Investigation of a Convergent Flow Crossed-field Gun†

An abbreviated version of the Kino short gun has been developed for use as a crossed-field beam injection system. The gun is terminated at a plane where the theoretical average space-charge density, beam location and beam thickness are approximately equal to the corresponding Brillouin quantities for the given anode-sole region conditions. The theoretical design was subjected to a digital computer analysis with the results indicating some intersection of the electron trajectories, although the beam configuration was essentially as predicted. Modification of the cathode ramp electrodes resulted in either laminar flow or uniform cathode emission, but not simultaneously. Experimental investigations carried out in a beam analyser indicated better than 90% transmission of cathode current to the collector for theoretical operating conditions. Beam profile measurements verified that the beam entered the anode-sole region with the desired thickness and at approximately the Brillouin beam location. Furthermore, the undulation of the beam in the anode-sole region was minimal when the magnetic field was set at the optimum value. In general, the abbreviated Kino gun was demonstrated to be a good beam-launching system for crossed-field injected-beam devices.     

A new type of cathode-ray tube with a crossed-field gun

This paper introduces a new type of cathode-ray tube with a crossed-field electron gun which produces an electron beam in a region where a nonuniform magnetic field and an electric field cross perpendicularly. The new configuration gives increased freedom in the design of crossed-field guns. As a result, a long, directly heated cathode can be readily applied to a gun structure which makes high perveance and instant operation possible with much improved cathode heating efficiency. The new gun provides ion trap action by virtue of a magnetic field which separates ions from electrons due to the difference in their masses. A new type of cathode-ray tube using this gun not only demonstrates these features but also requires relatively low operational voltages for beam acceleration and control electrodes. The paper includes an analysis of electron motion in a crossed field with a nonuniform magnetic field. It also shows practical configuration of electrodes and current characteristics of the gun.     

Amplitude and frequency modulation using a wide dynamic range injected-beam crossed-field gun†

Methods for amplitude modulation and frequency modulation of injected beam crossed-field tubes using a wide dynamic range crossed-field gun (Sidhu and Wadhwa 1967) are described. This gun has the property that by properly adjusting the electric fields in the two regions of the transformer section, the electron beam can be injected into the interaction region at any desired level, with a fixed injection velocity or the velocity of injection can be varied over a wide range at a fixed injection level. The properties of injection level variations and injection velocity variation can be utilized to produce amplitude modulation and frequency modulation in injected beam crossed-field tubes.

The beam is injected optimally into the interaction region as desired, without any cycloid formation under conditions of fixed magnetic field. The flexibility of the gun to give variable current and inject the beam optimally into the interaction region under the conditions of fixed magnetic field, can also be used for amplitude modulation purposes.     

The experimental characteristics of a wide dynamic range crossed-field gun

This paper briefly describes the experimental verification of the properties of a wide dynamic range crossed-field gun [1]. This gun, which is a combination of a Kino short gun (or it could be a Kino long gun) and a two-section transformer region, can be used to inject electron beams (with cathode current density varying over a wide range) into the interaction region under optimum conditions and under conditions of a fixed magnetic field. The beam injection level and its injection velocity can also be varied over a wide range by suitably adjusting the electric fields in the two sections of the transformer. The fabrication of the experimental tube is also briefly described.     

Noise-figure calculations for crossed-field forward-wave amplifiers

The problem of finding an adequate model for derivation of noise-figure expressions for crossed-field forward-wave amplifiers is investigated. The modified Llewellyn-Peterson equations are used for the portion of the beam near the cathode. Four waves, two cyclotron waves and two space-charge waves, are used for the space connecting the gun and interaction region. Noise-figures are found by considering five waves in the interaction region. The results are very close to those found when only the space-charge waves are considered in the development of the equations for both drift and interaction regions. A matrix, like the space-charge-wave matrix for O-type beams, giving the transformation of beam fluctuations along a drifting, crossed-field stream including the effects of four waves is presented. Expressions for fluctuations of transverse velocity and beam center of gravity are derived to account for all the excitation quantities which are believed to be important in crossed-field amplifiers. The transformation of fluctuations of beam position, or center of gravity, along an accelerating stream is derived. Calculated values of noise figures are far in excess of experimental values. The reasons for the discrepancies are discussed.     

