Time-resolved measurement technique for pulsed electron beam envelope basing on framing and streaking principle

The time-resolved electron beam envelope parameters, including cross sectional distribution and beam centroid position, are very important for the study of beam transmission characteristics in a magnetic field and for verifying the rationality of the magnetic field parameters employed. One kind of high time-resolved beam envelope measurement system has recently been developed, constituted of a high-speed framing camera and a streak camera.It can obtain three panoramic images of the beam and time continuous information along the given beam profile simultaneously. Recently obtained data has proved that several fast vibrations of the beam envelope along the diameter direction occur during the front and the tail parts of the electron beam. The vibration period is several nanoseconds. The effect of magnetic field on the electron beam is also observed and verified. Beam debugging experiments have proved that the existing beam transmission design is reasonable and viable. This beam envelope measurement system will establish a good foundation for beam physics research.     

Electron beam halo formation in high-power periodic permanentmagnet focusing klystron amplifiers

Electron beam halo formation is studied as a potential mechanism for electron beam losses in high-power periodic permanent magnet focusing klystron amplifiers. In particular, a two-dimensional (2-D) self-consistent electrostatic model is used to analyze equilibrium beam transport in a periodic magnetic focusing field in the absence of a radio frequency (RF) signal, and the behavior of a high-intensity electron beam under a current-oscillation-induced mismatch between the beam and the periodic magnetic focusing field. Detailed simulation results are presented for choices of system parameters corresponding to the 50-MW, 11.4-GHz periodic permanent magnet (PPM) focusing klystron experiment performed at the Stanford Linear Accelerator Center (SLAC). It is found from the self-consistent simulations that sizable halos appear after the beam envelope undergoes several oscillations, and that the residual magnetic field at the cathode plays an important role in delaying the halo formation process     

Formation and focusing of electron beams in an electron-optical system with a plasma emitter placed in a magnetic field

The configuration and strength of a magnetic field are calculated in the regions of electron generation, acceleration, and transport in the electron-optical system of the plasma electron source. A magnetic field necessary for discharge initiation and maintenance is generated with a permanent magnet placed in a discharge chamber. It is shown that the magnetic field strength and configuration in these regions can be considerably varied by appropriately choosing the materials of electrodes forming the magnetic circuit. It is found that the beam focusing can be significantly improved by producing a quasi-uniform magnetic field in the electron-optical system of the plasma electron source.     

Scattering of a Bounded Electron Beam by Plasma Waves which are Self-Consistently Excited by the Beam

The nonlinear stage of the beam plasma instability of a bandlike electron beam in unbounded plasma is examined. It is shown that such an interaction is responsible for the extreme beam electron scattering that can be observed in experiments in the absence of an external magnetic field.     

Influence of the longitudinal magnetic field in the accelerating gap on the limiting parameters of a plasma electron source operating in the forevacuum pressure range

Results are presented from experimental studies of the influence of the longitudinal magnetic field in the accelerating gap on the emission current, accelerating voltage, and maximum gas pressure in a plasma electron source generating a continuous electron beam in the forevacuum pressure range. It is shown that the magnetic field in the beam-formation region stabilizes the emitting boundary of the plasma in the accelerating gap, thereby considerably improving the source parameters.     

束流发射度对太赫兹微电真空折叠波导行波管性能的影响

采用理论分析与数值模拟相结合的方法,分别对140,220和345 GHz折叠波导行波管中的束流发射度的影响因素及其对直流导通率的影响进行了分析,总结了发射度随频率、结构参数和电子束参数的变化规律。研究发现,在太赫兹频段束流发射度直接决定着聚焦磁场的选取设计, 是表征太赫兹频段束流品质的一个重要参量。     

Effect of the anode-current magnetic field on the motion of electrons in a triode with a virtual cathode

The effect of the anode-current magnetic field on the electron motion in a triode with a virtual cathode is considered. It is shown that the anode-current magnetic field influences the oscillation period and trajectories of electrons. The condition of self-isolation of the electron beam is investigated as a function of the diode parameter. It is shown that the displacement of the beam electrons under the action of the anode-current magnetic field leads to a decrease in the electron phase modulation and an increase in the spread in the electron oscillation amplitude; as a result, the generation efficiency of microwave radiation decreases.     

Space charge effects in a gyrotron employing a solid electron beam

The influence of space charge forces on the performance of a single cacity gyrotron oscillator which uses a solid electron beam was investigated. It was found that space charge effects cause a large efficiency degradation as the beam current is increased, if the other experimental parameters are unchanged. A small increase in the magnetic field, however, can restore the efficiency to higher values.This research was supported by the U.S. Office of Naval Research.     

