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.     

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 gun and focusing system for crossed-field traveling-wave tubes

A problem encountered in the design of crossed-field traveling-wave tubes (particularly M-type amplifiers or backward-wave oscillators) is a limitation on current due to the restricted cathode size in the usual gun systems. The scheme considered here incorporates into a crossed-field device the techniques commonly used in O-type devices for designing converging Pierce-type strip-beam guns, which can increase the effective cathode area by perhaps ten times. A design procedure is presented for getting a well-formed beam from such a gun, which is magnetically shielded, through a fringing crossed-field region into the uniform-field region of interaction. An analysis of electron flow through the fringing-field region, including the effect of space charge, is presented. A trajectory equation, solved on a digital computer, yields trajectories for the beam and design curves for various values of the important parameters. The results show the scheme to be feasible. Results are also presented from tests on an experimental, demountable tube used to test the focusing scheme. About 90 to 95 per cent of the current entering the crossed-field region could be focused to the collector, and the system behaved generally as the design predicted. An evaluation of the experimental data showed the scheme to be useful.     

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.     

Magnetically shielded electron–optical system of a continuous gyrotron with an operating frequency of 24 GHz

It is shown that it is possible to use warm solenoids with copper winding screened with ferromagnetic shields in order to reduce the solenoid supply power by a factor of 1.8–2 while retaining the strength of the magnetic field in the working space for continuous gyrotrons operating in a frequency range of 24–30 GHz. The configuration of the shields as well as the shape and location of the correcting solenoids providing an extended (up to 10 wavelengths long) section of a uniform field in the region of the gyrotron cavity have been determined. It has been shown that introduction of an additional cathode coil into the magnetic system reduces the degree of nonadiabaticity of the magnetic field approximately by an order of magnitude and thereby makes it possible to use the magnetron injection gun for formation of a helical electron beam. Optimization of the configuration of the gun electrodes based on the trajectory analysis makes it possible to obtain an electron beam whose parameters are as good as parameters of the electron beams formed in classical adiabatic electron–optical systems of gyrotrons.     

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.     

Focus reflex modulation of electron guns

High resolution and low drive features have been successfully combined in a new type of electron gun for cathode-ray tubes. The gun has a spot-defining aperture of 0.007 inch upon which emission from a large cathode area is concentrated by a retarding electron lens. This unit modulates the beam by electron reflection, while focusing it upon the aperture ("Focus Reflex Modulation"). Immediately ahead of the aperture, a modulated virtual cathode is formed with an emission capability of over four amperes per square centimeter. A1000-microa beam with a 6° divergence is controlled by a signal of 12 volts centered at ground potential. Highlight brigntness of 250 foot lamberts was read at 17,500 volts, while more than 500 lines were resolved on a television test pattern. In more recent forms of the FRM gun,1600 microa are measured in the screen return, out of1800-microa cathode current. This is 88 per cent over-all transmission, using the same defining aperture (0.007 inch). 18 volts of drive signal will completely modulate the above current.     

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.     

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.     

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.     

场致发射阵列阴极电子枪的设计及模拟研究

讨论了微波管用电子枪的一般参数和要求，对于在微波管中应用场发射阵列阴极电子枪的情况作了分析，表明其中存在的主要问题是电子注散焦。通过比较场发射电子注聚焦的几种方法，利用传统电子枪整体聚焦的思想，初步设计了一个场发射阵列阴极电子枪模型，它包括场致发射阵列阴极，一个Whelnelt电极，一个聚焦电极和一个阳极。通过利用Mafia软件对电子注轨迹的模拟计算，对电子枪的聚焦部分进行了改进。     

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...     

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.     

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.     