A new evaluation method of electron optical performance of high beam current probe forming systems

A new numerical simulation method is presented for the electron optical property analysis of probe forming systems with point cathode guns such as cold field emitters and the Schottky emitters. It has long been recognized that the gun aberrations are important parameters to be considered since the intrinsically high brightness of the point cathode gun is reduced due to its spherical aberration. The simulation method can evaluate the 'threshold beam current I(th)' above which the apparent brightness starts to decrease from the intrinsic value. It is found that the threshold depends on the 'electron gun focal length' as well as on the spherical aberration of the gun. Formulas are presented to estimate the brightness reduction as a function of the beam current. The gun brightness reduction must be included when the probe property (the relation between the beam current l(b) and the probe size on the sample, d) of the entire electron optical column is evaluated. Formulas that explicitly consider the gun aberrations into account are presented. It is shown that the probe property curve consists of three segments in the order of increasing beam current: (i) the constant probe size region, (ii) the brightness limited region where the probe size increases as d approximately I(b)(3/8), and (iii) the angular current intensity limited region in which the beam size increases rapidly as d approximately I(b)(3/2). Some strategies are suggested to increase the threshold beam current and to extend the effective beam current range of the point cathode gun into micro ampere regime.     

The design and performance of grid-controlled, high-perveance electron guns

The focusing electrode and a probe projecting through the cathode serve as control electrodes for the current from a convergent-beam electron gun. The principal advantage of this type of "grid" is that there is no interception of the high-current-density beam by the probe-grid. This paper presents the design procedure and experimental results for typical probe-gridded guns. The design procedure is used to obtain the desired perveance, beam diameter, and approximate laminar electron flow. The probe geometry that results in a minimum beam distortion is discussed. The range of values of amplification factor obtainable and the influence of probe geometry on this factor are discussed. The magnetic field required for focusing the beam from a probe-gridded gun is compared with that required for perfect laminar flow and for focusing the beam from a nongridded gun of similar design. An electrolytic tank in conjunction with an analog computer was used to plot electron trajectories, with the effect of space charge included, for the probe-gridded gun and a similar nongridded gun. A comparison of the electron optics of the gridded and nongridded gun is made. Electrical breakdown and beam current during the interpulse time are problems considered. Methods used to minimize electrical breakdown and interpulse beam current are presented. Several models of probe-gridded guns were constructed. The measured characteristics of these guns demonstrate that the advantages of grid control can be obtained with only a minor effect on gun perveance and beam focusing.     

Experiments with a new type adiabatic crossed-field gun

In this paper experiments with a "long" crossed-field gun, designed by a method given by Kino, are described. This gun yielded the predicted value of current, but the other characteristics of the beam were not in accordance with the results of the theory. Experiments were carried out from which it may be concluded that there are RF instabilities present in the beam, instabilities which grow in the drift region and are generated at the cathode. The rate of growth of these instabilities is of the same order as the rate of growth of RF fields given by the theory of McFarlane and Hay.     

A design method for crossed-field electron guns

A design method for crossed-field guns based on a space-charge-flow solution in crossed fields is given. By using the method of analytic continuation in the complex plane, it is shown that it is possible to find the exact form of the electrodes required The design results in a gun similar to the French "short gun" with the great advantage that the current emitted from the gun and the current density at the cathode can be predicted. It is also shown that by making certain approximations to the exact space-charge-flow solution, a new type of gun can be designed, a "long gun" which can have extremely high convergence. The theory for this latter gun is extremely simple and the electrode shapes can be given entirely in analytic form.     

