Injection of Intense Relativistic Electron Beams into a Toroidal Geometry

Two experimentally verified methods are presented for the injection of high-current relativistic electron beams (30 kA, 400 kV) into strong toroidal magnetic fields (1-8 kGauss). Injection is accomplished by contouring the current flow in the stalk of a field-emission cathode to perturb the flux lines only during beam generation. On conclusion of the emission process the perturbed lines can return to their original positions thereby trapping the beam.     

Formation and Diagnostics of Intense Relativistic Helical Electron Beams for Gyrotrons

We develop a magnetron-injection gun for a 1-cm wavelength gyrotron, which allows us to increase the operating current up to 50% of the Langmuir current of the gun by reducing the time required to bring electrons to the high-potential region. To measure the velocity distributions in helical electron beams for energies of several hundreds of keV, we propose, develop, and study a new electron-velocity distribution analyzer based on the phenomenon of electron reflection from an adiabatic magnetic mirror. The results of our study demonstrate that the gun is capable of forming high-quality intense beams suitable for generating microsecond microwave radiation with power higher than 10 MW in gyrotrons.     

Experimental Studies of Intense Pulsed Large-Area Electron Beams

We develop methods for studying intense long-pulsed large-area electron beams. Spatial and energy parameters of electron beams at the GESA technological facility are determined. Space-charge oscillations in such beams are discovered and possible explanations of the nature of these oscillations and their influence on the electron energy spectrum are proposed.     

Diode Feedback Effects in Intense Relativistic Electron Beam Oscillators

The general operation of intense relativistic electron beam oscillators is described. These oscillators employ the well-known reflex triode phenomenon to plug the ends of a magnetically confined beam drift region by setting up efficient electron reflexing between the real cathode of an accelerator and a downstream virtual cathode. For a variety of magnetic traps and experimental conditions, it is shown that the inherent electron beam feedback from the drift region can be effectively utilized to reduce the electronion diode impedance and thereby permit good matching and energy transfer between the diode and a sub-ohm particle accelerator. A theoretical model is presented to interpret the observed phenomena.     

四光束对高能电子的捕获特性研究

依据非线性强场效应的基本原理,提出了一种四光束捕获电子的方案,旨在通过延长电子和强场相互作用时间来提高非线性过程发生的总概率,实现观测信号的增强。其基本原理是基于电子在强激光光束上的非弹性散射。数值模拟结果表明,捕获后的电子和中心光场的相互作用时间得到延长。     

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.     

X-Ray Bremsstrahlung Measurements of an Intense Relativistic Electron Beam Propagating in a Plasma

Information on the peak electron energy, angular spread, and current density of a relativistic electron beam propagating in a plasma column is obtained from measurements of two-absorber transmission ratios, anistropy, and intensity, respectively, of x-ray bremsstrahlung from thin target foils in the plasma. Measurements indicate a 10% loss in peak electron energy and a factor of two loss in peak beam intensity over the distance of the plasma column, and show a large angular spread in the beam.     

Surface Wave Generation in a Solid State Plasma by Relativistic Electron Beams

The linear and nonlinear theory of the surface wave generation in solid-state plasma by a relativistic electron beam propagating in a gaseous plasma is treated. The proposed scheme is in better agreement with the conditions of real experiment. Besides, the neutralization of beam charge is possible and the oscillation frequency and its stability increase, etc. A nonlinear analysis permits to obtain the estimation of efficiency of the beam interaction with the surface wave and a number of other characteristics of the system.     

喷气式Z箍缩等离子体装置中离子束能谱的测量

利用新研制的紧凑型汤姆生离子能谱仪（ＴｈｏｍｓｏｎＩｏｎＥｎｅｒｇｙＡｎａｌｙｚｅｒ），对喷气式Ｚ－箍缩等离子体装置中离子能谱进行了测量，在ＣＲ－３９上得到了清晰的Ａｒ＋，Ａｒ２＋，Ａｒ３＋离子抛物线轨迹，通过分析计算结果表明：离子的最大能量在１ＭｅＶ左右，离子能谱分布曲线都随其能量增加而单调下降。     

