Computer experiments on electron guns

Computer techniques for analyzing an axially symmetric or two-dimensional electrode system with an emitting surface can be used to obtain cathode current density distribution, beam minimum radius and its location, as well as possible electrode current interception. Here, comparison is made of available experimental data from two axially symmetric Pierce-type guns. The choice of the two axially symmetric Pierce-type guns was made for their different value of PV/T ratio, an invariant for transverse scaling. One of them has a low ratio of PV/T(approx 0.1 times 10^{-6}), which signifies considerable beam spread due to the effects of the Maxwellian velocity distribution of the thermal electrons leaving the cathode. The other gun has a high perveance of2 times 10^{-6}, and thus relatively high PV/T ratio where beam spreading is mainly due to space-charge forces alone. Good agreement with experimental data is shown. Computer techniques of this type can be a valuable tool for diagnostic purposes of any type of space-charge-flow devices (e.g., electron guns, ion guns for space propulsion, linear accelerators, etc.) and enable the engineer-designer to arrive quickly and cheaply at an optimum configuration.     

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.     

Evaluation of the DC parameters and noise transport in the gun region of an injected-beam crossed-field diode

A half-Maxwelliany-component velocity distribution and a full-Maxwellianz-component velocity distribution are assumed in order to evaluate the position and depth, ymand Vm, of the potential minimum as a boundary-value problem. The various dc parameters such as the voltage distribution, space-charge density, velocity and current density components and trajectories are then evaluated as an initial-value problem. The results obtained in this manner agree closely with the results obtained from the Kino gun model except that they-component current density is not constant, as is usually assumed in the Kino gun model. The steady-state parameters are calculated here for both temperature-limited and space-charge-llmited conditions. The Kino gun results are shown to be essentially those for space-charge-limited operation. Even though the injection conditions under the two types of operation are identical, the formation of a potential minimum considerably changes the electron trajectories and the corresponding velocity components. The growth rate of a hybrid wave is reduced as ωpis decreased and/oromega/omega_{c}is increased, and the propagation constants of the two conventional space-charge waves are modified, the over-all growth rate of the slow wave being greater than that of the fast wave. For large values of ωpthe conventional fast space-charge wave is a backward wave, although it becomes a forward wave ifomega/omega_{c}is large. It is noticed that the conditions in the gun region are more favorable to the existence of low-frequency perturbations. Based upon these results several experimental observations made at various laboratories are explained qualitatively.     

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.     

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.     

Digital computer analysis of axially symmetric electron guns

A digital computer program written in the IBM 7090 FORTRAN programming system is described and then employed in the analysis of several axially symmetric electron guns. The digital program employs relaxation techniques while alternately computing electric fields and trajectories. One cycle through the program consists of three parts. 1) Calculation of the voltages within the electron gun by solving Poisson's equation, in difference form, on a matrix containing a maximum of 10 000 points on which electrode potentials are laid out. 2) Calculations of new current densities along the cathode and the setting up of new trajectory starting points along the cathode to simulate these current densities. 3) Calculations of trajectories, including magnetic fields and relativistic effects if desired, and comparison of the new beam with the previous one. Thermal effects and direct particle-particle interaction effects are ignored although space-charge effects, introduced through the field calculations, tend to prevent excessive or usual trajectory crossings. Execution time for the entire program is between 4 and 12 minutes, although for most guns 5 to 7 minutes is usually sufficient. Results produced by the program are presented and compared with experimental and analytical results.     

Computer-aided design of electron guns for injected-beam crossed-field amplifiers

A two-dimensional self-consistent computer-aided CFA gun analysis program is discussed which can be used to solve for the characteristics of "long" crossed-field guns with arbitrary electrode shapes and including the effects of space charge. The results of analyzing a "long" Kino gun show excellent agreement between the theoretical gun parameters and those obtained by the computer analysis. The model shows promise of also being useful in the analysis of noise in CFA guns.     

层流枪用于电子束管的研究

着重研究层流枪在电流调制过程中特性参量的变化情况，并利用计算机计算结果优选方案，求得在常规调制过程中保持良好层流性的电子枪结构，根据设计装配了样管，实验结果与计算数据一致。     

A method of reducing the effects of anode aperture in high-perveance convergent electron guns

A new theoretical method of designing convergent electron guns of high perveance for use in microwave tubes is presented here. A differential equation which represents electron trajectories in a convergent electron stream has been deduced under certain approximations. Electron trajectories in an electron stream and boundary values along its boundary were numerically calculated by solving the differential equation by means of an electronic computer. Boundary values on the virtual anode surface under space-charge-limited conditions were used as the initial values for the calculations. Focusing electrodes were determined to satisfy the boundary conditions on the stream boundary. The design procedure is also shown. The electron guns designed by this method are somewhat different in structure from the conventional ones which are usually designed experimentally rather than theoretically. In these new electron guns, nearly uniform current densities will be obtained over the whole cathode area, while in conventional convergent guns of high perveance, electron emission density near the center of the cathodes is usually reduced due to the influence of the anode aperture. Laminar flow will be obtained at points near the minimum stream diameter also in guns designed by this method. Digital computer experiments were performed and the results proved this hypothesis to be reasonable. An electron gun of 1.72 × 10^-6perveance and area convergence ratio of 70:1 is shown as an example.     

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。     

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.     

Extremely Low Excess Noise in InAs Electron Avalanche Photodiodes

Measurements of the avalanche multiplication noise in InAs p-i-n and n-i-p diodes at room temperature demonstrate unambiguously that the avalanche multiplication process is dominated by impact ionization of electrons. This results in the excess noise factor for electron initiated multiplication asymptotically approaching a maximum value just less than two and becoming virtually gain-independent for higher gains. Measurements for predominantly hole initiated multiplication show corresponding high excess noise factors suggesting the electron to hole ionization coefficient ratios are comparable to those reported for $hbox{Hg}_{1-{x}}hbox{Cd}_{x}hbox{Te}$ electron avalanche photodiodes.      