Electron beams in axially-symmetric crossed fields

M-type traveling-wave tubes use electron beams that drift in crossed electric and magnetic fields. One such tube, the axiotron described by Warnecke and Doehler in 1950, used a hollow beam drifting parallel to the tube axis in a radial electric field crossed by an azimuthal magnetic field. The addition of an axial magnetic field to the azimuthal one adds another degree of complication and flexibility to the beam equations, yet maintains their symmetry about the tube axis. It gives, in effect, a helical magnetic field crossed by a radial electric field. This report examines the behavior of hollow electron beams drifting in laminar flow through fields of the latter configuration. It defines a stability index for electron paths, and four fairly general types of beam. It determines the stability index and the distribution of space charge obtainable in each type as functions of the amplitudes and directions of the fields and drift velocities. In general, the density tends to be greatest at the inner beam radius, but it is possible to approach uniform density in stable beams. This report does not consider beam launching nor the "gun" problem; nor does it consider over-all beam instabilities such as scalloping.     

The effect of space charge on shot noise in crossed-field electron guns

The two-dimensional electronic behavior of the crossed-field potential minimum is analyzed by means of a feedback network which provides a vehicle for understanding the complex phenomena, while allowing quantitatively accurate numerical calculations. The solutions, limited to the low-frequency range where transit time may be neglected, Show shot-noise smoothing as a function of magnetic field and cathode length. For low magnetic fields and short cathodes, the smoothing approaches the results of the North theory for zero magnetic field. It is also shown that if the cathode length is greater than about 11 normalized (Kino) units or 0.55 of the cycloid length for the existing field conditions, an initial perturbation of the emission current will lead to growing fluctuations of the beam current. This instability is considered to be responsible for the observation, in some crossed-field tubes, that the output noise increases when the cathode is heated sufficiently to form a potential minimum in front of the cathode. This criterion for the existence of excess noise is applied to all the experiments for which sufficient data have been published and no disagreement is found.     

A scan-conversion tube utilizing fiber-optics photon transfer

Scan-conversion tubes utilizing fiber-optics photon transfer (FOPT) are currently being developed by the Westinghouse Electric Corporation under contract from the United States Army Electronics Research and Development Laboratory. The tubes consist of three major components: a reading electron gun, a writing electron gun and an interjacent scan-conversion target. The targets consist of a fiber-optics disc coated on one side with a phosphor and on the other with a photoconductor, the reading gun is similar to the low velocity gun of a vidicon and the writing gun is a high velocity cathode-ray tube gun. The majority of targets tested have incorporated a long storage Permachon type photoconductor and a short persistence phosphor; however, other photoconductors and phosphors can be used to perform a variety of video conversions and/or signal enhancements. Operation of these scan-conversion tubes requires only the circuitry normally associated with the driving of a cathode-ray tube and a vidicon; no RF or other type of cancelling circuitry is required to separate the written and read-out signals.     

Computer simulation of the backward-wave distributed-emission crossed-field amplifier

A computer simulation of the backward-wave distributed emission crossed-field amplifier has been achieved with a developmental two-dimensional time-dependent calculation. The model simultaneously treats the entire re-entrant electron stream, the vane RF circuit, the secondary-emitting cathode and the modulator. There is reasonable quantitative agreement with the measured magnetic field, anode voltage, current and RF power. An anomalous low-power mode, unexpected before these simulations, shows an irregular beam that is a possible cause of the low efficiency and the high cathode backbombardment that were measured.     

The effect of tolerances in conical flow Pierce guns II—The perturbed flow in the magnetic field

The first-order perturbations to a beam initially in nonrippling Brillouin flow, which results from several common manufacturing errors in conical flow Pierce guns, are calculated. The manufacturing errors are changes in cathode-anode spacing, changes in cathode curvature, tilt, and transverse displacement of the cathode-focus electrode assembly, and tilt and transverse misalignment of the whole gun to the magnetic field. Errors in cathode-to-focus electrode spacing are not discussed. The tolerances which destroy the rotational symmetry of the gun are shown to cause the smooth beam to perform a helical motion; the tolerances which preserve the symmetry are shown to produce an undulating beam. Using the results of Part I of this paper [1], the magnitudes of individual gun tolerances are related to the effects they produce in the magnetic field. A method of setting limits to the individual gun tolerances is presented and illustrated by calculating tolerances for a gun used in an X-band traveling-wave tube. The calculated tolerances are found to have values which may readily be achieved by careful engineering.