Study of Intense Electron Beams Produced by High-Voltage Pulsed Glow Discharges

We report the generation of high-current-density (20 A/cm2) pulsed electron beams from high-voltage (48-100 kV) glow discharges using cathodes 7.5 cm in diameter. The pulse duration was determined by the energy of the pulse generator and varied between 0.2 ?s and several microseconds, depending on the discharge current. The largest electron beam current (900 A) was obtained with an oxidized aluminum cathode in a helium-oxygen atmosphere. An oxidized magnesium cathode produced similar results, and a molybdenum cathode operated at considerably lower currents. A small-diameter (<1 mm) well-collimated beam of energetic electrons of very high current density (>1 kA/cm2) was also observed to develop in the center of the discharge. Electrostatic probe measurements show that the negative glow plasma density and the electron beam current have a similar spatial distribution. Electron temperatures of 1-1.5 eV were measured at 7 cm from the cathode. The plasma density (8.5 · 1011 cm-3 at 450 A) was found to depend linearly on the discharge current. In discharges at high currents a denser and higher temperature plasma region was observed to develop at approximately 20 cm from the cathode. We have modeled the process of electron beam generation and predicted the energy distribution of the electron beam. More than 95 percent of the electron beam energy is calculated to be within 10 percent of that corresponding to the discharge voltage.     

Z“箍缩”的时间分辨测量技术研究

针对在阳加速器上进行的Z箍缩内爆实验所要求的超快分幅摄影技术研究,主要利用八个微通道板构成摄影系统的快门以达到时间分辨的要求,同时解决了在阳加速器上的精密同步问题以使系统可以稳定、可靠地一次拍摄到八幅图像,图像间隔最小为10 ns,曝光时间可达到3 ns.该技术以分幅原理获得大幅面的图像数据,具有图像特征清晰、空间信息详细的特点,为Z箍缩过程的研究提供了翔实的实验数据.     

Theory of a Two-Gas Gas-Puff Z Pinch

A simple snow-plow model for the two-gas gas-puff Z pinch is investigated. An expression for the plasma velocity in the central test-gas region is derived and the radius of maximum compression determined.     

Numerical Simulation Models of Forming Systems of Intense Gyrotron Helical Electron Beams

Potentialities of different numerical models for calculation of helical electron beams parameters are analyzed. The most simple and economical with respect to the calculation time static mono-velocity model, as well as the model considering initial velocities of electrons and the dynamic model based on the PIC-method and on the quasi-static concept of the electric field are described. The main physical results obtained on the basis if each model mentioned above are given.     

Linear Theory of Radially Inhomogeneous, Unneutralized, Relativistic Electron Beams

A set of four, coupled, first-order differential equations describing the normal modes of a cylindrically symmetric, cold fluid, unneutralized, relativistic electron beam of arbitrary radial profile is derived. Effects of beam rotation and equilibrium fields are treated exactly. The differential equations are found to have singular points for a radially inhomogeneous beam wherever the eigenfrequency equals the cyclotron or Doppler resonance frequencies. The resulting branch cuts in the dispersion function give rise to secularly decaying contributions to the initial value problem. The rate of decay and the character of the eigenmode near the singularity are determined from the solution of the corresponding indicial equation. Discrete eigenmodes also exist and are obtained by numerical solution of the differential equations and boundary conditions. For realistic solid-beam equilibria, only one slow cyclotron-mode exists for any given pair of axial and azimuthal wavenumbers, and that mode is localized at the beam edge. Under identical conditions several slow space-charge modes exist and are not so distorted. However, even at the space-charge limit, the phase velocity of long-wavelength slow space-charge waves does not decrease to zero. These results are relevant to the Autoresonant and Converging Guide collective ion acceleration proposals.     

Theory of Microwave Emission by Velocity-Space Instabilities of an Intense Relativistic Electron Beam

The stability of waveguide modes in a waveguide along which is propagated an unneutralized, intense beam of relativistic electrons guided by an applied axial magnetic field is considered. It is found that the waveguide mode can interact unstably with the beam by resonating with the Doppler shifted cyclotron frequency of the beam. This instability appears to be the mechanism by which microwaves are produced in some recent experiments which are discussed.     

