系统电磁脉冲空间电荷层振荡特性理论

从电磁场理论出发,给出了发射电子为单能条件下系统电磁脉冲(SGEMP)空间电荷层振荡特性的解析求解方法,得到了空间电荷层的振荡频率和振荡幅度的解析式,其结果与用等离子体理论求解得到的结果一致。通过本文的研究工作,可以进一步认识发射电子为单能条件下SGEMP中的空间电荷层问题,该问题可以分别用电磁场理论和等离子体理论处理。     

用粒子模拟方法研究SG-III装置的腔体SGEMP

X射线照射金属腔体后,会在内部空间中发射出大量光电子,从而产生很强的系统电磁脉冲(SGEMP)。激光惯性约束聚变(ICF)装置内的X射线环境非常复杂,在靶室内工作的诊断设备即使有良好的电磁屏蔽,仍会面临严重的SGEMP干扰。以神光-III(SG-III)装置靶室内部的X射线环境为背景,采用时偏时域有限差分(FDTD)方法和粒子模拟(PIC)方法对二维圆柱腔体模型内部的SGEMP进行数值模拟。针对电磁场的振荡现象,在传统的粒子模拟算法基础上采用时偏方法进行滤波,去除了高频误差对计算的影响,结果更加准确。最后,得到的SG-III装置靶室内SGEMP干扰约为1.5 MV/m。     

大气层外弹道式目标红外辐射分布研究

论述了弹道式目标大气层外飞行过程中红外辐射分布的理论计算方法．并编制了相应的计算机程序。以某钝锥体外形弹道式目标为例，对夜间和午间条件下其发射和反射的红外辐射频谱分布和空间分布分别进行了数值计算。计算结果验证了理论方法和计算程序的正确性。     

X射线辐照下材料电子发射特性的模拟

稳态 X 射线管是一种重要的 X 射线辐照模拟装置,在辐照效应等研究领域有重要应用。采用蒙特卡罗模拟方法计算了 50 kV,150 kV 和 225 kV 管电压下的 X 射线能谱,并对 X 射线辐照下电子发射进行了模拟;研究了准直孔直径分别为 2 mm,4 mm 和 6 mm 条件下 X 射线的焦斑分布和电子发射弥散情况,以及不同能谱的 X 射线轰击到聚乙烯、聚酰亚胺、Si、SiO₂、Cu、Ta 和 W等样品上产生的电子发射能谱和电流强度等特性,为 X 射线辐照下材料电子发射特性的实验研究和设计提供一定的理论基础和指导。     

SGEMP等效脉冲电流注入波形研究

采用电磁范数对系统电磁脉冲(SGEMP)脉冲电流注入(PCI)波形参数的确定方法进行研究。负载分别为高阻和低阻时,对SGEMP敏感端口响应典型波形进行电磁范数参数化表征,综合考虑等效波形的上升时间、峰值、携带的能量和电荷量与响应波形的差异情况,开展了PCI等效波形参数研究。仿真结果表明,方波等效波形可以很好地模拟出响应波形,等效波形与响应波形的峰值一致,频谱特征近似;等效波形的上升时间、携带的能量和电荷量等参数通过调整脉宽即可实现与响应波形一致。因此,可采用电磁范数对SGEMP响应波形进行参数化表征等效,获得的等效波形容易在实验室生成,从而为采用电流注入方法开展SGEMP研究提供一种新的途径。     

线缆系统电磁脉冲实验中的抗干扰设计

为建立线缆系统电磁脉冲只有X射线的理想实验辐照环境,提出了一种针对同轴线缆的线缆系统电磁脉冲实验中的抗干扰设计。通过在实验同轴线缆外部套一层管状金属屏蔽,有效降低外界电磁辐射干扰,同时降低屏蔽本身发射电子对实验线缆产生的耦合,最终根据测到的信号反推出真实的系统电磁脉冲(SGEMP)响应。仿真计算与辐照实验验证了抗干扰设计的可行性。对实验线缆的仿真所得电压时域波形与实验结果基本一致,在误差范围内,可以认为仿真结果与实验结果基本吻合。     