Some experiments with a new type of crossed-field gun

The construction and testing of a crossed-field gun based on an exact space-charge flow solution will be described. All the characteristic parameters of a gun of this type may be obtained analytically. Experimentally the gun was found to perform essentially as predicted. This gun has a moderately high convergence and produces a beam whose gross features give a very good approximation to planar Brillouin flow. Work by Anderson has indicated that crossed-field beams produced by a gun of this type may be somewhat less noisy than similar beams produced by other types of guns.     

A low-frequency noise analysis using the two-dimensional numerical analysis method

A low-frequency (1/f) noise analysis is presented for a MOSFET. Poisson's equation and current continuity equation are numerically Solved to determine hole and electron concentrations in two dimensions, The Power spectrum of the fluctuation in the drain currentS_{i}_{d}is calculated by using obtained hole and electron concentrations, current distribution, and mobility distribution, based on the number fluctuation (NF) and mobility fluctuation (MF) models. It is found, from the comparison with experiments for n- and p-channel surface mode MOSFET's, that both NF and MF models can explain noise characteristics for surface-mode MOSFET's. In the case of a depletion-mode MOSFET, the MF model shows thatS_{i}_{d}is proportional to drain current id, which is in agreement with the experimental result for a commercial depletion-mode MOSFET. However, the NF model cannot explain theS_{i}_{d} alpha i_{d}characteristic.     

彩色CRT高分辨率电子枪技术

本文综合简介了日本三大类高分辨率电子枪技术,第一类是三角形电子枪;第二类是一字形电子枪,也是目前在彩色高分辨率 CRT 中广泛使用的电子枪,文中着重介绍其改进;第三类是单枪三束电子枪。最后,还简单介绍了高分率电子枪用阴极。     

Stability criterion for Gunn diodes with injection-limiting cathodes

According to McCumber [1] a Gunn diode with an ohmic cathode (i.e., "differential cathode conductivity"sigma_{c} = delta) is stable in a constant-voltage circuit ifn_{0}L le (n_{0}L)_{crit} equiv 2.7 times 10^{11}cm^-2wheren_{0}Lis the doping-length product. We show that the same stability criterion applies to Gunn diodes with an injection-limiting cathode(sigma_{c} rightarrow 0), if(n_{0}L)_{crit}is allowed to be a function ofsigma_{c}L. The value of(n_{0}L)_{crit}increases by 30 percent if(sigma_{c}L)varies from infinity (ohmic cathode) to zero (injection-limiting cathode). If a cathode with negative differential conductivity is realizable, it may be possible to extend the(n_{0}L)region of stable operation of Gunn diodes drastically.     

微电真空折叠波导行波管放大器的电子枪设计

研制工作于太赫兹波段的微电真空折叠波导行波管(FWG-TWT)放大器,需要设计束流集中且发射度小、结构紧凑的热阴极电子枪.本文首先依据典型皮尔斯电子枪的设计理论,通过编程计算初步选定了热阴极电子枪的基本结构参数,然后利用模拟工具对电子枪的结构参数模型进行了初步的仿真优化.针对工作频率为0.22 THz的微型折叠波导行波...     

Minimum noise figure for magnetron injection guns

A minimum noise figure has been derived for the magnetron injection gun. This theoretical expression is based upon RF equations which were developed to calculate the transport of current and velocity fluctuations along a planar 3-dimensional space-charge flow. Current and velocity fluctuations at the magnetron gun output were found to be correlated regardless of the assumed cathode conditions. The resultant minimum noise figure expression incorporating correlation is valid for any planar, lossless O-type device utilizing a magnetron injection gun. The variations of magnetron gun-velocity fluctuations, current fluctuations, and minimum noise figure versus transit angle and cathode-magnetic field angle were plotted assuming that the noise at the potential minimum consisted of the traditional values of uncorrelated shot current and mean-square velocity fluctuations. The noise figure for the other values of the dc magnetron-gun parameters and assumed cathode-noise conditions are easily calculated since all expressions are in closed mathematical form. Comparisons between this theoretical minimum noise figure and the noise performance of an operational multicavity klystron were made.     

Theory of cathode trajectory characterization by canonical mapping transformation

The paraxial lens theory cannot directly be applied to the cathode trajectories inside the gun. This inconvenience makes the interpretation of cathode trajectories difficult since one cannot use the physical concepts familiar in the paraxial lens theory, such as focal length and magnification factor. We have proposed the canonical mapping transformation (CMT) to describe the electron trajectories inside the gun by relating the ray conditions on the cathode surface to those in the crossover plane. The method takes as variables the distance along the surface and the sine of the ray angle with respect to the surface normal to define ray conditions. It has been shown that the CMT can be characterized by a small number of optical parameters. One of the parameters is the 'electron gun focal length', an extension of the image side focal length in the paraxial lens theory. The crossover size of a triode gun can be calculated from the electron gun focal length and the initial transverse energy spread. The calculation predicts the dependence of the crossover size on the grid voltage due to the change in the electron gun focal length. The prediction is compared with the measurement and shows good agreement with it. Since the CMT optical parameters can be calculated from the representative trajectories only and as they predict practically all the necessary source properties of guns, the CMT can be used as a practical tool in the designing of various types of electron guns.     

The.assessment of relative electron gun performance The assessment of relative electron gun performance Comments on the paper entitled “ Digital computer studies of electron guns for electron microscopes “†

A method of comparing the basic performance of electron guns is described. The method is applied to some recently computed results on two versions of an electron gun which has a hairpin-filament cathode.