自适应光学系统的数值模拟：动态控制过程和频率响应特性

对自适应光学系统的动态控制过程进行了数值模拟。与自动控制理论的解析分析相比,动态控制过程的数值模拟有其优越性。系统的频率响应特性与动态控制性能密切相关,对自适应光学系统的频率响应特性也进行了数值模拟。模拟计算的结果与实验测量结果符合得很好。还实现了多频率成份的同时计算,可以大大提高计算效率。其结果与单频率结果只在低频下有小的差别,可以满足得到带宽和裕量等参数的实用要求。将频率响应特性的模拟计算与长时间曝光斯特列耳（Strehl)比的数值模拟结合,可得到对自适应光学系统性能的有效评估。     

一种改善直耦增强数码相机静态成像时间响应特性的方法

理论上分析了CIDC1816型直耦增强数码相机在采集静态图像过程中像增强器阴极电压衰减时间对电子光学系统横向位移的影响.实验证明了阴极电压衰减时间会对荧光屏亮度衰减时间产生影响.提出了利用电子开关的高速响应特性来减小阴极电压衰减时间,以改善该类型相机时间响应特性的方法.研究表明,当外界光照条件大于10-4 lx时,阴极电压衰减时间由80~130ms减小到50~60ns,电子光学系统的横向位移受阴极电压衰减特性的影响减小,荧光屏亮度衰减时间由12~26ms减小到了3~4ms.研究结果证明了该方法能够有效地减小像增强器阴极电压衰减时间和荧光屏亮度衰减时间,为提高该类型相机静态成像质量提供参考.     

双阳极霍尔推力器效率及推力的模拟研究

为确定双阳极霍尔推力器中阳极电压分布对推力器效率及推力的影响，采用PIC三维数值模拟对双阳极结构霍尔推力器的放电过程进行了模拟。基于垂直分布的双阳极结构，得到了放电后离子羽流分布以及电子在放电区域的分布。通过对放电状态的模拟，计算得到了不同工况下的推力以及效率。在双阳极结构中第二阳极的电压增加会增大离子能量，但将影响电子约束，而过高的电压将引起电子密度减小。推力随着霍尔电流的增大而增大，但效率会随之减小，导致在提升推力的同时损失效率。     

轴对称静场系统聚焦特性

 建立了不等径双圆筒电极结构的旋转轴对称静电场电子光学聚焦系统模型,利用ANSYS软件,数值模拟了电子束在其内部场中的运动情况,给出了理论计算的像面和最佳成像位置。研究了电极形状、尺寸和负载电压等因素对系统成像特性的影响。得出了各电极负载对聚焦点位置影响的量化关系。研究表明：聚焦极对系统成像的影响比加速极和阳极大;聚焦极负载电压对成像特性的影响比电极尺寸和形状大得多。     

照明光学系统照度分布的计算机模拟分析

本文阐述了照明光学系统与传统成像光学系统的区别，提出了几种计算照明光学系统照度分布的原理和方法，并给出了一个具体的利用计算机对投影照明光学系统照度分布的模拟分析方法和运算结果。     

基于双波前传感器自适应光学技术的太阳光栅光谱仪

为了研究不同太阳大气高度的热力学特性,具有良好成像质量的成像型光栅光谱仪是实现这个目标的重要仪器。然而作为地基式太阳望远镜重要的终端仪器之一,光栅光谱仪的光谱成像性能不可避免的会受到动态波前像差和系统静态像差的影响。动态波前像差常通过在太阳望远镜系统中集成自适应光学系统进行补偿。针对光学系统中的由装调和光学元件加工等引起的静态波前像差,提出了一种基于自适应光学技术校正光栅光谱仪中静态波前像差的方法,并进行了数值模拟仿真和实验验证。实验结果表明,校正后系统的残余波前像差RMS≈0.025λ,此时波前像差对光谱分辨率和能量利用率的影响可忽略,提高了光栅光谱仪的光谱成像质量,证明了所提出的方法的有效性。此外它具有降低光学系统装调精度和光学元件加工精度要求的优点。     

采用多狭缝条纹管实现激光三维成像

为了实现高清晰,高准确的近距离和中距离探测,介绍了一种采用多狭缝条纹管实现激光三维成像的方法.多狭缝条纹管作为成像系统的核心器件,对成像准确起主要影响.通过对成像原理的分析以及条纹管参数之间的关系推导,对多狭缝条纹管的技术指标进行了计算和设计,得出了电子光学系统的主要设计指标.     