Direct synthesis of crossed-field electron guns—A novel gun for producing Brillouin flow

A direct approach to the synthesis of crossed-field electron guns is presented. An iterative approximation to the desired beam form is achieved by application of the paraxial ray equation alternatively solving for potential and curvature along the beam while maintaining certain end-point conditions and the desired convergence pattern. When sufficient accuracy is obtained, polynomial approximations are used to express shapes of the trajectories and the electric fields along the beam edges in analytic form. The electrodes to produce the necessary electric fields along the beam edges are calculated by Kirstein's method. A conformal transformation is used to transform the beam edge into the real axis of a complex plane and analytic continuation of a suitable complex potential function is employed to find equipotential lines. These are transformed back into the plane of real coordinates and are surfaces along which electrodes can be placed. A novel short gun which produces a Brillouin beam has been designed using the iterative approach. The availability of beam curvature as a variable has made it possible to find an electrode system which controls the transition from the cathode-region flow characteristics used in Kino's short gun to a drift Brillouin beam. Detailed experimental evaluation of the gun reveals that the beam characteristics are in good agreement with those predicted theoretically.     

The design and performance of a magnetron-injection gun

The space-charge flow solutions described by Kino and others in connection with the crossed-field carcinotron gun can be generalized to form the basis of a magnetron-injection gun design suitable for the production of hollow electron beams. In the first part of the paper this generalization is described. From the resulting flow it is possible to determine by an approximate method the electrodes to produce a gun of desired perveance with nearly uniform current density at the cathode. This technique has been used to design guns having ratios of cathode length to a diameter considerably greater than unity. The close agreement between the results obtained on several experimental guns and the theoretical predictions is described, along with the effect of departures from the prescribed fields given by the design method.     

An Iron-Free Magnetron-Injection-Gun for a 28GHz, 200kW Gyroklystron Amplifier

A design study of a double-anode magnetron-injection-gun is performed to incorporate the electron gun into a high power 28GHz gyroklystron amplifier operating at 70kV and 8.2A. The electron gun is designed to be used in a tapered magnetic field in the cathode region produced from an iron-free superconducting magnet. An electron trajectory code predicts a beam axial velocity spread of 5.9% at α = 1.5, 70kV, 8.2A and 10.4kG, which is a high quality electron beam suitable for the high gain, high efficiency, five-cavity gyroklystron amplifier. The successful design of the high quality electron gun is attributed to a longer gap between the modulating anode and the grounded anode compared with the case of the first 28GHz electron gun built with an iron enclosed electromagnet.     

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...     

Improved Computer Program for Magnetron Injection Gun Design

Gyrotron has received extensive attention owing to its high-power capability, especially when the wavelength shrinks below the millimeter-wave range. The electron beam of a gyrotron is typically generated by a magnetron injection gun (MIG). For high cathode current density, the MIG may operate in a region that combines temperature limited and space-charge limited emissions. An improved computer program for electron gun design is appropriate for MIGs that operate between space-charge limited and temperature limited emission. Moreover, the initial input formation of the program resembles that of the EGUN code. Analysis of a Pierce electron gun and MIGs reveals that the stimulated beam current appears consistent with the measured results. However, EGUN simulation results in which the cathode emitters of MIGs are chosen for the temperature limited emission differ from those of our simulation results. This difference is most likely owing to that the initial emitting energy can not be completely described in the EGUN simulation. Finally, the improved computer program is used to design a MIG for a Ka-band, TE₀₁ mode gyro-TWT.     

