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.     

Computer Simulation of Axis-Encircling Beams Generated by an Electron Gun with a Permanent Magnet System

Results from computer aided design of a novel electron gun generating axis-encircling beams are presented and discussed. Numerical experiments were performed by the new version of the software package GUN-MIG named GUN-MIG/CUSP. It is based on a self-consistent relativistic model and is developed as a problem oriented tool for analysis of electron-optical systems with magnetron injection guns (MIG) and electron guns with field reversal (cusp guns), forming axis-encircling beams. As a result of the simulations an electron-optical design of a novel electron gun with permanent magnet system was accomplished. The gun is expected to form high quality beams with small velocity spread and beam ripple. Parameters of the generated beams are appropriate for a prospective weakly relativistic high harmonic large orbit gyrotron (LOG). The development of such device is in progress now at the Research Center for Development of Far-Infrared Region (FIR Center) at Fukui University.     

随机波束研究超宽带室内多径信道特性

从随机桥过程出发引入随机波束概念,使用随机波束研究超宽带（UWB）室内多径信道的传播特性.将UWB信号多径传播轨迹视作随机过程的样本,得到建模多径信道传播特性的随机波束.使用随机波束构建UWB信道的多径传播模型,并给出使用随机波束方法分析UWB室内多径信道特性的算法.使用该信道模型对实际传播环境进行仿真分析,并与其它建模UWB多径信道的方法进行了比较.仿真得到的UWB信道的功率延迟分布特性与实验测量的结果非常一致,证明此方法的有效性.     

Characteristics of large-area filamentary guns used for the E-beam stabilization of gas lasers

The development of high-energy electric-discharge lasers has created the requirement for high-voltage large-area uniform-current-density electron beams. This paper describes the characteristics for a class of filamentary electron guns of novel electrode configuration that satisfies these requirements. Expressions are derived for the gun potentials, electric fields, and space-charge-limited current densities. A comparison is made between theoretical and experimental results for a low-voltage model gun. The operating characteristics for large-area high-voltage guns are also discussed.     

直接输出高阶横模激光器的实验研究

从理论和实验上研究了从激光器直接输出高阶拉盖尔-高斯（LG）光束和高阶厄密-高斯（HG）光束。首先从理论上研究了高阶LG光束和高阶HG光束的光强分布特性,并进行数值仿真。在实验研究中,利用445 nm的蓝光半导体激光器端面泵浦Pr:YLF晶体,在一定的条件下,能从平凹腔直接输出640 nm波长高阶LG光束和高阶HG光束。实验结果表明:从激光腔内输出的高阶LG光束和高阶HG光束与理论仿真基本一致。文中所报道的获得高阶模的实验装置简单,对产生高阶光束及其应用具有较重要价值。     

Triode electron injection systems for hollow beams

Novel electron guns, in which a conical hollow electron beam is projected at a large angle to the axis into a coaxial deflection region, were tested. The guns have a triode structure so that the perveance can be varied easily. The strong deflection increases the effective perveance of the beam and makes the trajectories insensitive to current variations. In the form of a device with the gun at a large radius and projecting the beam inward, the electron paths are sensitive to scattering in the gun. The inverted gun, projecting the beam outward, is relatively free from this difficulty. The systems generally behave as expected, and should be quite useful for initiating variable-current hollow electron beams in various available focusing arrangements.     

Modelling and Simulation of Magnetron Infection Guns for Submillimeter Wave Gyrotrons

The software package GUN-MIG has been developed for computer simulation of beam formation in magnetron injection guns (MIG). It is based on a fully relativistic self-consistent physical model which takes into account the specific problems and requirements that are being encountered in the analysis and design of MIG for gyrotrons. Besides providing a general outline of the physical models and the program implementation of the code, several illustrative examples of the numerical experiments with real MIG for submillimeter wave gyrotrons are presented and discussed.     

Effect of a magnetic field on the structure of a high-current electron beam with a compensated charge

A mathematical model of a high-current electron beam with a compensated charge is developed. The effect of the 3D axially symmetric magnetic field induced by the beam current is taken into account. The model is based on the method of current tubes, which makes it possible to calculate electron trajectories in the presence of an external axially symmetric magnetic field. It is demonstrated that, in the presence of an external axially symmetric magnetic field, the beam rotates around its axis and the azimuthal current is induced. The shapes of electron trajectories are strongly affected by the magnetic field of the azimuthal current. The electron trajectories are calculated for various beam currents and external magnetic fields. It is shown that a significant nonlinearity leads to crossing of the trajectories of the initially laminar beam, sheath formation after passing the crossover, and collisionless thermalization of the beam. The boundary of the region inside which the beam can stably overcome the first crossover is determined.     

Synthesis of systems formation of converging sheet electron beams at partial magnetic shielding of the cathode

The synthesis method of electro-optical systems forming converging sheet electron beams at partial magnetic shielding of the cathode is developed. Equations of the inerior and exterior problems of the synthesis method and an equation for estimation of the deformation of the configuration of the sheet electron beam in the transit channel are obtained in the paraxial approximation. The proposed method is used to simulate electron guns forming converging sheet electron beams with the electrical parameters similar to the parameters of the uncompressed electron beam for terahertz radiation sources.     

