Generation of Electron Beams in the Range of Forevacuum Pressures

This paper presents the results of a study on the generation of electron beams at gas pressures ranging from 0.01 to 0.1 Torr. The fact that this range of pressures is attainable with mechanical pumps only has provoked interest in this problem. To generate an electron beam, use is made of a plasma source based on a hollow-cathode discharge in combination with a plane-parallel acceleration gap. In the given range of pressures, the peculiarities of emission and acceleration of electrons are related to the high probability of ionization of the gas in the acceleration gap and to the formation of an ion flow propagating toward the electron beam. This causes a decrease in discharge operating voltage and also an increase in plasma density in the emission region. Two types of breakdown are observed in the acceleration gap: an interelectrode breakdown and a breakdown in the plasma–electrode system. The designed electron source allows one to obtain beams of cylindrical cross section with currents of up to 1 A and energies of up to 10 keV.     

用剪切干涉法测气动窗口流场对光束质量的影响

 利用横向剪切干涉仪对测量环境要求不高的优点,提出用横向剪切干涉仪测量气动窗口流场对光束质量的影响;给出测量原理,解决了干涉条纹难以判读的难点。并对稳定工作状态下自由旋涡气动窗口流场对光束质量的影响进行实验研究。以斯特列尔比为评价标准,测量给出自由旋涡气动窗口在稳定工作状态下对光束质量的影响程度。结果表明,当自由旋涡气动窗口工作在理论设计条件下时,对光束质量的影响比较小,能较好满足任务需要。     

Chordwise spacing aerodynamic detuning for unstalled supersonic flutter stability enhancement

Unstalled supersonic flutter is a significant problem in the development of advanced gas turbines because it restricts the high speed operating range of the engine. A new approach to passive control of unstalled supersonic flutter is aerodynamic detuning, defined as designed passage-to-passage differences in the unsteady aerodynamics of a blade row. In this paper, a mathematical model is developed to predict the unstalled torsion mode stability of an aerodynamically detuned turbomachine rotor operating in a supersonic inlet flow field with a subsonic axial component, with the aerodynamic detuning accomplished by alternate chordwise spacing of adjacent rotor blades. The unsteady aerodynamic moments acting on the blading are calculated in terms of influence coefficients. The stability enhancement associated with this alternate chordwise aerodynamic detuning is demonstrated utilizing an unstable twelve bladed rotor based on Verdon's Cascade B flow geometry. This model and unstable baseline rotor configuration are then used to show that axial spacing detuning leads to greater flutter stability enhancement than does circumferential spacing aerodynamic detuning. Finally, the trade-offs between structural damping, alternate chordwise aerodynamic detuning, and alternate circumferential aerodynamic detuning are considered.     

Dynamics of the Formation of a Virtual Cathode in an Electron Beam Passing through a Dielectric

An analytical solution of the problem on the initial stage of the formation of a virtual cathode in an electron beam passing through a dielectric medium is presented.     

Passage of a high-current relativistic electron beam through matter

A solution is presented for the problem of passage of a high-current relativistic electron beam through matter in the stationary case with one-dimensional geometry. The system of equations describing the passage of the beam consists of the kinetic equation for fast electrons, which considers the effect of the electric field on the magnitude and direction of particle momentum, the equations for the field produced by the space charge generated by thermalized electrons, and relations connecting the conductivity of the medium to the radiation field. Higher-order perturbation theory is used for the solution. The solutions reveal that the distribution of expended energy, thermalized electrons, and other properties of the flow are highly dependent on the density of the incident flux and the conductivity of the medium. It will be shown that linear transfer theory may be applied to calculation of the passage of high-current beams through matter over a wide range of currents and conductivities, if the barrier thickness does not exceed one-half the path length, but cannot be used for calculation of passage through large-thickness barriers, i.e., with thickness comparable to the electron free path length.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 67–74, September, 1979.The author thanks A. N. Didenko and A. M. Kol'chuzhkin for their evaluation of the study.     

Kinetic equation for a relativistic electron beam propagating along an external magnetic field in dense and rare gas-plasma media

A kinetic equation that describes the transverse dynamics of an axisymmetric paraxial relativistic electron beam propagating along an external magnetic field in a gas-plasma medium is derived with allowance for the influence of the self-consistent electromagnetic field on the beam, the effects related to the nonlaminar motion and rotation of the beam electrons at the exit from the injector, and the scattering and energy loss of the beam electrons in their collisions with the neutral particles of the background gas.     

1THz回旋管双阳极磁控注入电子枪的分析及设计

基于电子光学理论,通过编程进行大量的数值计算,设计了一支用于1THz回旋管的双阳极磁控注入式电子枪.对双阳极磁控注入电子枪的计算及设计进行了阐述,并对1 THz回旋管电子枪中高磁压缩比(f_m=125)可能导致电子反转的问题进行了详细的分析和模拟.通过对电子枪进行了仿真和优化,最后计算和设计了一支速度比适中(α=1.3),速度零散较小(Δβ<8%) 的电子枪.     

