多级降压收集极CAD中的二次电子发射模型

多级降压收集极被广泛应用于提高微波放大器件效率.多级降压收集极中的二次电子发射对其效率有重要影响.该文探讨了真二次电子、弹性反射电子、非弹性反射电子3种二次电子发射模型,对发射率、发射角度以及能量分布情况进行了深入分析,并对考虑二次电子后的收集极模拟计算收敛条件进行了讨论.上述结果在多级降压收集极CAD软件中得到应用,定量分析了其对多级降压收集极效率的影响.     

一种空间行波管收集极入口能量分布测试方法及应用

收集极效率是空间行波管整管效率的重要组成部分，收集极入口能量分布对收集极的设计至关重要。在行波管设计中，直接通过互作用仿真计算获得的收集极入口能量分布往往与实际存在较大偏差。本文介绍了一种使用收集极电极加电势构造空间势垒测试收集极入口能量的方法，并通过此方法测试了某空间行波管收集极入口能量分布，通过调整激励功率等方法构造与测试入口能量分布接近的收集极入口电子注，并使用此入口电子注对收集极电子光学结构进行了优化，取得了较好效果。     

空间行波管多级降压收集极的设计和模拟

多级降压收集极被广泛地应用于空间行波管的设计中,本文介绍了一种四级降压收集极的设计和模拟方法。通过对某一空间行波管互作用后的废电子注信息进行分析,得到电子注在收集极的入口条件,并且根据电子注入口条件确定各电极的电位,用行波管模拟软件模拟废电子注在收集极内的发射情况,计算出收集极的效率,通过分析电子注粒子运行轨迹和能量分布,优化收集极边界条件和各电极电位设置,提高收集极效率,降低电子回流率。结果表明：利用此方法计算得到的收集极效率达到80%以上,该模拟分析方法对行波管收集极的研究设计具有参考价值。     

D波段行波管三级降压收集极的设计

效率是行波管(TWT)的重要技术指标,为提高某一0.22 THz折叠波导行波管的效率,需设计多级降压收集极。对注波互作用后的电子注信息进行分析,估算收集极效率最高时的电压设置。利用电磁仿真软件对三级降压收集极电极结构和电压设置进行仿真优化,得到效率大于87.5%,回流电流小于0.328 9 mA的轴对称三级降压收集极;在第二电极入口采用斜口结构进行仿真优化,得到回流电流小于0.075 mA的非轴对称三级降压收集极。结果表明,采用斜口结构可以有效降低0.22 THz行波管多级降压收集极的回流电流。     

多级降压收集极中次级电子的研究

效率与电子回流率是考核多级降压收集极的重要指标,而多级降压收集极中次级电子的存在对效率和电子回流率有重要影响.因此,对次级电子的研究有重要意义.本文探讨了次级电子发射的物理原型,并根据其编制了相应的CAD程序, 在对多级降压收集极的试算中,取得了较好的效果.     

用于倍频程带宽、高性能行波管的小型、81～83.5％效率的2级和4级降压收集极

在美国空军(USAF)——国家航宇局(NASA)共同制定的规划中,Lewis研究中心正在进行电子对抗行波管效率的改进工作,它是通过采用多级降压收集极(MDC)以及在该中心所探索的对耗能电子注的再聚焦技术来实现的。在本规划的分析阶段,计算了整个行波管的三维电子注轨迹。轨迹计算一直到耗能电子注的再聚焦区和降压收集极。对收集极效率、收集极损耗和管子总效率进行了验证和计算。在实验工作方面,首先对不用多级降压收集极的管子性能进行估测,然后对耗能电子注的对称性、圆度和速度离散作了分析。最后,装上了多级降压收集极,使其性能最佳并进行了估测。对于理想的行波管,三维理论表明:具有对称、圆型并有最佳再聚焦电子注的2级多极降压收集极在中心频带有81％的效率(多级降压收集极),而4级多级降压收集极有85％的效率。实验结果所获得的数据表明:一个倍频程带宽——(4.8～9.6)千兆赫、功率为330～550瓦行波管的2级和4级降压收集极的最小多级降压收集极效率分别为81％和83％。     

行波管多级降压收集极的计算和实验研究

采用多级降压收集极是提高行波管效率析有效途径之一。本文在ＳＬＡＣ－２６６程序的基础上对一支带有二级降压收集极的国外行波管进行了计算，并且将计算结果同实验结果进行了比较。同时用电子注分析仪对降压收集极区电子注和纵向速度分布进行了实验研究，获得了该二级降压收集极的部分工作曲线，并对实验结果进行了分析讨论。     

多注行波管收集极的设计与模拟

多级降压收集极是提高行波管效率的有效途径,本文在粒子算法的基础上,编写了多注行波管收集极的专用软件,实现了电子收集的三维模拟,计算结果与二维程序进行了比较,并利用该软件设计模拟了一个五注行波管两级降压收集极,对计算结果进行了分析。     

多级降压收集极的模拟仿真软件

研制了一个微波管多级降压收集极的二维模拟计算软件MSDC。MSDC软件采用圆柱坐标系，计算静电场分布、注入的原电子的运动轨迹、原电子撞击电极引发的次级电子的发射和运动轨迹、电子运动形成的空间电荷密度等，最后给出多级压收集极的性能。本软件还具备再聚焦区电子注层流性计算功能，以便指导再聚焦区磁场分布的优化。本软件的主要特点，是考虑了次级电子的空间电荷效应，每次迭代计算、原电子轨迹和次级电子轨迹的影响全都包括进去。     

