相对论电子束虚阴极静电振荡的粒子模拟

本文运用有限大小粒子模型,用等离子体粒子模拟方法,对相对论电子束的虚阴极振荡作了一维静电粒子模拟。结果表明,在注入电流小于空间电荷极限电流时,电子束能稳定传输并能全部通过。当注入电流超过空间电荷极限电流时,传输是不稳定的,将有部分电子反射,部分通过。空间电荷形成的虚阴极的位置和电势周期性地振荡。电流越大,虚阴极位置越靠近注入面且变化范围越小,虚阴极电势越低且振幅越大,振荡频率越高且大于电子束等离子体频率。     

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.     

TWO-DIMENSIONAL NUMERICAL SIMULATION OF LOW FREQUENCY OSCILLATIONS OF SPACE CHARGE AND POTENTIAL IN THE GYROTRON ADIABATIC TRAP

The development of oscillations of the space charge and potential in the adiabatic trap of a gyrotron between the cathode and the cavity is studied numerically. The PIC method is applied, with the real two-dimensional distributions of the electric and magnetic fields taken into account. Secondary emission is included into the numerical model, as well as such factors as the electron beam space charge, thermal velocities of electrons, and emitter roughness. The value of the trapped space charge as a function of time is calculated. Time dependences of the potential in various cross-sections of the formation system are traced. The amplitudes of its variable component have been found and then the corresponding frequency spectra have been calculated. The process of cathode bombardment is investigated. The energy distribution and time dependence of the current in the electron beam coming to the operating space are found. Some ways to reduce the oscillations of the potential and the space charge are discussed.     

Electrostatic potential and field near the boundary between space charge and no charge regions within a cylindrical pipe

In electronic industries, a corona ionizer is widely used for the elimination of electrostatic charge on the material. Although the high frequency AC ionizer proved the effectiveness of its performance, the corona ions must be sent through a metal pipe to reach targeting area. In order to analyze the behavior of ions in elimination process, the potential and electric field within a pipe must be known. Since the potential and field distribution near the boundary between space charge and no charge regions are extremely important, the analytical solution for this problem was sought by using Bessel functions. Analytical solution showed that even in no charge region, there exists potential distribution within a pipe. Numerical calculation of electric field on the inner pipe surface indicated useful information to estimate the charge density in the pipe. Furthermore, some mathematical formulae were obtained by using Bessel functions.     

空间电荷效应对热场致发射中诺廷汉效应的影响

热场致发射阴极所产生的强流电子束具有很强的空间电荷效应,为研究该效应对热场致发射过程中诺廷汉（Nottingham）效应的影响机理,在理论分析的基础上,用数值方法研究了不同逸出功和多个外加电场条件下考虑空间电荷效应对诺廷汉效应结果的影响,并与不考虑空间电荷效应时的情形进行了对比. 结果表明：空间电荷效应的强弱会显著影响到阴极表面的稳态电场,进而对诺廷汉效应产生不可忽略的影响;当逸出功在3.0–4.52 eV、外加电场在3×10⁹–9×10⁹ V/m范围内时,考虑空间电荷效应的影响后,热场致发射电子所带走的平均能量较不考虑空间电荷效应时增加0–2.5 eV,且温度越高或外加电场越大时,该增加值越大;考虑空间电荷效应对诺廷汉效应的影响后,热场致发射电子从阴极带走的平均能量随外加电场的增加呈非线性下降规律;当阴极表面温度较高时,诺廷汉效应中的冷却效应随二极管间隙距离的变大而增强. 关键词： 热场致发射 诺廷汉效应 空间电荷效应 阴极表面电场     

轴对称真空二极管空间电荷限制流

基于ArcPIC代码采用PIC-MCC方法,模拟研究了轴对称真空二极管放电时电子密度和阴极表面场强分布情况,同时给出了二维空间电荷限制流的一阶和二阶拟合公式。研究发现,真空二极管放电时阴极表面电场会随阴极注入电流密度的增加而增加,而后出现振荡并趋于一个稳定状态;二维空间电荷限制流密度值随阴极发射半径的增大而减小,且阴极发射半径越大越接近一维空间电荷限制流值。     

Analytical model of a corona discharge from a conical electrode under saturation

Exact partial solutions are found for the electric field distribution in the outer region of a stationary unipolar corona discharge from an ideal conical needle in the space-charge-limited current mode with allowance for the electric field dependence of the ion mobility. It is assumed that only the very tip of the cone is responsible for the discharge, i.e., that the ionization zone is a point. The solutions are obtained by joining the spherically symmetric potential distribution in the drift space and the self-similar potential distribution in the space-charge-free region. Such solutions are outside the framework of the conventional Deutsch approximation, according to which the space charge insignificantly influences the shape of equipotential surfaces and electric lines of force. The dependence is derived of the corona discharge saturation current on the apex angle of the conical electrode and applied potential difference. A simple analytical model is suggested that describes drift in the point-plane electrode geometry under saturation as a superposition of two exact solutions for the field potential. In terms of this model, the angular distribution of the current density over the massive plane electrode is derived, which agrees well with Warburg??s empirical law.     