System for transporting an electron beam to the atmosphere for a gun with a plasma emitter

We report on the results of simulation of the gas flow in a gun with a plasma emitter and in the system for extracting the electron beam to the atmosphere, constructed on the basis of standard gasdynamic windows (GDWs). The design of the gun and GDWs is described. Calculations are performed for a pressure of about 10^–3 Torr in the electron beam generation range. It is shown that the pressure drop to the atmospheric pressure in the system of electron beam extraction to the atmosphere can be ensured by two GDW stages evacuated by pumps with optimal performance.     

Beam-plasma discharge in the propagation of a long-pulse relativistic electron beam in a medium-pressure rarefied gas

A theoretical model is given, along with a numerical analysis of the evolution of beam-plasma discharge in the propagation of a long-pulse relativistic electron beam in a rarefied gas at medium pressure. It is shown that the self-stabilization of beam-plasma discharge as a result of longitudinal inhomogeneity of the density of the discharge plasma makes it possible for the beam to traverse the beam chamber with relatively low total energy losses, including ionization losses and energy losses in the generation of oscillations. During the dissociative recombination of electrons and ions of the discharge-driven plasma, heat is released and spent in raising the temperature of the gas. The investigated collective-discharge mechanism underlying heating of the gas for a relativistic beam can be more efficient than the classical heating mechanism due to ionization losses of the beam in pair collisions of its electrons with gas particles. Zh. Tekh. Fiz. 67, 94–98 (May 1997)     

Anode plasma structure in a gas discharge with neutral density depleted by ionization

We consider the anode plasma structure in a gas discharge with density of neutral atoms (neutrals) depleted by strong ionization. We obtain analytical solutions of the quasi-neutrality equation for the potential distribution and a condition for the existence of anode plasma in the one-dimensional case for arbitrary potential dependences of the neutral depletion frequency and the electron density. We consider the special cases of a constant neutral depletion frequency, ionization by Maxwellian electrons, and ionization by an intense electron beam under the conditions of collisionless ion motion and Boltzmann thermal electron distribution. The solutions for the first two cases at zero depletion parameter, i.e., at constant gas density, match those obtained in [1] by a power series expansion. In the case of ionization by Maxwellian electrons, the formation of anode plasma at reasonable working-gas flow rates is shown to be possible only at a fairly high electron temperature (if, e.g., xenon is used as the working gas, then T _e ≥ 5 eV). Steady-state solutions of the quasi-neutrality equation under ionization by an intense electron beam exist only if the ratio of the electron beam density to the maximum thermal electron density does not exceed a certain limiting value.     

Formation of plasma dust structures at atmospheric pressure

The formation of strongly coupled stable dust structures in the plasma produced by an electron beam at atmospheric pressure was detected experimentally. Analytical expressions were derived for the ionization rate of a gas by an electron beam in an axially symmetric geometry by comparing experimental data with Monte Carlo calculations. Self-consistent one-dimensional simulations of the beam plasma were performed in the diffusion drift approximation of charged plasma particle transport with electron diffusion to determine the dust particle levitation conditions. Since almost all of the applied voltage drops on the cathode layer in the Thomson glow regime of a non-self-sustained gas discharge, a distribution of the electric field that grows toward the cathode is produced in it; this field together with the gravity produces a potential well in which the dust particles levitate to form a stable disk-shaped structure. The nonideality parameters of the dust component in the formation region of a highly ordered quasi-crystalline structure calculated using computational data for the dust particle charging problem were found to be higher than the critical value after exceeding which an ensemble of particles with a Yukawa interaction should pass to the crystalline state.     

Long pulse ultraviolet laser emissions in an aerodynamically cooled electron-beam excited Ne-NF3 mixture

Long pulse laser action has been achieved at 3378.28 and 3481.96 Å in an electron beam excited supersonic flow. These laser emissions, attributed to NeII transitions, have been obtained when a mixture of Ne and NF₃ at a pressure of 0.2 atm. and aerodynamically cooled to 80 K was excited by a medium intensity electron beam. Laser pulse duration, about 350 ns fwhm for both lines, was only limited by the electron beam pulse length. The second of these laser lines had not been previously reported.     

Hose instability and wake generation by an intense electron beam in a self-ionized gas

The propagation of an intense relativistic electron beam through a gas that is self-ionized by the beam's space charge and wakefields is examined analytically and with 3D particle-in-cell simulations. Instability arises from the coupling between a beam and the offset plasma channel it creates when it is perturbed. The traditional electron hose instability in a preformed plasma is replaced with this slower growth instability depending on the radius of the ionization channel compared to the electron blowout radius. A new regime for hose stable plasma wakefield acceleration is suggested.     

