Equivalence of periodic magnetic field to uniform magnetic field in electron beam focusing

The general solution of the electron trajectory equation in a periodic magnetic field is derived in the form of series expansion, assuming laminar electron flow and small perturbation. It is concluded that if the cathode is not very heavily immersed in a magnetic field, beam focusing by a periodic magnetic field would be almost equivalent to that by a uniform magnetic field except near the unstable region. Under these restrictions, each focusing system would give almost the same beam ripple (in magnitude and phase) under the same injection conditions into the focusing system. It is also found that the first stable region of beam perturbation in the periodic magnetic field becomes narrower as the flux threading the cathode increases or the period of the magnetic field decreases, as far as linearization of the path equation is possible.     

浸没流多透镜多注电子光学系统的模拟研究

该文采用先2维后3维的计算方法,对L波段高峰值功率多注速调管电子光学系统进行了模拟设计。采用均匀场浸没流多透镜聚焦系统对电子注进行聚焦,获得了通过率100%,填充因子55%,特性良好的旁轴电子注。模拟计算表明,多透镜系统可有效调整电子注平衡半径,电子枪区均匀场可有效调整电子注波动性及层流性,聚集系统可在阴极磁感应强度为0.001~0.01 T,主磁场为0.06~0.13 T的范围内实现对旁轴电子注的良好聚焦。     

碳纳米管冷阴极Pierce电子枪

为发展场致发射冷阴极毫米波电真空辐射源器件, 对利用大面积碳纳米管冷阴极产生大电流、高电流密度电子注的电子光学系统进行了研究.通过在Pierce电子枪阴极表面引入栅网结构, 解决了碳纳米管冷阴极场致发射所需的强电场和电子聚束问题.在碳纳米管冷阴极实验测试数据的基础上, 采用粒子模拟软件对上述电子光学系统进行了仿真.研究了栅网对注电流、注腰半径和电子注散射的影响, 分析了阳极电压和外加轴向磁场对电子注的聚束作用.优化后的仿真结果表明在阴极发射面为3.03 cm2时, 该电子光学系统能够产生210 mA、60 kV, 电流密度为6.7 A/cm2, 最大注半径为1mm的电子注.     

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。     

Electron Beam Optics System PIC Simulation for MMW TWTs

The basic feature and design method of MMW TWTs electron optics are analyzed in this paper. With the increasing area convergence ratio of the electron gun in TWTs, the initial thermal velocity of electrons at cathode and the non-magnetic shielded effect can no longer be neglected. It brings new challenge for the design and simulation of MMW TWTs electron optics. A method of investigation the beam DC characteristics is described using particle-in-cell (PIC) simulation and incorporate electron beam optics model integrated electron gun with periodic permanent magnetic focusing system. It is valuable for achieving the goal of “first-pass design success” and the electron optics engineering design and optimization.     

Hollow-beam focusing with electrostatic and periodic magnetic fields

A new method of focusing a hollow cylindrical electron beam is presented. The focusing system consists of a cylindrical center conductor inside the beam, a cylindrical outer conductor enclosing the beam, and a series of periodic magnets outside the tube. A radial electrostatic field between the conductors provides an outward force on the electrons. The periodic magnetic field produces an inward force on the electrons. The inward and outward forces can be adjusted to provide a balance of all the forces acting on the electrons at both boundaries of the beam by choosing the electric and magnetic fields properly. An approximate analysis has been made and is presented which gives necessary design information. A number of curves are presented which are useful in designing focusing systems of this type. Experimental results on a beam tester show that current transmission of over 90 per cent for perveance up to 11 micropervs can be obtained readily. The adjustments are not critical and the performance is very stable.     

A model of the electron-optical system of a finite-width ribbon beam in the case of approximation of the initial rectangular contour by an ellipse

A model of the electron-optical system with straight axis and a finite-width ribbon beam is constructed on the basis of exact solution of partial differential equations describing a narrow relativistic beam in axisymmetric external magnetic field in the case when the initial rectangular contour is approximated by an ellipse. Rotating and nonrotating beams and curved or planar cathode in the case of emission in the T mode are considered.     