Improvement of the helical electron beam quality and the gyrotron efficiency by controlling the electric field distribution near a magnetron injection gun

A technique for controlling the electric field distribution near the cathode of a magnetron injection gun is developed. The feasibility of improving the quality of a helical electron beam by optimizing the electric field distribution in a pulsed 4-mm-wave gyrotron is studied theoretically and experimentally. Field distributions are obtained that minimize the electron velocity spread in the beam, coefficient of electron reflection from a magnetic mirror, and intensity of parasitic low-frequency oscillations. It is demonstrated that the gyrotron efficiency can be increased through a rise in the beam quality at the optimized electric field distribution.     

Parameters of the Plasma Sheet Generated by a Sheet Beam in the Range of Forvacuum Pressures

Results of experimental investigations into the spatial distribution of the parameters of the plasma (electron concentration and temperature) generated by a sheet beam with energy up to 2 keV in argon at pressures from 6 to 9 Pa are presented. The electron beam was produced by a source with a plasma cathode specially designed for emission of beams in the range of forvacuum pressures. It is demonstrated that the character of distribution of the plasma parameters is caused by the corresponding distribution of the electron current density over the beam cross section, and the plasma parameters themselves also noticeably depend on the gas pressure and the magnetic field. A model of ionization processes that provides satisfactory agreement between the calculated and experimental dependences is suggested.     

Stimulated emission of an electron in a magnetic field in the n = 1 level

This paper considers the influence of the external magnetic field of a wave on polarization of an electron in a magnetic field. It is shown that when the anomalous magnetic moment of the electron is taken into account, the actual polarization of an electron beam in the n = 0 state can be obtained.Translated from Izvestiya VUZ. Fizika, No. 12, pp. 97–100, December, 1971.     

Theory and simulation of an 85 GHz quasioptical gyroklystron experiment

The linear theory used to design a two-resonator 85 GHz quasioptical gyroklystron with a nonuniform magnetic field is presented. It is shown that a tapered magnetic field in the prebunching resonator has a relatively small effect on the electron bunching parameter. The effect of velocity spread of the electron beam can be minimized by adjusting the magnetic field strength in the two resonators. Measured amplifier performance is in good agreement with calculations from the nonlinear multimode simulation code. Gyrophase bunching of the electrons is preserved over the long drift region (30 radiation wavelengths) even though no attempt has been made to minimize the velocity spread of the beam.     

铁磁性加载复合管壳电子注聚焦性能的研究

大功率行波管通常利用复合管壳提升高频系统的集成度和散热特性。宽带行波管采用复合管壳高频制造工艺时,由于加载翼片含有铁磁性材料(纯铁)使得聚焦系统的横向磁场分量变大,径向和角向磁场分量呈非均匀性,电子注聚焦困难。本文研究了周期永磁聚焦系统横向磁场产生的原因并建立理论模型,并对磁场分量和其对电子注形态的影响进行了仿真,仿真结果与理论计算结果一致。根据横向磁场分布模型对加载翼片的形状和数量进行优化仿真,结果表明9片齿形加载翼片方案可在保持慢波电路参数的同时,降低聚焦系统的横向磁场分量,改善电子注聚焦效果。     

Parameters of the electron beam in a betatron with radial comb-type poles

Expressions for the vector potential and components of the magnetic field induction vector of a betatron with radial comb-type poles are derived. The dynamics of the electron beam in the electromagnetic betatron field is investigated in the process of electron injection and acceleration. It is demonstrated that the azimuthally varying field engender beam beats. However, the amplitudes of beam particle oscillations during acceleration do not exceed their values estimated from the symmetric azimuthal component of the betatron magnetic field induction. The energy spectrum of accelerated electrons is not described by a normal law. In the electron energy spectrum, the relative number of electrons whose energy exceeds the average value is large. Application of poles with radial combs improves the efficiency of electron capture in acceleration. Results of investigations can find application in the development and adjustment of electron beam accelerating systems. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 27–34, October, 2005.     

Generation of high-current relativistic electron beams with stable (for a microsecond) parameters using explosive emission cathodes

Cold explosive emission cathodes, in which a plasma serves as an emitting surface, are used to generate relativistic electron beams with a high current density in a magnetic field. The plasma parameters change within a microsecond, thereby significantly changing the geometry of the electron beam. This paper is a review of techniques for stabilizing the geometry of microsecond high-current relativistic electron beams. It is shown that only a transverse-blade explosive emission cathode in a magnetically insulated diode can generate such beams (500 keV, 3 kA) the current density profile and electron trajectory pitch factor of which remain constant for a microsecond.     

