Feasibility Study of Axially- Extracted Virtual Cathode Oscillator

In this paper, we have analyzed the design parameters of the axially - extracted virtual cathode oscillator, which is high-power microwave source based on the concept of the virtual cathode associated with the intense relativistic electrons beam oscillations in the electrostatic potential well. The microwave emission by the virtual cathode oscillator results from both the space and time oscillations of virtual cathode and reflexing electrons trapped in the potential well between the virtual and real cathodes. In the X-band frequency spectrum 700 MW microwave peak power has been obtained analytically by the solid electron beam of 300 kV and 20 kA for feasible design parameters. The analysis has been performed by 2-dimensional, relativistic, electromagnetic particle-in-cell simulation code XOOPIC.     

Beam buildup in a DEMATRON amplifier

The operation of an RF triggered cold-cathode crossed-field amplifier is briefly described, and the problem is posed of how the beam builds up, since it is necessary for it to remain in an inherently debunching phase region for more than 20 successive impacts on the cathode. A partial answer is provided by numerical calculations showing that the velocity of a repeatedly impacting beam differs from E/B in a way which introduces a new phase-focusing mechanism. It is found that buildup can also occur without exact synchronism over a range of calculated voltages which agree closely with measurement. The principles of two computer programs are described, one covering the buildup region of negligible space charge, and the other the transition and power-generating regions where space charge becomes important. Quantitative conclusions are drawn concerning the velocity and direction of impacts on the cathode, which vary markedly as the space charge density changes.     

HB2电子枪中空间电荷效应的研究

以阴极射线管(CRT)为例,研究了在不同发射电流下空间电荷效应对荧光屏上电子束点大小的影响。研究结果显示,当阴极电流大于1mA时,空间电荷效应开始起显著作用,而当阴极电流小于1mA时,空间电荷效应的影响逐渐减小,以致可以不考虑。此外,除了空间电荷效应最严重的阴极区外,主透镜区和漂移区的空间电荷效应相对预聚焦区较为显著。     

Chaotic oscillations in electron beam with virtual cathode in external magnetic field

This article presents the results of a numerical study of external magnetic field influence on the conditions and mechanisms of virtual cathode (VC) formation in a relativistic electron beam. It also considers other related issues, e.g. peculiarities of nonlinear dynamics of electron beam with VC under changed external magnetic field, different mechanisms of VC oscillation chaotisation leading to complication of vircator system dynamics and appearance of multi-frequency VC oscillations. General systemic mechanism of VC oscillation chaotisation has been identified which is connected with formation of electronic patterns in electron beam whose interaction in the common field of spatial charge determines appearance of additional inner feedback. Transition from chaotic to periodical oscillation regime is found to be connected with destroying the mechanism of secondary electronic structures (electron bunches) formation. Besides, the influence of extent of screening of electron gun from magnetic field is discussed.     

Experimental Analysis of Pseudospark Sourced Electron Beam

The pseudospark (PS) discharge has been shown to be a promising source of high brightness, high intensity electron beam pulses. The PS discharge sourced electron beam has potential applications in plasma filled microwave sources where normal material cathode cannot be used. Analysis of the electron beam profile has been done experimentally for different applied voltages. The investigation has been carried out at different axial and radial location inside the drift space in argon atmosphere. This paper represents experimentally found axial and radial variation of the beam current inside the drift tube of PS discharge based plasma cathode electron (PCE) gun. With the help of current density estimation the focusing and defocusing point of electron beam in axial direction can be analyzed.     

Equilibrium solutions for partially immersed relativistic electron beams

The equations relating the beam radius and axial electron velocity to easily measurable external beam parameters are developed for solid, relativistic beams. The beam parameters are tunnel voltage, beam current, axial magnetic field, cathode magnetic field, tunnel radius, and cathode radius. The equations are sufficiently complex to warrant the use of a digital computer if many cases are to be evaluated. Error indicators are formulated to prevent use of the relations beyond their range of validity. The equilibrium solutions for relativistic electron beams from unshielded cathodes show that the required magnetic focusing field is lower than that computed from nonrelativistic formulas. The angular magnetic field produced by the beam itself aids in focusing the electrons. The potential depression due to space charge is analyzed. Correction curves are given which allow the use of nonrelativistic equations in predicting equilibrium behavior. The maximum possible microperveance of relativistic beams is shown to be lower than the classical value of 25.4.     