波导传播特性的二次FEM方法分析研究

介绍二次有限元法分析波导本征值问题的基本原理和计算过程,编制相应的程序,实例计算了矩形波导的截止波长,并与理论值进行比较,所获得的计算结果与相关文献中所报道的数据吻合较好,表明该方法的有效性和程序的正确性。而且在此基础上计算了几种背脊波导的截止波长,单模带宽,画出了波导的场结构。这些结果和计算数据将为背脊矩形波导器件的小型化提供指导,对工程设计具有一定的实用价值。     

利用X_α—重叠球方法研究半导体的局域电子结构——Ⅱ.共价半导体金刚石和硅的轨道能级

本文利用X_α—重叠球和电荷分割方法计算了完整的共价半导体金刚石和硅的能谱.它们的禁带宽度(3a—3t_2)分别为5.2和2.0eV.价带宽度(3t_2—1a_1)分别为16.46和11.42eV.除了硅的禁带宽度数据偏大外,其他计算数据与实验和某些理论结果基本相符.文中还讨论了禁带内出现1t_1能级的原因以及与实验能谱的比较.     

场致发射显示器件专用模拟软件的设计

设计开发了场致发射显示器件专用模拟软件,该软件以MATLAB为平台,采用以有限元法为基础的FEMLAB软件对场致发射区域内的电场分布进行计算,自行编制了FED模拟软件从MATLAB中取出FEMLAB输出的数据,分析阴极表面场致电子发射状态,计算电子在空间的轨迹和在阳极的落点,将计算结果输出至MATLAB,以图形方式绘出电子轨迹和着屏光点.在计算电子轨迹时采用了动态内存分配方法和可变索引数据结构,提高了程序的通用性和移植性.该软件界面友好、使用方便,可对任意结构的FED进行计算,可在器件研制之前对FED的特性进行研究.     

ONETRAN计算结果与钴~(60)剂量分布数据比较确定光子能谱

用ONETRAN法则计算了金-铝界面附近在100keV至1250keV光子能量下的剂量分布。用从最小二乘方得到的4级光子能谱加权以测量剂量分布数据,计算出的剂量分布与在钴~(60)电离室里测量到的数据很接近。     

Comparison of FDTD particle pushing and direct differencing ofBoltzmann's equation for SGEMP problems

Now that personal computers (PCs) have become so powerful, the question has arisen as to whether particle-pushing or Boltzmann's equation codes are more efficient/accurate for solving self-consistent SGEMP problems on a PC. In this article, in the interest of achieving a code comparison, similar 2-D problems are treated using the two approaches on a PC. When enough modeling detail is included to cause the two codes to yield similar accuracy, it appears the particle-pushing code is about five times faster than the Boltzmann code. This result is probably qualitatively applicable to most SGEMP problems, except those where secondary-emission effects are important. When significant secondary emission occurs, particle pushers would lose at least half of their efficiency advantage. It is likely that the conclusions presented here do not carry-over to massively parallel computer architectures     

MAFIA在行波管多级降压收集极模拟中的应用

评述了传统二维稳态轨迹程序模拟多级降压收集极计算方法,同时提出了使用MAFIA 大信号分析软件对多级降压收集极进行全三维动态PIC模拟的方法和收集极效率简化计算公式。初步模拟实例表明该方法与实验结果吻合较好,为收集极的精确模拟和优化设计提供了新的途径。同时也指出了该方法存在的不足。     

能散度与发射度模块在太赫兹FWTWT模拟中的应用

研制了三维全电磁粒子模拟大规模并行程序 NEPTUNE3D 的能散度和发射度模块,主要用于评估电子出射速度和方向分布对太赫兹折叠波导行波管(FWTWT)性能的影响。将能散度和发射度模块应用到0.22 THz 的 FWTWT 器件粒子模拟中,结果表明：能散度主要通过改变器件束压范围,使其偏离束波互作用共振电压范围,导致器件性能下降;发射度反映电子发射角的发散,同时影响纵向与横向电子速度,电子横向速度的增加导致其更易碰撞通道内壁,使电子总数下降,导致器件性能下降;若束压保持不变,电子横向速度的增加势必导致轴向速度的减小,破坏束波同步条件,导致器件性能进一步下降。     

