The Electrostatic Trapping of an Intense Relativistic Electron Beam in a Magnetic Mirror

Observations of rapid axial oscillations of an intense relativistic electron beam in a magnetic mirror are reported. The mirror field primarily provides radial confinement of the relativistic electrons. The axial confinement was achieved by placing thin aluminized mylar foils at the conjugate mirror field maxima. The region between these foils was filled with a few Torr air to provide a beam induced plasma for charge and current neutralization. The regions outside these foils were maintained at ~10-4 Torr. One foil formed the anode of a space-charge limited relativistic electron diode which launched the beam into the mirror. When the beam passed through the second foil it was no longer charge neutralized. In a manner quite similar to the anode foil oscillations observed by others, a space-charge limited electrostatic well was established which stopped the electrons and re-accelerated them through the foil-thereby reflecting the beam. When the reflected electrons re-entered the diode, they were once again "electrostatically" reflected. This process continued until the oscillating beam was either lost through the "virtual cathodes" outside the foils, dissipated in the drift region or quenched in the diode plasma after gap closure.     

Ion track etching revisited: II. Electronic properties of aged tracks in polymers

We compile here electronic ion track etching effects, such as capacitive-type currents, current spike emission, phase shift, rectification and background currents that eventually emerge upon application of sinusoidal alternating voltages across thin, aged swift heavy ion-irradiated polymer foils during etching. Both capacitive-type currents and current spike emission occur as long as obstacles still prevent a smooth continuous charge carrier passage across the foils. In the case of sufficiently high applied electric fields, these obstacles are overcome by spike emission. These effects vanish upon etchant breakthrough. Subsequent transmitted currents are usually of Ohmic type, but shortly after breakthrough (during the track’ core etching) often still exhibit deviations such as strong positive phase shifts. They stem from very slow charge carrier mobility across the etched ion tracks due to retarding trapping/detrapping processes. Upon etching the track’s penumbra, one occasionally observes a split-up into two transmitted current components, one with positive and another one with negative phase shifts. Usually, these phase shifts vanish when bulk etching starts. Current rectification upon track etching is a very frequent phenomenon. Rectification uses to inverse when core etching ends and penumbra etching begins. When the latter ends, rectification largely vanishes. Occasionally, some residual rectification remains which we attribute to the aged polymeric bulk itself. Last not least, we still consider background currents which often emerge transiently during track etching. We could assign them clearly to differences in the electrochemical potential of the liquids on both sides of the etched polymer foils. Transient relaxation effects during the track etching cause their eventually chaotic behaviour.     

In-situ multi-information measurement system for preparing gallium nitride photocathode

We introduce the first domestic in-situ multi-information measurement system for a gallium nitride (GaN) photo- cathode. This system can successfully fulfill heat cleaning and activation for GaN in an ultrahigh vacuum environment and produce a GaN photocathode with a negative electron affinity (NEA) status. Information including the heat clean- ing temperature, vacuum degree, photocurrent, electric current of cesium source, oxygen source, and the most important information about the spectral response, or equivalently, the quantum efficiency (QE) can be obtained during prepa- ration. The preparation of a GaN photocathode with this system indicates that the optimal heating temperature in a vacuum is about 700 C. We also develop a method of quickly evaluating the atomically clean surface with the vacuum degree versus wavelength curve to prevent possible secondary contamination when the atomic level cleaning surface is tested with X-ray photoelectron spectroscopy. The photocurrent shows a quick enhancement when the current ratio between the cesium source and oxygen source is 1.025. The spectral response of the GaN photocathode is flat in a wavelength range from 240 nm to 365 nm, and an abrupt decline is observed at 365 nm, which demonstrates that with the in-situ multi-information measurement system the NEA GaN photocathode can be successfully prepared.     