基于库仑定律的二极管空间电荷限制效应研究

真空二极管是电子束源装置中的一个关键部件, 其阴极发射的电子束进入二极管阴阳极间隙区会产生很强的空间电荷限制效应. 本文针对平板真空二极管中的空间电荷限制效应物理模型, 从库仑定律的积分形式出发, 选取了不同参数的阴极半径与阴阳极间隙距离之比, 计算得到了真空二极管阴阳极间隙区的电场分布情况, 从而避免了采用Poisson方程求解时需要处理复杂的非线性偏微分方程这一问题. 结果表明, 基于库仑定律的计算结果与从Child-Langmuir定律分析得到的结果仅相差一个与二 极管极板边界条件有关的修正量. 当二极管阴极半径与阴阳极间隙距离之比 R/D>10时,一维空间电荷限制定律将是一个较好的近似结果,当 R/D较小时, 用该定律计算误差较大,在实际物理问题中需要谨慎使用.     

Electrode system of the high voltage glow discharge for metal heating

The electrode configuration of the high-voltage low pressure glow discharge with a cylindrical cathode for producing the annular beam of electrons is studied in this paper. Supposing that the space charge density is equal to zero the distribution of the electric field in the region between the electrodes is determined. The distribution of the electric field governs the processes in the discharge.The authors would like to express their thanks to Dr. J. Horsák for carrying out the numerical calculations.     

Negative space charge and electric field intensity in polymeric insulators at low temperatures

The effect of negative space charge accumulation due to injection of electrons from cathode microprotrusions on the steady-state and transient electric field distributions in polymer dielectrics is discussed. An isolated microprotrusion is modeled by a spherical capacitor in which an electrode of smaller radius is the cathode. The calculations include the fact that the distribution of negative space charge depends on the rate of capture and liberation of electrons by traps, while the activation energy of this process depends on the electric field intensity. An exponential energy distribution is proposed for the traps. It is shown that significant electrical overvoltages can only appear near the cathode microtips immediately after switching on the voltage. In the course of 10⁻⁶–10⁻⁵ s, the coefficient of electrical overvoltage drops to a few units and approaches its steady-state value. The region of significant electrical overvoltage is localized, and is the same order as the dimensions of the microtip. Fiz. Tverd. Tela (St. Petersburg) 40, 1167–1172 (June 1998)     

基于螺线管扫描法进行电磁叠加场中热发射度测量的仿真分析

在一种猝发高重频的X射线自由电子激光（XFEL）装置中,由于受到光阴极注入器内补偿螺线管与电子枪之间特殊结构的限制,阴极附近电场与磁场为叠加状态。实验中需要对阴极热发射度进行测量,而测量热发射度常用的螺线管扫描法基于几何发射度不变的前提,无法直接应用于电磁场叠加的结构。针对这一问题,考虑到归一化过程可以剔除电场对发射度的影响,基于此,研究归一化相空间中应用的螺线管扫描法,并通过仿真计算与分析,最终证明该方法适用于电磁叠加场中阴极热发射度的测量。     

Self-consistent structure of a dc discharge with a closed hall current in crossed electric and magnetic fields

A dc glow discharge with a closed Hall current in crossed electric and magnetic fields in helium is investigated. It is shown that the main features of an unmagnetized dc discharge [1] (such as the separation of the discharge into a space charge sheath and a quasineutral plasma, the formation of a cathode fall region and a negative glow, the appearance of a region with a reversed electric field producing a potential well for low-energy electrons and resulting in the formation of a Faraday dark space, and the formation of three pronounced groups of electrons in the electron distribution function) are also retained in a discharge in crossed fields. It is found that the sheath length is almost independent of the magnetic field, while the length of the negative glow region decreases appreciably with increasing magnetic field. The measured electron distribution function agrees well with the nonlocal theory, according to which the current in the Faraday dark space is carried by the intermediate electrons that are not trapped in the potential well and the energies of which are lower than the first excitation energy.     

分段表面放电沉积效率研究

利用一种结构紧凑的分段表面放电辐射源模块，详细研究了在不同电压、电容、气压实验条件下回路等效电阻、等效电感及放电能量沉积效率的变化规律，利用四分幅相机拍摄获得了不同实验条件下的放电等离子体通道图像，分析讨论了放电等离子体运动对放电能量沉积效率的影响，提出了提高能量放电沉积效率的有效途径。     

Effect of negative glow on the elementary processes occurring in the cathode region of a glow discharge

The role of the negative glow in producing charge carriers and the effect of this region on the elementary processes occurring in the region of cathode potential drop between plane parallel electrodes is considered in this paper.An estimate of the value of positive ion current passing to the cathode from the negative glow is made for nickel, copper, iron, and aluminum cathodes in hydrogen, and for an iron cathode in argon neon, and helium at 1 mm Hg pressure.Based on the values obtained for the ion current in the Crookes dark space, the electric field intensity and potential distributions are calculated and found to be in satisfactory agreement with the experimental data.     