关于磁控注入式电子枪的噪声问题

磁控注入式电子枪能提供高导流系数的电子注,可应用于大功率微波管中。但是,通常认为这种电子枪属于交叉场型的,具有交叉场器件固有高噪声的特性。这使它的应用受到了限制。 有两个实验打破了上述这种看法。1962年C波段低噪声行波管应用磁控注入式电子枪获得了3.1dB的噪声系数。1965年S波段中功率前向波放大器获得了3.5dB的噪声系数。但这些器件均限于中小功率范围,阴极长度很短,即阴极长径比很小的情况;而对于大功率管中使用的磁控注入式电子枪,能否获得足够小的噪声系数的问题,尚有待于进一步深入研究。 本文简要讨论了影响大功率微波管中磁控注入式电子枪噪声的主要因素以及通过改变阴极区磁场分布的方法来减小噪声的实验结果。     

Transformation of fluctuations along accelerating crossed-field beams

Equations are derived to express the ac potential difference and the transformation of fluctuations of velocity and current between two arbitrary planes along an accelerating crossed-field electron stream. The system of equations, after being simplified by the assumption of zero total ac current, is applied to the special cases of the temperature-limited diode, the space-charge-limited diode, and a diode in which the beam enters with appreciable average velocity. Finally, the open-circuit equations are applied to an approximate model of a beam in a crossed-field electron gun. A new mechanism of growth, peculiar to the crossed-field beam, is discussed as a possible explanation of the observed large sole current in beam-type magnetron amplifiers and related devices.     

毫米波带状注电子枪的设计方法

利用理论分析和仿真模拟相结合的方法对带状电子注的产生进行了系统的研究,并提出了一种带状注电子枪的设计方法.首先通过理论分析,提出了一种计算带状注电子枪结构参数的迭代算法,即根据注电压、注电流、电子注注腰处半厚度、阴极半厚度和阴极宽度,计算出带状注电子枪的阴极柱面半径、阴阳极间距、阳极柱面半径和射程等主要参数;在此基础上,通过仿真模拟,为毫米波真空电子器件设计了一种带状注电子枪.     

脉宽大于100微秒的强流大截面电子枪

在CO_2激光器的研究过程中,发现利用普通技术放电,在振动激发比较有效的E/N下,不能产生适当的电离。这两者往往是矛盾的,这就导致人们寻求在最佳的E/N下能产生适度电离的技术,即把电离和激发分开控制的技术。美国阿符科公司首先提出了电子束控制主放电的技术。 目前就电子束的激励方法有电子束控制放电用的电子枪和电子束直接激发激光介质用的电子枪。就产生电子束的方式有热阴极电子枪、冷阴极场致发射电子枪和等离子体电子枪。     

A wave treatment of the continuous cathode crossed-field amplifier

The continuous cathode crossed-field amplifier, a device characterized by high eificiency and low phase pushing, is considered in terms of wave theory. Based on analytical treatments that have appeared in the literature, a plasma propagation constant is postulated and correlated with observed experimental results. From this, a qualitative concept of mode coupling is dxawn which has proven to be of great value in understanding crossed-field devices and in predicting the characteristics of newly designed tubes. Following a brief section devoted to the crossed-field diode, the experimental observations which led to the theory are presented, culminating in a coupling-of-modes picture of the interaction which is similar to the familiar beam tube treatment. Relationships necessary for checking the theory are given and attention is paid to several important observations affecting design.     

On the performance of high perveance electron guns

A design of high perveance electron gun has recently been proposed by Müller. An experimental investigation has been made of the electron beams produced from: 1) a gun designed directly from Müller's charts, and 2) a gun whose design is a modification of the Müller design to make it more suitable for high-voltage operation. The perveance in each case was about 2 × 10^-6. The distribution of the current density and the profile of the beam were examined, either by allowing the beam to fall on a plate coated with carbon, or by measuring the current passing through a pinhole in a screen which could be moved across the beam at a number of axial positions. Electrostatic experiments showed that the beams were initially annular, but further along the axis the current density became highest at the center. This is attributed to crossing trajectories resulting from lens aberrations in an anode aperture whose diameter is comparable with the cathode-anode spacing. With magnetic focusing, the current density distribution across the beam varied periodically along the axis to an extent which depended critically on the magnetic field conditions in the accelerating region of the gun.