Fabrication and field emission characteristics of a novel planar-gate electron source with patterned carbon nanotubes for backlight units

This paper describes the fabrication of backlight units(BLUs) for a liquid crystal display(LCD) based on a novel planar-gate electron source with patterned carbon nanotubes(CNTs) formed by electrophoretic deposition. The electric field distributions and electron trajectories of this triode structure are simulated according to Ansys software.The device structure is optimized by supporting numerical simulation.The field emission results show that the emission current depends strongly on the cathode-gate gap and the gate voltage.Direct observation of the luminous images on a phosphor screen reveals that the electron beams undergo a noticeable expansion along the lateral direction with increasing gate voltage,which is in good agreement with the simulation results.The luminous efficiency and luminance of the fabricated device reaches 49.1 lm/W and 5500 cd/m2,respectively.All results indicate that the novel planar-gate electron source with patterned CNTs may lead to practical applications for an electron source based on a flat lamp for BLUs in LCD.     

大回旋电子枪中的CUSP磁场研究

会切(CUSP)磁场是产生大回旋空心CUSP电子注的关键,该文分别对CUSP磁场中双曲正切模式和Moster-Molnar模型进行探讨,通过理论分析和数值模拟,建立适合于大回旋器件用CUSP磁场的物理模型;并对CUSP磁场设计中的影响因数进行探讨;同时探讨了CUSP磁场与大回旋空心CUSP电子枪的关系,结果表明:改变CUSP磁场的阴极区磁场的变化对设计低速度零散、低纹波、高速度比值α的轴向环绕大轨迹CUSP电子枪有较大的影响。     

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.     

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.     

A theory for coupling gridded gun design with PPM focussing

This paper presents theoretical and experimental methods for the design and optimization of gridded Pierce electron guns. The design of periodic permanent magnet (PPM) focussing systems to control the nonlaminar beams originating from such grided guns is discussed. Simplified relationships are developed which directly couple the, heretofore separate, gun and PPM focusing design problems.     

Use of the BFCPIC and BFCRAY codes to describe space charge limited emission in electron guns for gyrotrons

Numerical modelling of an electron gun in the space charge limited regime requires determining the current density distribution as well as the electric fields and electron trajectories. This is a rather complicated self-consistent problem, since the space charge influences the electric field, which in turn influences the electron trajectories. Previous simulations of magnetron electron guns using the BFCPIC and BFCRAY codes used a simple emission model (constant current density) that is approximately valid for thermionic emission. The code has been modified to include space charge limited emission. Several different ways of doing this are considered. One of the models considered uses Gauss’s law to force the electric field on the emitter to vanish; it was used in the original version of BFCPIC for the simulation of ion diodes. A second is based on the use of Child’s law (locally), which may be more appropriate for extension to fully electromagnetic particle-in-cell (PIC) codes. Calculations were performed with both models, and the results compared with each other and with experiments performed at FZK.     

Design of hollow and strip beam guns

This paper covers a study of strip and hollow beam guns. An automatic electron trajectory tracer has been used to study the properties of the slit-anode lens common to these types of guns. A thin beam approximation was made so that a flat-bottom electrolytic tank could be used. The results of this study have been incorporated into gun design charts. Eight hollow beam guns have been built and tested experimentally. The experimental data of these guns compare favorably with the data obtained from the anode-lens study. The limitation of thermal velocities on the maximum area compression of strip and hollow beam guns is discussed. The experimental results of a focusing scheme which uses a uniform magnetic field to focus a hollow beam down concentric drift tubes are discussed.     

Convective gas mixing in the airways of the human lung--comparison of laminar and turbulent dispersion

A mathematical model of gas transport in the airways of the human lung with numerical solution of the corresponding differential. equation is presented. The model takes into account, along with the summed cross section of. the Weibel lung model, both convection and longitudinal dispersion of helium and sulphur hexafluoride in air. Simulation was performed using two dispersion coefficients corresponding to laminar and disturbed flow. Moreover, since the dispersion coefficients are closely related to the velocity, five constant flow rates were used for each computation and each simulation. Comparison between the model responses to laminar and turbulent dispersion was made in order to determine which plays the preponderant role in gas transport in the human lung. In addition, agreement between the experimental time constant of CO2 elimination during high-frequency ventilation and the predicted mixing time constant was satisfactory. It is concluded that Taylor laminar dispersion cannot play a significant role in the human airways; however, it seems that convective gas mixing with disturbed dispersion-corresponding to a quasi-steady state?can account for most observed gas transport phenomena during spontaneous breathing and high-frequency ventilation.     

MIS隧道器件电流-电压特性的数值模拟

本文建立了MLS隧道器件的电流-电压特性的数值模拟程序,提出了一种新的计算方法:龙格-库塔数值积分与边界条件的预估-校正处理相结合的算法.利用建立的程序模拟计算了两种不同氧化层厚度的MIS隧道器件的电流-电压特性.对TiW/Si肖特基二极管,考虑了界面态的静态和动态影响,模拟特性和实验结果相比,令人满意的一致.     

侧窗头罩高速层流流场光学传输效应数值模拟

高速流场光学传输效应是影响红外成像末制导技术在高速导弹上应用的关键。研究了气动光学传输效应中层流流场光学传输分量的计算方法。应用光线追迹法和物理光学方法研究层流流场引起的像偏移和低程度的像模糊，结合典型状态下的流场数据，进行了高速层流流场光学传输效应的数学仿真，得到了仿真计算结果。采用实际计算出的流场数据，得出的计算结果与工程计算的结果相比较，证明所建立的气动光学高速流场光学传输效应理论模型基本正确，可以用来进行仿真计算。     

Si/SiGe/Si HBT频率特性的解析模型与模拟

用解析的方法模拟了T＝300K和77K时，fT和fmax与集电极电流密度Jc的关系，在大电流下考虑了异质结势垒效应的影响。模拟结果和用数值方法以及实验所得到的结果一致。同时，还建立了与之相应的Si／SiGeeb异质结和SiGe／Sibc异质结电容模型。