声脉冲法空间电荷测量系统的研究

气体中空间电荷的分布与电晕放电的机理紧密相关, 获取电晕放电过程中空间电荷分布对深入研究电晕放电起始、自持过程有着重要作用, 但是如何准确获得电晕放电过程中的空间电荷分布一直是国际上尚未解决的难题. 本文基于声脉冲法提出一种电场信号解耦算法, 推导了空间电荷在声场中被调制产生的电场信号与声脉冲信号和空间电荷密度之间的数值关系, 讨论了不同测量情况下声发射系统的设计要求; 搭建了一套可用于实时测量针板电极电晕放电空间电荷分布的非接触式测量系统, 该系统主要包括声脉冲发生模块、空间电荷模块及电场信号解耦算法模块. 运用该系统实现了声脉冲激发作用下电场信号的测量, 通过提出的电场信号解耦算法得到了空间电荷密度, 对其测量结果与电晕电流法测量结果进行比较, 验证了电场信号解耦算法的有效性. 该算法可以应用于空间电荷一维、二维和三维测量系统中.     

Corona-discharge-based neutralization of charged granular insulating materials in contact with an electrode of opposite polarity

Charge neutralization is a key operation in many electrostatic processes. A wide-range of charge neutralizers have already been developed for various applications: eliminate shock and ignition hazards, avoid electrostatic discharges that might affect the operation of electronic equipment, reduce electrostatic adhesion forces that might stick granular materials in pneumatic conveyors, and so on. The aim of the present paper is to evaluate several methods of charge neutralization for charged granular insulating materials spread on an electrode energized from a voltage source of opposite polarity, a situation encountered – for instance – in two-metallic-belt tribo-aero-electrostatic separators, and which is not covered by commercially-available solutions. Three corona-discharge-based charge neutralization systems are studied: (i) DC-biased AC voltage applied to a corona dual-type electrode; (ii) DC-biased AC voltage applied to a triode-type electrode system; (iii) DC voltage applied to a corona dual-type electrode. The charged samples of polycarbonate granules are obtained at the outlet of a tribo-aero-electrostatic separator. The electric charge per mass ratio of each sample is measured before and after neutralization. The third of the above-mentioned charge neutralization solutions seems to be the most effective solution, but it requires an appropriate adjustment of the DC voltage applied to the corona dual-type electrode.     

充空气的同轴慢波结构高功率微波器件粒子模拟

粒子模拟了电子碰撞空气产生的等离子体对同轴慢波结构高功率微波器件的影响,并且在充空气条件下对器件结构参数进行了进一步优化。模拟表明,气压越高,产生的二极管电流越大,二极管电压越低,频率越低。等离子体离子对电子束的空间电荷中和及等离子体电子对微波的能量吸收共同影响输出微波功率的大小。在一定的气压范围内,提高气压能够提高输出功率,此时等离子体离子对电子束的空间电荷中和起主导作用。气压高于一定值时,所产生的等离子体电子强烈吸收微波,输出功率迅速下降,甚至引起脉冲缩短。此外,由于等离子体的存在,器件最佳相互作用区长度以及最优端面反射系数均有可能发生改变。最后还对慢波结构周期数以及漂移段长度等进行了研究,优化的器件内、外导体周期数为11和8.5,慢波结构前端以及内外慢波结构末端分别接4, 17和2 mm的漂移段,在气压4 Pa下获得了1.64 GW的输出功率,效率39%。     

Efficient charge neutralization with an ac corona ionizer

This paper discusses the problem of obtaining effective charge neutralization by an ac corona ionizer with airflow. The motion of ions and the neutralization of a charged object for different discharge frequencies and airflow velocities are investigated by a computer fluid model for positive and negative ions. The results of the investigation show that, in the region of ion transport, the quasi-neutralized charge distribution self-generated by positive and negative ions during charge neutralization can effectively transport the ions themselves from an ionizer to a charged object and significantly reduce both the unwanted fluctuation and dc offset in the potential of the object at a steady state, resulting in efficient and precise charge neutralization. Since the quasi-neutralization greatly depends on the relationship between the discharge frequency and airflow velocity, the control of the relationship may lead to better neutralization with an air-blowing ac ionizer.     