QWIP focal plane array theoretical model of 3-D imaging LADAR system

The aim of this research is to develop a model for the direct detection three-dimensional (3-D) imaging LADAR system using Quantum Well Infrared Photodetector (QWIP) Focal Plane Array (FPA). This model is employed to study how to add 3-D imaging capability to the existing conventional thermal imaging systems of the same basic form which is sensitive to 3–5 µm(mid-wavelength infrared, MWIR) or 8–12 µm (long-wavelength infrared, LWIR) spectral bands. The integrated signal photoelectrons in case of short integration time is required to transmit laser pulses with higher energy in order to obtain photoelectrons nearest those values obtained from the background photoelectrons in thermal imaging system with the longer interval of time. Since the operating conditions of the proposed system are of low levels for speckle diversity and high levels of signal photoelectrons, it was shown that the signal obeys the Gaussian probability density function. The evaluation of system performance of the proposed model shows that it needs a detector with low dark current and high transmitted energy to obtain satisfactory parameter values.     

Effect of geometric azimuthal asymmetries of PPM stack on electronbeam characteristics [TWTs]

A three-dimensional (3-D) beam optics model has been developed using the electromagnetic particle-in-cell (PIC) code MAFIA. The model includes an electron beam with initial transverse velocity distribution focused by a periodic permanent magnet (PPM) stack. All components of the model are simulated in three dimensions, allowing several azimuthally asymmetric traveling wave tube (TWT) characteristics to be investigated for the first time. These include C-magnets, shunts and magnet misalignment and their effects on electron beam behavior. The development of the model is presented and 3-D TWT electron beam characteristics are compared in the absence of and under the influence of the azimuthally asymmetric characteristics described     

Performance analysis of 2-D time-wavelength OCDMA systems with coherent light sources: code design considerations

The performance of two-dimensional (2-D) time-wavelength (TW) optical code-division multiple access systems at both physical and data link layers is considered in the presence of a multitude of noise sources. Particular consideration is given however to both beat noise (BN) and multiple-access-interference effects. A general procedure for calculating BN is presented. Comparisons between several 2-D TW codes comprising single-pulse-per-column/row and multiple-pulse-per-column/row strategies are performed. Results reveal that BN is strongly dependent on the code properties and the distribution of wavelengths within a code. Several aspects for 2-D TW code design are presented that mitigate the effect of BN.     

Three-dimensional simulation of multistage depressed collectors onmicro-computers

A three-dimensional (3-D) package for simulation of asymmetric and crossed-field multistage depressed collectors for microwave tubes has been developed. This package is based upon the 3-D finite-difference code KOBRA3-INP. The main features of the package are a user-friendly input interface, post-processors for collector analysis and calculation of secondary electron trajectories, and versatile output graphics. Both PC and mainframe versions of the package have been developed. The results of simple benchmark tests and those of simulation and analysis of asymmetric and crossed-field collectors including the effects of secondary electrons are presented. It is found that the asymmetric hyperbolic electric field collector shows very low backstreaming. It is shown that the representation of trajectories in energy space gives a better insight into the behavior of individual trajectories than plotting in coordinate space. The package will be useful for designing novel types of depressed collector     

Resonant coupling of near-infrared radiation to photonic bandstructure waveguides

Sharp resonance features are observed in the polarized reflectivity spectra of semiconductor photonic crystals fabricated by deep periodic patterning of AlGaAs surface waveguides. Both one- (1-D) and two-dimensional (2-D) lattices are studied by angular dependent reflectivity. By comparison with theory we show that the sharp features in reflectivity arise from resonant coupling of the external radiation to the folded band structure of the photonic crystal waveguides. Wavevector selective coupling to “heavy photon” states at the edge of the photonic Brillouin zone is demonstrated for the 1-D lattices. In the case of the 2-D lattices we observe polarization mixing of the photonic hands. Theoretical reflectivity spectra were obtained from a numerical solution of Maxwells equations for the patterned waveguide and were found to be in very good agreement with experiment