Passage of a Gaussian Beam through a Gradient Medium

The problem of the passage of a Gaussian laser beam of light through a layer of gradient medium, whose dielectric permeability changes linearly in a direction approximately perpendicular to that of the propagation of the beam, is solved in the paraxial–optics approximation. The center of the beam in this medium propagates along a parabola, its divergence is independent of the parameter of the medium inhomogeneity, while the phase front remains approximately spherical.     

大面积均匀电子束产生实验研究

 在电子束泵浦气体激光实验中,大面积均匀电子束是获得高效能激光输出的必要条件。介绍了利用SPG-200脉冲功率源产生大面积均匀电子束的实验。SPG-200是基于SOS的全固态重复频率脉冲功率源,其开路电压大于350 kV。用于产生电子束的真空二极管阴极长294 mm,宽24 mm,两端均为半径为12 mm的半圆,栅网平面为阳极面,两者之间的距离在0~49 mm可调,阴极发射的电子束通过用于隔离激光气室和二极管真空室的压力膜及其支撑栅网引出。分别以石墨和天鹅绒为阴极材料,获得了大面积电子束输出,给出了二极管参数的测量结果,并对电子束发射均匀性进行了诊断。实验结果表明：在阴极材料为石墨、阴阳极间隙为5~9 mm时,二极管电压为240~280 kV,二极管电流为0.7~1.8 kA,输出的电子束很不均匀;在阴极材料为天鹅绒、阴阳极间隙为31~46 mm时,二极管电压为200~250 kV,二极管电流为1.5~1.7 kA,输出的电子束均匀性较好。     

电子束与烟气相互作用机制模拟分析

 电子束在烟气中穿透深度和剂量分布将直接影响废气中硫、氮氧化物的脱除效率。通过理论计算和蒙特卡罗模拟计算得到不同能量电子穿过各种厚度加速器箔窗后能量损失情况；对不同入射能量电子束在烟气中透射深度和轨迹分布进行了模拟计算。结果表明：电子束反应最佳能量为700 keV；利用产生1 m长线状束流的电子加速器进行双面照射，烟道反应室横截面最佳尺寸为1.0 m×3.5 m。     

基于气动反问题的风力机翼型优化设计

翼型气动优化设计的核心在于快速、准确的流动性能分析与快速、可靠的寻优算法。本文提出通过控制翼型表面预期流动分布,应用气动反问题方法,求解性能优化的翼型气动设计新方法。本文的翼型流动分析是基于位势流动与边界层积分方程的迭代解法。气动参数寻优采用了基于多变量搜索的加速POWELL算法,在确定的参数空间内,遍历搜索最佳性能点,可以保证最终优化解的全局性。气动反问题求解采用了壁面喷吸气模型。计算案例表明,本文方法的计算时间少,在流动不分离时具有与RANS同等计算精度,为快速开发低速风力机翼型提供了一个有效的设计方法。     

Dissipative instability of a highly relativistic electron beam through the excitation of surface waves on a conducting medium

The possibility of the dissipative instability of a relativistic electron beam streaming near a conducting medium is investigated. The development of this dissipative beam instability through the surface wave excitation slightly disturbs the beam leading to the slightly heating of the conducting medium.     

A COUPLED FLUID-STRUCTURE ANALYSIS FOR 3-D INVISCID FLUTTER OF IV STANDARD CONFIGURATION

A three-dimensional non-linear time-marching method and numerical analysis for aeroelastic behaviour of an oscillating blade row is presented. The approach is based on the solution of the coupled fluid-structure problem in which the aerodynamic and structural equations are integrated simultaneously in time. In this formulation of a coupled problem, the interblade phase angle at which a stability (or instability) would occur is a part of the solution. The ideal gas flow through multiple interblade passage (with periodicity on the whole annulus) is described by the unsteady Euler equations in the form of conservative laws, which are integrated by use of the explicit monotonic second order accurate Godunov-Kolgan volume scheme and a moving hybrid H-H (or H-O) grid. The structure analysis uses the modal approach and 3-D finite element model of the blade. The blade motion is assumed to be a linear combination of modes shapes with the modal coefficients depending on time. The influence of the natural frequencies on the aerodynamic coefficient and aeroelastic coupled oscillations for the Fourth Standard Configuration is shown. The stability (instability) areas for the modes are obtained. It has been shown that interaction between modes plays an important role in the aeroelastic blade response. This interaction has an essentially non-linear character and leads to blade limit cycle oscillations.     

进气量对强流正离子源反向电子流的影响研究

分析了EAST-NBI离子源束引出过程中反向电子的产生及物理特性,对典型情况下的进气量对离子源的影响进行了计算和实验研究.实验结果发现,质子比受进气量影响较小,进气量与反向电子流呈明显正相关.