Advanced Numerical and Experimental Investigation for Gyrotrons Helical Electron Beams

The paper presents a modern approach to studies of characteristics of intense helical electron beams (HEBs) for gyrotrons. The essence of the method consists in finding functions of electron distribution with respect to oscillatory velocities in the beam both by numerical simulation and experimentally. Experimental and calculated data for beams with different topologies were compared in different frequency ranges. Evolution of the electron oscillatory velocities distribution function as the beam current grows has been traced. Influence of the reflected electrons on beam parameters has been simulated numerically.     

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.     

Condition for Injection of Intense Relativistic Electron Beams into a Z Pinch

Intense relativistic electron beams have been injected into the plasma of a Z pinch at various times during the formation of the plasma column. If the diameter of the plasma column exceeded a certain value, these beams were found to propagate with a high transport efficiency when injected either into the collapsing current sheet of the Z pinch or into the expanding plasma column after its diameter had reached a minimum. However, when the diameter of the plasma column is smaller than this critical value, the relativistic electron beam does not propagate. Instead, it continues to diverge until it strikes the glass wall of the Z pinch tube.     

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.     

High-Harmonic Gyrotrons with Axis-Encircling Electron Beams at IAP RAS

Radiophysics and Quantum Electronics - The Institute of Applied Physics of the Russian Academy of Sciences has for many years been developing sub-terahertz and terahertz large-orbit gyrotrons that...     

Forming of Space Charge Wave with Broad Frequency Spectrum in Helical Relativistic Two-Stream Electron Beams

We elaborate a quadratic nonlinear theory of plural interactions of growing space charge wave(SCW) harmonics during the development of the two-stream instability in helical relativistic electron beams. It is found that in helical two-stream electron beams the growth rate of the two-stream instability increases with the beam entrance angle. An SCW with the broad frequency spectrum, in which higher harmonics have higher amplitudes, forms when the frequency of the first SCW harmonic is much less than the critical frequency of the two-stream instability.For helical electron beams the spectrum expands with the increase of the beam entrance angle. Moreover,we obtain that utilizing helical electron beams in multiharmonic two-stream superheterodyne free-electron lasers leads to the improvement of their amplification characteristics, the frequency spectrum broadening in multiharmonic signal generation mode, and the reduction of the overall system dimensions.     

Formation of Intense Quasicylindrical Charged-Particle Beams

Physics of Particles and Nuclei Letters - 2D and 3D problems of the formation of intense relativistic charged-particle beams are discussed for different geometrical configurations. Both the exact...     

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.     

渡越辐射在强流电子束诊断中的应用

文中描述了渡越辐射用于束流诊断的理论依据,介绍了利用渡越辐射对18MeV,2.7kA的强流脉冲电子束进行诊断的实验方案,介绍了在强流束测量中遇到的困难和解决方法.实验中获得了渡越辐射的特征图案,并对特征图案进行了分析,得到了测量时应该使用偏振片的结论.据此,利用渡越辐射测量了强流脉冲束的剖面、能量、发散角.并采用渡越辐射与切伦科夫辐射相结合的方法，用切伦科夫辐射测量束剖面,用渡越辐射测量能量和发散角,在同一次实验中获得了强流脉冲束的归一化发射度.     

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。     

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.     

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.     

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.     

A Potential Method for Diagnostics of Subfemtosecond Electron Beams Using Coherent Optical Transition Radiation

Russian Physics Journal - Coherent transition radiation (CTR) is widely used in determining the longitudinal e-beam dimensions in the accelerator technology applications. In this study, the CTR...     

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.