均匀磁聚焦和周期磁聚焦部分屏蔽流过渡区的设计

本文叙述均匀磁聚焦和周期磁聚焦部分屏蔽流过渡区设计的一种方法,指出对于阳极电位与慢波线电位不同的电子光学系统,以及这两个电位虽然相同,但导流系数大,阳极孔效应严重的电子光学系统,它们的过渡区的设计,必须采用非等位空间中的傍轴电子轨迹方程。并对用部分屏蔽流周期磁聚焦的电子光学系统,电子枪区中的电子轨迹与磁力线重合的问题提出一些看法。     

Radial and Axial Electron Concentrations in an Oscillating Low Voltage Arc†

Measurements have been made of the plasma electron concentration (n) along and perpendicular to the axis of a low pressure, low voltage oscillating discharge with cylindrical symmetry, maintained by an axially directed beam from a small cathode. The contours of n are sharply peaked radially at the axis between the cathode and oscillation front (meniscus), but are much flatter beyond the meniscus, near the anode. The radial contours between cathode and meniscus conform approximately to those predicted theoretically for axial electron generation, and those near the anode to those predicted theoretically for ion generation proportional to electron concentration. Contours near the meniscus, when not completely unobtainable on account of the oscillations, exhibit apparent radial maxima and minima associated with the beam diverging from the meniscus.     

Relaxation instabilities in high-perveance electron beams

Spurious low-frequency oscillations similar to those reported by Cutler have been observed in the form of large amplitude modulation of both the RF output and the collector current of klystrons utilizing high-perveance electron beams. This modulation, which appears typically as sawtooth-like relaxation oscillations with frequencies ranging from 10 cps to 100 kc, was observed to occur spontaneously only if the operating pressure was lower than a critical threshold (approx 1 times 10^{-7}mm Hg). Experiments are described which were designed to investigate this phenomenon using dc beam testers. Evidence is presented which indicates that the oscillations are due to a relaxation back and forth between two possible solutions to Poisson's equation which both satisfy all boundary conditions. One of the possible solutions corresponds to the existence of a virtual cathode within the beam, resulting in a partial reflection of electrons. Experimental evidence indicates that positive ions play an important role in triggering the relaxation. Both theoretical and experimental evidence are presented which point to relaxation instabilities of the type described as a potential hazard in utilizing depressed collector operation for improved efficiency of high-perveance microwave tubes. The same potential hazard exists in the use of periodic electrostatic focusing.     

测量热阴极次级电子发射的新方法及其应用

本文利用相关检测技术,并对测试管结构作了改进,很好地抑制了热电子本底及空间电荷效应,构成一种测量热阴极在工作温度下次级电子发射性能的新方法。以浸渍钪酸盐阴极为样品,测得在低的轰击电子能量和电子流情况下次级电子发射系数占随温度指数上升;轰击电子能量或轰击电子流较大时,温度对没有很大的影响。研究表明高温下钪酸盐阴极存在电子轰击热发射增大效应,对此本文提出内建场模型加以解释。     

平面平行真空微电子二极管中二分之三次方关系式的应用

在一定的假定条件下，考虑空间电荷影响，平面平行真空微电子（P—VMD）二极管中电流一电压近似按二分之三次方关系式工作。本文在此关系式及Forler—Nordheim场发射方程的基础上，通过解简化立方方程，进一步推导出管内的电位、电场强度、电子速度和空间电荷密度的分布函数。P-VMD二极管在保持管内结构与阴极表面电场强度不变，并工作在典型工作状态（归一化电位系数P=2／3）情况下，考虑空间电荷影响时的阳极电压、阳极电场强度和阳极电子速度分别比无空间电荷影响时增加约50．00％，73．21％和22．47％。P—VMD二极管内的空间电荷密度分布函数为正割函数，在阳极表面附近为最小，在阴极表面处为无穷大，这是由于本文假设在阴极表面处的电子初速度为零的缘故。     

多能谱电子束能量分布的蒙特卡罗模拟和空间电荷效应

利用电子束穿越固体薄膜时,束电子与固体中的原子或电子之间的相互作用而产生能量改变,是获取多能谱电子束的一种方便可行的理想途径。通过改变薄膜材料或组份、薄膜厚度以及入射电子束的能量和方向等,可以得到各种不同能量分布的电子束。为了预测多能束的能量分布,我们采用蒙特卡罗模拟计算电子在固体中的散射效应。得到的透射系数和透射电子的能谱与实验测量结果一致。为计算多种能量电子共存空间的电位分布,我们对多能电子束在均匀电场或无场空间中的空间电荷效应进行了分析计算。     

Two dimensional plotting of semiconductor resistivity by scanning electron microscope

A method for the measurement of the resistivity of semiconductor samples is described which uses the electron beam of a scanning electron microscope as probe. This technique provides high local resolution (about 10 μm), causes no damage of the semiconductor material and is fast so that the two dimensional distribution of the resistivity can be plotted on a cathode ray tube. The sample, however, must be prepared to have a large area blocking Schottky-contact. The focussed electron beam generates carriers in a space charge region below a thin metal contact. The measurement is based on the change of the I-V characteristic of the Schottky diode caused by the spreading resistance from the point of the carrier generation to the bulk. Experimental results are presented as well as a theoretical evaluation of the sensitivity of this measuring technique.     