Charge state dependent energy deposition by ion impact

We report on a measurement of craters in thin dielectric films formed by Xe(Q+) (26 ≤ Q ≤ 44) projectiles. Tunnel junction devices with ion-irradiated barriers were used to amplify the effect of charge-dependent cratering through the exponential dependence of tunneling conductance on barrier thickness. Electrical conductance of a crater σ(c)(Q) increased by 4 orders of magnitude (7.9 × 10(-4) μS to 6.1 μS) as Q increased, corresponding to crater depths ranging from 2 to 11 ?. By employing a heated spike model, we determine that the energy required to produce the craters spans from 8 to 25 keV over the investigated charge states. Considering energy from preequilibrium nuclear and electronic stopping as well as neutralization, we find that at least (27 ± 2)% of available projectile neutralization energy is deposited into the thin film during impact.     

导电箔对于相对论环形束的约束作用分析及其对束流群聚过程影响的初步实验结果

分析导电箔上的镜像电荷对环形束的约束作用,给出了可用于设计选择聚焦环形束的导电箔几何尺寸的计算结果。利用已有的X波段相对论速调管(RKA)进行了初步的镜像电荷聚焦RKA的实验。虽然实验中的导电箔对电子束的通过率只有0.88,但结果表明导电箔对RKA的束流有一定聚焦作用,不影响束流群聚过程。     

Non-contact in-situ pulsed electro acoustic method for the analysis of charge transport in irradiated space-used polymers

The characterization of dielectric materials in space environment requires to understand and predict their electric behaviour, taking into account ionisation, and ageing effect (through electron or UV radiation, thermal cycling, …)For this purpose, new methods have been developed for the characterisation and qualification of space materials and satellite structure. These studies led initially to the development of dedicated facilities for the simulation of representative irradiation conditions. This work is focused on a new non-disturbing technique for the measurement of charge distribution within space irradiated polymers. This technique named PEA (Pulsed Electro-Acoustic) has been implemented in the irradiation facility for in-situ and real time measurement during irradiation and relaxation of polymer materials. Implementation and validation of this technique are presented and discussed in this paper.     

充空气的同轴慢波结构高功率微波器件粒子模拟

 粒子模拟了电子碰撞空气产生的等离子体对同轴慢波结构高功率微波器件的影响,并且在充空气条件下对器件结构参数进行了进一步优化。模拟表明,气压越高,产生的二极管电流越大,二极管电压越低,频率越低。等离子体离子对电子束的空间电荷中和及等离子体电子对微波的能量吸收共同影响输出微波功率的大小。在一定的气压范围内,提高气压能够提高输出功率,此时等离子体离子对电子束的空间电荷中和起主导作用。气压高于一定值时,所产生的等离子体电子强烈吸收微波,输出功率迅速下降,甚至引起脉冲缩短。此外,由于等离子体的存在,器件最佳相互作用区长度以及最优端面反射系数均有可能发生改变。最后还对慢波结构周期数以及漂移段长度等进行了研究,优化的器件内、外导体周期数为11和8.5,慢波结构前端以及内外慢波结构末端分别接4, 17和2 mm的漂移段,在气压4 Pa下获得了1.64 GW的输出功率,效率39%。     

Beyond Millikan: the dynamics of charging events on individual colloidal particles

By measuring the stable charge on oil drops in air, Millikan demonstrated the discrete nature of electric charge. We extend his approach to the charge on solid-liquid interfaces, and focus on the dynamics of the discrete fluctuations. Our measurements are accurate and fast enough to observe changes of one elementary charge. Experiments over thousands of seconds yield information about the fast dynamics of electrochemical reactions, relevant for physicochemical and biological systems. As an example, we study (dis)charging processes on colloidal particles in a nonpolar liquid.     

Quantum antidot as an electrometer:Observation of fractional charge

In experiments on resonant tunneling through a quantum antidot in the quantum Hall (QH) regime, we observe periodic conductance peaks both versus magnetic field and a global gate voltage, i.e., electric field. Each conductance peak can be attributed to tunneling through a quantized antidot-bound state. The fact that the variation of the uniform electric field produces conductance peaks implies that the deficiency of the electrical charge on the antidot is quantized in units of charge of quasiparticles of surrounding QH condensate. The period in magnetic field gives the effective area of the antidot state through which tunneling occurs, the period in electric field (obtained from the global gate voltage) then constitutes a direct measurement of the charge of the tunneling particles. We obtain electron charge C in the integer QH regime, and quasiparticle charge C for the QH state.     