Weakly relativistic and space charge effects in interaction of high-power microwave with plasma

In the present work, numerical studies on the effects of weakly relativistic ponderomotive force and space charge in the nonlinear interaction of a high-power microwave beam with a plasma are carried out. It is shown that, the profiles of the electron density and dielectric permittivity contain high peaks, and modulation of wavelength occurs in electron density distribution by increasing the microwave energy flux. In addition, it is indicated that the profiles of the electric and magnetic fields in relativistic regime are lengthened more than non-relativistic regime by increasing the initial electron density and the relativistic effects cause the increase in oscillation wavelength of electron density, dielectric permittivity and space charge field, in comparison with the non-relativistic regime. Finally, the results of the research show that the steepening in electron density distributions and their oscillation wavelength are enhanced, when the relativistic effects appear.     

Semi-analytical study of meniscus oscillation in an electrospray under AC voltage

In this paper, the oscillation of the meniscus in an electrospray with AC voltage is semi-analytically investigated. The electric field is achieved using the charge simulation method and the mutual interaction between the electric field and hydrodynamics is iteratively explored to investigate the oscillation. After determining the static meniscus shape on a nozzle, the meniscus oscillation is simulated under sinusoidal AC voltage. The semi-analytic simulation can offer the oscillating meniscus shapes and contours of the electric field outside the meniscus according to the applied frequency. Furthermore, the velocity profile of the liquid inside the meniscus is achieved.     

爆炸电子发射初期阴极表面电场的研究

为了研究二极管爆炸电子发射初始阶段阴极表面复杂的物理现象及规律, 建立了由场致电子发射阴极构成的一维平板真空二极管物理模型,通过自行编程数值求解泊松方程, 考虑了发射出的电子对阴极表面电场的非线性影响,自洽模拟得到了阴极表面电场随时间的变化情况. 模拟结果表明,爆炸电子发射初期,阴极表面电场随时间的增加而呈现出不断振荡的规律, 且振荡幅度越来越小,最终到达一个稳态的值,二极管两极板之间的外加电场越大, 阴极表面稳态电场的绝对值越大;电场增强系数越大,阴极表面稳态电场的绝对值越大. 在整个时间演变过程中,阴极表面的实际电场强度决定着阴极发射的电流密度大小, 反过来阴极发射的电流密度又会影响到阴极表面的电场.     

铁电介质阴极电子枪

 给出并分析了铁电介质阴极电子枪的初步数值模拟和实验结果。实验表明其发射电子密度可达110A/cm²。该种电子枪产生的电流密度大于阴极发射电子初始能量为零时的空间电荷限制电流,PIC数值模拟结果表明可以通过给发射电子赋予一定的初始能量来解释这一现象,理论分析认为铁电介质阴极发射电子具有初始能量是合理的。     

Attenuation of the Electric Potential and Field in Disordered Systems

We study the electric potential and field produced by disordered distributions of charge to see why clumps of charge do not produce large potentials or fields. The question is answered by evaluating the probability distribution of the electric potential and field in a totally disordered system that is overall electroneutral. An infinite system of point charges is called totally disordered if the locations of the points and the values of the charges are random. It is called electroneutral if the mean charge is zero. In one dimension, we show that the electric field is always small, of the order of the field of a single charge, and the spatial variations in potential are what can be produced by a single charge. In two and three dimensions, the electric field in similarly disordered electroneutral systems is usually small, with small variations. Interestingly, in two and three dimensional systems, the electric potential is usually very large, even though the electric field is not: large amounts of energy are needed to put together a typical disordered configuration of charges in two and three dimensions, but not in one dimension. If the system is locally electroneutral—as well as globally electroneutral—the potential is usually small in all dimensions. The properties considered here arise from the superposition of electric fields of quasi-static distributions of charge, as in non-metallic solids or ionic solutions. These properties are found in distributions of charge far from equilibrium.     

Anharmonic Bloch Oscillation of Electrons in Biased Superlattices

The oscillatory motion of electrons in a periodic potential under a constant applied electric field, known as Bloch oscillations (BO), is one of the most striking and intriguing quantum effects and was predicted more than eighty years ago. Oscillating electrons emit electromagnetic radiation and here we consider this BO effect for emission in the THz region. To date, it has been assumed that the Bloch oscillation of an electron is anharmonic oscillation, therefore with radiation emitted at the single Bloch frequency. We analyze scenarios when Bloch oscillations can be accompanied by the emission of radiation not only at the Bloch frequency but also with double and triple Bloch frequencies. The first scenario means that electrons could jump over neighboring Stark states. The second scenario of anharmonic emission is coupled to an opening of the minigap in the miniband.