Numerical investigation of radio-frequency negative hydrogen ion sources by a three-dimensional fluid model

A three-dimensional fluid model is developed to investigate the radio-frequency inductively coupled H2 plasma in a reactor with a rectangular expansion chamber and a cylindrical driver chamber, for neutral beam injection system in CFETR. In this model, the electron effective collision frequency and the ion mobility at high E-fields are employed, for accurate simulation of discharges at low pressures(0.3 Pa–2 Pa) and high powers(40 k W–100 k W). The results indicate that when the high E-field ion mobility is taken into account, the electron density is about four times higher than the value in the low E-field case. In addition, the influences of the magnetic field, pressure and power on the electron density and electron temperature are demonstrated. It is found that the electron density and electron temperature in the xz-plane along permanent magnet side become much more asymmetric when magnetic field enhances. However, the plasma parameters in the yz-plane without permanent magnet side are symmetric no matter the magnetic field is applied or not. Besides, the maximum of the electron density first increases and then decreases with magnetic field, while the electron temperature at the bottom of the expansion region first decreases and then almost keeps constant. As the pressure increases from 0.3 Pa to 2 Pa, the electron density becomes higher, with the maximum moving upwards to the driver region, and the symmetry of the electron temperature in the xz-plane becomes much better. As power increases, the electron density rises, whereas the spatial distribution is similar. It can be summarized that the magnetic field and gas pressure have great influence on the symmetry of the plasma parameters, while the power only has little effect.     

周期永磁磁场导引环形强流电子束研究

 利用磁场有限元法，计算了周期性布置的永磁铁内的磁场；利用流体模型分析了作用在束电子上的力并导出了改进Matheiu函数形式的径向力方程；利用2.5维PIC程序研究了束传输的物理过程。计算发现强流相对论电子束的稳定传输与束等离子体密度、束平衡位置、磁场的强度、磁场周期长度等有关。研究认为利用周期性永磁场导引数kA的环形电子束，使之稳定传输是可能的。     

Net acceleration of high-energy electrons by net inverse Bremsstrahlung of a laser wave in a uniform magnetic field and a transverse undulating magnetic field

The nonzero net dc force acting on relativistic beam electrons traveling in a uniform magnetic field, a laser wave, and transverse undulating magnetic field (magnetic wiggler) is calculated by using quantum-kinetics in accordance with the correspondence principle. It is found that the average of this force can be as strong as the Lorentz force of the laser wave in an electron energy region beyong energies for free electron lasing, and decreases linearly with the inverse of the electron energy far beyond this energy region.     

电磁铁摇摆器磁场的二维数值计算

本文根据泊松方程用数值计算给出了电磁铁摇摆器的二维磁场分布,定量地讨论了磁极形状、磁隙大小、周期长短和电流大小等因素对峰值磁场强度的影响,重点讨论了如何根据二维磁场分布选择磁极形状才能提高峰值磁场强度和抑制磁饱和的问题。将计算的二维磁场分布和摇摆器磁场的理想波形相比较,可以帮助我们确定进入摇摆器的束流半径应该控制的范围。在对电磁铁摇摆器磁场二维数值计算的基础上,还探讨了适用ATA电子束的PALADIN摇摆器用于ETA电子束带来的结构设计和材料选择等问题。     

On possibility of measurement of the electron beam energy using absorption of radiation by electrons in magnetic field

A possibility of precise measurement of the electron beam energy using absorption of radiation by electrons in a homogeneous magnetic field for electrons of high energy in the range up to a few hundred GeV, was considered earlier. In this paper, with the purpose of experimental checking of this method in the range of several tens MeV of electrons energies, a possibility of measurement of absolute energy of the electron beam with a relative accuracy up to 10^?4, is considered. We take into account influence of the laser beam diffraction, of the spread of electrons over energies, and of the length of formation of radiation absorption in the process of electron beam energy measurement. The laser wavelength and the length of the magnet are chosen depending on the length of photon absorption formation. It is found that the kinematical restrictions on the photon absorption process lead to the selection in angles of propagation of photons, which can be absorbed by the beam electrons. It is shown that parameters of the electron beam will noticeably not vary during the measurement of the energy.