A low potential collector employing an asymmetrical electrode in an axially-symmetric magnetic field

A collector for a beam-type tube with an axial magnetic focusing field can be made to operate at a potential near cathode potential without returning secondary electrons, if the beam is deflected and caused to pass an asymmetrical electrode properly positioned in the axially symmetric magnetic focusing field. Collection takes place in a region of radial electric field. Experimental results on such a device indicate successful operation, provided the velocity spread in the beam is not too large.     

Design of a Large Orbit Gyrotron with a Permanent Magnet System

The paper presents results of numerical analysis and outlines the computer-aided design of a novel high-harmonic gyrotron with a beam of electrons gyrating along axis-encircling trajectories. The electron beam is formed by a novel electron-optical system (EOS) based on an electron gun of diode type with thermionic cathode and gradual reversal of the magnetic field. The results of numerical simulations predict satisfactory performance of the EOS and appropriate beam quality parameters. The tube design allows one to install different cavities optimized for excitation of TE_4,1 mode at the fourth harmonic of the cyclotron frequency or TE_3,1 mode at the third one. The target parameters of the device are: frequency about 112 GHz; output power near 1 kW and efficiency of several percent.     

A method to from a rectilinear electron beam with small pulsations for free electron masers

When a solid electron beam is formed by a two-electrode axially-symmetrical gun immersed in uniform axial magnetic field, the anode aperture, cutting off the near-axis part of the beam acts as an electrostatic lens and causes unwanted pulsations of the beam. Initial oscillations of electrons are especially unfavorable for free-electron masers (FEMs), in which they lead to a too large spread in the oscillating and, correspondingly, in the translational velocities of the particles. A method for compensation of the parasitic action of the anode aperture by means of a small correcting coil and formation of an electron beam with minimum pulsations is suggested in this paper. Results of estimations and numerical simulations demonstrating the effectiveness of the method when using it in an electron-optical system of a millimeter wavelengths cyclotron autoresonance maser (CARM) are discussed.     

Electron-beam flow in superimposed periodic and uniform magnetic fields

Theoretical and experimental results are presented on the focusing of an electron beam by means of a magnet structure which produces, along the axis of the beam, a periodic magnetic field superimposed on a uniform field. The relation between space-charge and magnetic-field parameters for minimum ripple is derived. The flow in superimposed uniform and periodic magnetic fields is shown to be degraded from the flow of electrons in a magnetic field which has a sinusoidal variation along the axis. The results indicate the flow conditions to be expected, where such combined fields are unavoidable. The focusing of electron beams in this type of superimposed magnetic field and in Brillouin flow are compared.     

Periodic focusing of beams from partially shielded cathodes

Using both an analog computer and an approximate analytical method, the equation describing the beam shapes which result from a uniform pencil beam of electrons entering a periodic magnetic field has been studied. The investigation has been primarily directed toward beams emergent from ideal cathodes only partially shielded from the magnetic field. Cases of both small and large scalloping have been considered. Curves relating the magnetic field coefficient α and the space-charge coefficient β are presented. A previously proposed relationship between α and β for small scalloping is shown to be inaccurate for large scalloping. Stable solutions for the motion of an electron beam having no thermal velocities are obtained for values of α less than 0.66 and in addition they are also found for some values of α greater than 0.66.     

Modeling a subterahertz traveling-wave tube with a slow-wave structure of the double grating type and a sheet electron beam

A traveling-wave tube of the millimeter range belonging to the short-wavelength region with a sheet electron beam and a slow-wave structure of the double grating type is studied. Its dispersion characteristics and coupling impedances for various spatial harmonics are calculated. The issues of design of the electron-optical system are discussed. The focusing of a sheet electron beam with a high current density by a uniform magnetic field is modeled.     

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.     

基于Spindt冷阴极的行波管电子枪设计

针对X波段小型化Spindt冷阴极螺旋线行波管进行了电子枪设计.基于皮尔斯型电子枪结构,联合PPM高频聚焦系统,以电子注聚焦特性为优化目标,采用CST粒子工作室对电子枪结构和工作参数进行了优化设计,获得了 30 mA工作电流下电子注填充比为0.68的良好电子注聚焦.在此电子枪结构和高频结构下,分析了特定电流下电子注聚焦...     

