT similar to that proposed by Zeldovich has been observed experimentally under streamer initiation.     

Enhancement of HHG yield

A static electric field periodically distributed in space controls and enhances the yield in high harmonic generation. The method is relatively simple to implement and allows tuning from the extreme-ultraviolet to soft X-ray. The radiation yield is selectively enhanced due to symmetry breaking induced by a static electric field on the interaction between the driving laser and the medium. The enhanced spectral region is tuned by varying the periodicity of the static electric field. Simulations predict an increase of more than two orders of magnitude for harmonics in the water window spectral range.