Space charge characteristics of an insulating thin film negatively charged by a low-energy electron beam

In this study, based on a comprehensive numerical simulation of self-consistent charging, we investigate the formation, evolution and influencing factors of space charge distributions for a grounded insulating thin film of SiO(2) negatively charged by a keV non-penetrating focused electron beam. The simulated space charge presents first positive distributions and then negative ones along both the radial and depth directions because of the difference between electron and hole transports. The variations in distribution occur within a range of the minimum potential acting as a potential barrier for carrier transport. The negative space charge is distributed more widely and deeply, though its peak value in density is usually lower than that of the positive one. Electrons trapped outside the minimum potential range dominate the strength of negative charging. With the increase in potential barrier and the occurrence of leakage current, the space charge eventually reaches equilibrium and exhibits an approximately one-dimensional axial distribution outside the minimum potential range. Distribution features of the space charge density in the equilibrium state correlate with the film and beam parameters via transients of the leakage current. These results and analyses provide new insights into the negative charging effects involved in various electron-beam-based surface microscopic methods, analyses and fabrication techniques.     

静电电子回旋脉塞的理论分析

本文考虑了电子注厚度及交、直流空间电荷效应以后,对静电电子回旋谐振脉塞(EECRM)进行了理论分析,并讨论了其特性的变化情况。     

Avalanche-initiated space-charge oscillations

Physical mechanisms are proposed for avalanche oscillations in n⁺-n-n⁺semiconductor structures. A linearized analysis is proposed for these mechanisms, the results of which agree well with the results of a large-signal computer simulation. The oscillation mechanism is dependent upon a large excess electron concentration that is present at high current levels in the n region of an n⁺-n-n⁺structure. This electron concentration causes a net negative space charge in the n region, which in turn causes the electric field to be nonuniform, peaking at the anode n⁺contact. At sufficiently high current densities, an avalanche zone will form at the anode contact. The resultant carrier generation in this zone creates a hole domain of density sufficient to quench the avalanche. This hole domain then travels across the n region under the influence of the field. The positive space charge of the hole domain depresses the field sufficiently to prevent avalanche from recurring at the anode until the domain has extracted at the cathode. The field variation during this cycle causes transit-time terminal voltage oscillations. It is shown how, under proper conditions, a steady-state plasma region may be established over a substantial portion of the device length. This plasma region will cause the device to exhibit a negative differential resistance, and will also support relaxation oscillations at a frequency comparable to the reciprocal of its extraction time.     

Development of the 75-GHz planar gyrotron with transverse energy extraction

The opportunity of generating ribbon-shaped polyhelical electron beams intended to excite oscillations in the new type of gyrotrons is investigated via particle-in-cell simulation. Its distinctive features are the planar geometry of an interaction space and transverse energy extraction (with respect to the direction of translational motion of a helical electron beam). The electrode configuration has been found in the gyrotron with an operating frequency 75 GHz, where the formed electron beam has a velocity spread of ～10%, the rotational energy fraction is 50%, and the beam profile is weakly distorted. When the voltage is 12 kV and the beam current is 1 A, the electron beam under study is demonstrated to excite the single-mode generation with an efficiency of up to 15% in the gyrotron’s operating space produced by the planar waveguide.     

有强相对论性非中和电子束环的环形自由电子激光器理论

本文用弗拉索夫-麦克斯韦方程研究了有强相对论性非中和电子束环的环形自由电子激光器的工作特性。结果表明,强电子束的空间电荷效应有提高辐射频率和强度的作用。     

New Type of the Electron Emission Induced by the Electric Field

A new type of the electron emission induced by a pulsed electric field with a strength of about 105 V/cm applied to the cathode made of graphene-like structures has been found. Pulsed currents of up to several hundred amperes have been obtained in a range of 1–5 ns. It has been found that the length of the current pulse depends on the strength of the electric field and decreases with an increase in this strength at a constant length of the electric field pulse; the electron emission time as well as the maximum emission current are determined by the value of the bound charge in the region of the cathode surface; and the process relaxation time after extraction of the emission current exceeds 300 ns.     

速调管双间隙输出段的效率计算

本文在计算速调管双间隙输出段的效率时,不沿用传统的花费时间的电子圆盘时间积分法和过于简单化的空间电荷波法,而提出了一种新的综合性的计算方法。使用这种方法其所需计算时间比电子圆盘法要少得多;计算结果与热测结果基本吻合。