Detection of positive and negative ions in a wire ionization counter filled with atmospheric air

The physical processes occurring during the detection of individual ions in a wire counter filled with atmospheric air are studied, and the amplitude distribution of electric pulses is measured. It is shown that a positive ion is detected due to electron emission from the surface of a negatively charged wire, whereas a negative ion is detected due to electron detachment near a positively charged wire. The secondary processes accompanying the neutralization of positive ions at a negatively charged external electrode and negatively charged wire are considered. It is established that, in contrast to standard proportional counters, these secondary processes result in an increase in the number of electric pulses rather than in an increase in the electric pulse amplitude. The wire counter allows the detection of both ions produced inside the detector and ions injected into the detector from the ambient air. Possible applications of air-filled wire detectors are described.     

An integral approach to considering the evolution of a microwave streamer

We present a model of a microwave streamer based on analytical relations that allows its evolution to be described both during its elongation along the external electric field and after its stop. The equations for the electric field amplitude at the streamer center, the equations that describe the dynamics of the longitudinal and transverse sizes, and the equations of plasma chemical kinetics are self-consistently solved in terms of this model. Comparison with numerical 2D simulations of the electrostatic stage in air is made. We derive simple analytical relations that allow the power released in a plasma channel to be estimated on the fly. Almost the entire energy contribution is shown to be made after the termination of the streamer elongation.     

热氧化铜箔中的起皱和CuO纳米线的生长机

在500 oC大气条件下热氧化0.5 mm厚的铜箔0.5～10 h有起皱现象,且皱的大小随氧化时间的增加而增大,在皱的侧面和顶部均有生长CuO纳米线,皱侧面生长纳米线的长度比皱顶部的纳米线的长,密度也高;CuO纳米线的生长方向垂直于纳米线的生长表面. 通过计算波动阶段中皱内部的局部电场,发现皱的侧面和顶部的电场强度的数值相差很小,表明在CuO纳米线生长过程中驱动铜离子扩散的主要驱动力不是局部的电场力而是内应力.     

风道清洗机器人系统的设计优化与工程测试

中央空调风道的定期清洗作用很大,既可以改善室内空气质量,又能够实现节能。本文介绍了一种专门针对中央空调风道清洗的机器人系统,对其四大组成部分进行了详细介绍;在分析该系统技术原理与性能参数的基础之上,对风道清洗机器人系统进行系统结构与部件形式上的优化,提出了“闭式循环”集尘方式,并对刷头形状做了改进;最后基于具体工程实例的测试结果,对清洗前后管壁积尘量、管道风速进行对比,分析该系统在改善空调系统卫生状况与气流组织状况方面的显著作用。     

大调制度下光折变运动光栅的微扰分析

利用“跳跃模型”讨论了大调制度下光折变材料对运动干涉条纹的非静态记录过程，给出了描述运动干涉条纹非静态记录时电荷密度波前三阶分量振幅的微分方程，以及前三阶空间电荷场的解析表达式.讨论了前三阶空间电荷场振幅改变量对干涉条纹运动速度的依赖关系，若扩散场不为零但较小时，施加较小的外电场能够实现对空间电荷场高阶分量选择性地增强.若扩散场较大(大于外加电场)，则不能实现对空间电荷场高阶分量选择性地增强. 关键词：     

Exact partial solutions for the surface dynamics of a dielectric liquid with a charged surface in the gravitational field

We study the evolution of instability in the boundary of a perfect dielectric liquid with a free surface charge in an external electric field. Conformal variables are used to find exact partial solutions to the equations of motion for the case when the charge completely shields the field above the liquid, the electrostatic and gravitational forces being taken into account. The solutions describe the development of instability of the initially planar boundary until sharp dimples are formed on it.     

Electric discharge in air in a deeply subcritical field of a quasi-optical microwave beam

We describe the results of experiments on initiation of an electric discharge in air in a quasi-optical microwave beam by an electromagnetic vibrator fixed above the screen. This method for initiating the electrical breakdown makes it possible to obtain a discharge at a level of the electric field component in the microwave, which two orders of magnitude lower than the minimal critical field of the electrodeless breakdown of air. In our experiments, the threshold value of the air pressure determining the low- and high-temperature forms of the microwave discharge are determined depending on the field level.