纳秒强流脉冲电子束强化金属表面的研究

利用多极板赝火花放电装置产生的高功率脉冲电子束对不同类型的钢, 如45#, 65Mn, T8, 9Cr18和GCr15等进行轰击, 研究其在金属材料表面改性中的应用. 样品表面的显微硬度和耐腐蚀性测试结果以及扫描电子显微镜(SEM)的观察分析表明, 经电子束轰击后, 这些材料在结构、组织和性能上发生了明显的变化, 轰击中心区域的显微硬度和耐蚀性明显提高. 基于一维热传导方程对材料表面的冷却速率进行了估算, 对电子束与金属材料的作用过程进行了理论分析. 结果表明, 高功率密度脉冲电子束与金属材料相互作用, 表面冷却速率高达1. 2×1012 ℃/s, 使材料表面局部瞬间达到熔化, 产生骤热急冷过程. High power density electron beams generated by multiplate pseudospark discharge chamber, have been used to bombard various kinds of steel targets such as 45#, 65Mn, T8, 9Cr18, GCr15, etc, and studyits applications for modification of metal surface. The microhardness and corrosive resistance property have been measured and the morphology was obtained by using SEM analysis. The results showed that the surface properties and structure of the matevials bom barded have been modified; in the bombarded center area, the microhardness as well as corrosive resistance property was improved obviously. The interactions befween the electron beam and metal materials were theoretically considered and discussed on the basis of simple calculation with one dimensional thermal transfer equation. It showed that the cooling rate of metal surface with 1.2×1012 ℃/s was so high that caused the metal surface instant melted, and abrupt cooled.     

天鹅绒阴极产生的双脉冲强流相对论电子束特性实验研究

在时间分辨的模式下, 实验研究了天鹅绒阴极产生的双脉冲相对论强流电子束的束心运动、束包络和束的发射度. 在实验中, 电子束流强度和电子束心运动用电阻环进行测试, 而电子束和石英玻璃的相互作用产生的契仑科夫辐射用来给出电子束包络和发射度信息. 电子束和石英玻璃作用产生的契仑科夫辐射用1台8幅分幅相机记录. 实验结果表明, 天鹅绒阴极产生的相对论强流双脉冲电子束在束流大小、束心运动轨迹、束包络及束发射度等方面具有较好的一致性.     

Self-Injection and Acceleration of Monoenergetic Electron Beams from Laser Wakefield Accelerators in a Highly Relativistic Regime

Self-injection and acceleration of monoenergetic electron beams from laser wakefield accelerators are first investigated in the highly relativistic regime, using 100 TW class, 27 fs laser pulses. Quasi-monoenergetic multi- bunched beams with energies as high as multi-hundredMeV are observed with simultaneous measurements of side-scattering emissions that indicate the formation of self-channelfing and self-injection of electrons into a plasma wake, referred to as a ＇bubble＇. The three-dimensional particle-in-cell simulations confirmed multiple self-injection of electron bunches into the bubble and their beam acceleration with gradient of 1.5 GeV/cm.     

Electron Acceleration by Beating of Two Intense Cross-Focused Hollow Gaussian Laser Beams in Plasma

This paper presents propagation of two cross-focused intense hollow Gaussian laser beams(HGBs) in collisionless plasma and its effect on the generation of electron plasma wave(EPW) and electron acceleration process,when relativistic and ponderomotive nonlinearities are simultaneously operative. Nonlinear differential equations have been set up for beamwidth of laser beams, power of generated EPW, and energy gain by electrons using WKB and paraxial approximations. Numerical simulations have been carried out to investigate the effect of typical laser-plasma parameters on the focusing of laser beams in plasmas and further its effect on power of excited EPW and acceleration of electrons. It is observed that focusing of two laser beams in plasma increases for higher order of hollow Gaussian beams,which significantly enhanced the power of generated EPW and energy gain. The amplitude of EPW and energy gain by electrons is found to enhance with an increase in the intensity of laser beams and plasma density. This study will be useful to plasma beat wave accelerator and in other applications requiring multiple laser beams.