耦合腔行波管电参量对降压收集极特性的影响

该文基于Orprogr软件,在X波段模拟设计出耦合腔行波管的期待电性能,并利用互作用后的电子注为入口条件,优化设计出收集效率大于71.5%、电子注着陆相对均匀的三级降压收集极。在上述条件下,讨论了电子进入收集极层流性(速度比)、电极形状、电极电压以及收集极内电场分布对电子运动的影响,从物理上给出了电子注在收集极表面着陆特点的详细分析。     

多级降压收集极效率的优化

围绕着MDC的核心即提高效率问题,分析了MDC的物理模型,阐明了MDC的功率分布图并解释了其来源.利用MDC的入口条件生成的功率分布图,可以快速得到给定降压级数的MDC的最优化效率,以及各电极的最优化电位.在最优化电位附近进行模拟仿真,减小电位选择的盲目性,起到事半功倍的效果.     

Small-size 81- to 83.5-percent efficient 2- and 4-stage depressed collectors for octave-bandwidth high-performance TWT's

In a joint USAF-NASA Program, Lewis Research Center is carrying out an efficiency improvement program on traveling wave tubes (TWT) for use in electronic counter measures (ECM) by applying multistage depressed collector (MDC) and spent beam refocusing techniques developed at Lewis. In the analytic part of the effort, three-dimensional electron trajectories are computed throughout the TWT. Trajectory computation continues through the spent beam refocuser and the depressed collector. Collector efficiency, collector losses, and overall efficiency are identified and computed. On the experimental side, tube performance is evaluated first without the MDC; then, the spent beam is analyzed for symmetry, circularity, and velocity spread. Finally, the MDC is attached and its performance optimized and evaluated. The three-dimensional theory, for ideal tubes, predicts a MDC-efficiency, at mid-band, of 81 percent for a 2-stage MDC with symmetric, circular, and optimally refocused beams and 85.5 percent for a 4-stage MDC. Experimental results to date have yielded MDC efficiencies of a minimum of 81 and 83 percent for a 2- and 4-stage MDC, respectively, across a one-octave bandwidth of a 4.8 to 9.6 GHz 330-to-550-W TWT.     

Approximate formulas for crossed-field potential-minimum parameters

A parabolic potential distribution is assumed in order to study the static properties of the crossed-field potential minimum. The half-Maxwellian normal velocity distribution function and the full-Maxwellian transverse velocity distribution function are integrated over the initial velocity plane with the proper boundary conditions to find an expression for the ratio of beam current to emission current. For conditions satisfying most practical cases, this current-sorting expression is reduced to a very simple form. Using the current-sorting equation together with the expression which relates the potential minimum position to the minimum potential for zero magnetic field, an approximate method of determining the potential-minimum parameters is devised. The values obtained in this manner agree closely with the results obtained by other more exact (and more complicated) numerical methods.     

The use of miniature supersonic nozzles for microparticle acceleration: a numerical study

By means of a high-speed gas flow generated by a miniature supersonic nozzle, we proposed a unique biolistic method to accelerate microparticle formulation of drugs to sufficient momentum, to penetrate the outer layer of human skin or mucosal tissue for the treatment of a range of diseases. One of the main concerns for designing and evaluating this system is ensuring microparticles delivery into human skin with a controllable velocity range and spatial distribution. The initial experimental work suggested that the performance of the transdermal delivery strongly depends on aerodynamics of the supersonic nozzles employed. In this paper, computational fluid dynamics (CFD) is utilized to characterize existing prototype biolistic delivery systems, the device with a converging-diverging supersonic nozzle (CDSN) and the device based on the contoured-shock-tube (CST) design, with the aim at investigating the transient gas and particle dynamics in the supersonic nozzles. Whenever possible, predicted pressure and Mach number histories, 2-D flow structures, and particle velocity distributions are made to compare with the corresponding experimental measurements to validate the implemented numerical approach. The gas-particle interaction and performance of two biolistic devices are interrogated and distinguished. Subsequently, the particle impact conditions are presented and discussed. It is demonstrated that the CST can deliver microparticles with a narrow and more controllable velocity range and spatial distribution.     

TMS320C6X为核心的实时视频图像处理器的初步设计

探讨了TMS320C6X实时视频数字图像处理器的总体结构、各个部分的构成、功能以及所选用的主要器件,阐述了该设计方案的主要特点。最后指出了视频图像处理器关键器件的一些新进展。     

Monte Carlo simulation of GaAs Schottky barrier behaviour

The transport of carriers through the space-charge region (SCR) of a GaAs Schottky barrier is studied by the Monte Carlo simulation technique. Simulation results indicate that the carrier distribution is significantly perturbed from a Max-wellian near the metal-semiconductor boundary, limiting the validity of the commonly used thermionic diffusion model. Phenomena related to the disturbed distribution include increased recombination velocity at the interface and reduced carrier concentration near the junction. The interface recombination velocity is found to be constant with applied bias and the Bethe condition is shown to be more than sufficient to ensure the validity of the thermionic emission model.