Electron-beam defocusing due to high-intensity RF fields

The electric fields associated with a "slow" electro-magnetic wave propagating along an electron beam will modulate this beam; the axial component of field will produce the usual "bunching," while the radial component will cause periodic perturbations in the radius of such an electron beam. This paper presents the results of analytical and experimental studies in an attempt to explain certain features of this defocusing effect of intense RF fields on the beam in a traveling-wave tube. In particular the effect of cathode flux on the RF defocusing of a beam in Brillouin flow is treated.     

Dynamic defocusing of electron beams in high-power helical traveling-wave tubes with length-dependent dispersion

Dynamic defocusing in a wideband helical traveling-wave tube (TWT) with an output power of 1.5–2.0 kW in the continuous-operation mode is analyzed. The TWT contains fragments with normal and anomalous dispersion of the phase velocity. It is demonstrated that the TWT output characteristics can be improved and the TWT stability against self-excitation on the backward wave can be increased with the use of appropriate values of parameters of the electron-optical system that forms a converging axially symmetric beam focused by a periodic permanent-magnet focusing system.     

Intense Sheet Electron Beam Transport in a Uniform Solenoidal Magnetic Field

In this paper, the transport of intense sheet electron beams in a uniform solenoidal magnetic field in high-power vacuum electronic devices is theoretically examined with the 3-D beam optics code MICHELLE. It is shown that a solenoidal magnetic field can be an effective transport mechanism for sheet electron beams, provided the beam tunnel is matched to the beam shape, and vice versa. The advantage of solenoidal magnetic field transport relative to periodic magnetic transport resides in the feasibility of transporting higher current density beams due to the higher average field strength achievable in practice and the lower susceptibility to field errors from mechanical misalignments. In addition, a solenoidally transported electron beam is not susceptible to voltage cutoff as in a periodic magnetic focusing system; hence, device efficiency is potentially higher.     

TWO-DIMENSIONAL NUMERICAL SIMULATION OF LOW FREQUENCY OSCILLATIONS OF SPACE CHARGE AND POTENTIAL IN THE GYROTRON ADIABATIC TRAP

The development of oscillations of the space charge and potential in the adiabatic trap of a gyrotron between the cathode and the cavity is studied numerically. The PIC method is applied, with the real two-dimensional distributions of the electric and magnetic fields taken into account. Secondary emission is included into the numerical model, as well as such factors as the electron beam space charge, thermal velocities of electrons, and emitter roughness. The value of the trapped space charge as a function of time is calculated. Time dependences of the potential in various cross-sections of the formation system are traced. The amplitudes of its variable component have been found and then the corresponding frequency spectra have been calculated. The process of cathode bombardment is investigated. The energy distribution and time dependence of the current in the electron beam coming to the operating space are found. Some ways to reduce the oscillations of the potential and the space charge are discussed.     

Low convergent confined-flow Pierce gun for a space TWT

An approach for designing an electron gun for a high efficiency, high linearity space traveling wave tube (TWT), has been presented. A low convergent (<10?:?1) Pierce electron gun of beam perveance 0.43?μP has been designed for a high gain, high linearity and high efficiency C-band 60?W Space TWT using in-house developed two-dimensional FDM based gun and collector simulation code PIERCE. In this gun, the first anode (isolated from the ground anode) has been kept nearly 100?V above the ground anode to act as an ion barrier for increasing cathode life and to regulate beam current over the lifetime of the tube. An M-type dispenser cathode of diameter 3.20?mm has been used for cathode loading of less than 1.0?A/cm² and heater wattage around 3.0?W. The magnetic focusing with integral-pole-piece barrel assembly and periodic-permanent magnets (PPM) have been designed using in house developed two-dimensional FDM based code SUNMAG. The practical problem of linking requisite cathode flux to the cathode for confined flow of the electron beam with low convergence factor has been sorted out by gradually increasing the PPM magnetic field. The magnetic field has been increased in steps from the gun and over the first five magnets varying from Brillouin field (B _B) value to twice B _B for achieving the electron beam with scalloping less than 10%. Agreements between the simulated results and the experimental results for the beam current and magnetic field profile have been achieved within 8%. The dynamic beam transmission (under rf operation of the tube) has been achieved better than 98% in the tube.