光学元件微缺陷处电磁场分布特性的数值计算方法

 神光Ⅲ的光学系统具有高功率密度运行的特点，对光学元件的抗激光损伤能力等提出了很严格的要求。光学元件内部的微缺陷会引起局域场强增强，采用时域有限差分方法对亚波长量级的缺陷进行了电磁场的数值模拟，并对数值计算的参数选取给出了定量的判断。     

电推力器流动模拟中的电子处理方法

 分析了电子的准中性假设、玻耳兹曼分布假设、粒子模型在电推力器流动模拟中的适用性和优劣性,提出了一种新的电子处理方法——电子漂移扩散近似,采用该方法模拟了离子发动机栅极光学系统等离子体运动过程。结果表明:该方法得出的电势分布、离子相空间分布及电子数密度分布与经典的电子玻耳兹曼分布假设处理方法计算结果一致,验证了该方法可以很好地应用于电推力器栅极光学系统模拟。     

一种高性能太阳敏感器复合光学系统设计

以夫朗禾费衍射理论为基础,结合微透镜,设计了一种高性能的数字式太阳敏感器复合光学系统。分析了光学系统的组成,建立了光学系统的数学模型,设计了光学系统的焦距、孔径和微透镜参量,并进行了成像的数值仿真。仿真结果表明,与基于掩模的光学系统相比,这种新型的复合光学系统成像光斑能量分布集中,保证计算光斑中心位置的高精度,使敏感器具有大视场和高精度的特点。     

轨道式多间隙气体开关设计与性能测试

针对直线脉冲变压器对低电感、低抖动气体开关的研制需要,采用垂直布放的平板轨道电极,组成具有通视结构的水平间隙,设计了一种多间隙轨道式气体开关。利用Meek击穿判据计算了单间隙自击穿电压,实测了4个单间隙的自击穿电压及其相对标准偏差,并根据单间隙自击穿电压,利用概率分析方法预测了多间隙开关自击穿电压,计算值与实测结果一致。研究表明:开关电感最大约109 nH,自击穿电压相对标准偏差为1.5%,在60 kV触发电压和48%~74%欠压比下,开关抖动0.9~2.6 ns。与圆环形电极的多间隙气体开关相比,多间隙轨道式气体开关自击穿电压更稳定,也更容易触发。     

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为了保障EAST快控电源系统的稳定运行,提出了一种适用于EAST快控电源的高频高压工作环境的交流绝缘监测技术.此方法利用电阻不平衡桥,通过交替投切电阻造成分压的变化,实时采集电压,计算出绝缘电阻值.搭建了Simulink仿真平台,分别将~220V市电和EAST快控电源输出作为电压输入进行实时绝缘监测仿真分析,波形与预期相符.经过实验验证,新方法能够准确完成220V市电交流输入的绝缘监测,并且在快控电源现场能正常工作,达到绝缘监测的精度要求.     

Ultrasonic transducers using electron-irradiated vinylidene fluoride-trifluoroethylene copolymers

Single-element, planar transducers have been fabricated using electron-irradiated poly(vinylidene fluoride-trifluoroethylene) 80/20 mol% copolymers with different electron dosage. Electrical field-induced strain response of copolymer film with 100 Mrad dosage has been studied at 5 kHz and the electrostrictive coefficient was calculated. The transmitting response of the air-backing and epoxy-backing transducers was evaluated with the application of high DC bias voltages. Clear ultrasonic amplitudes and high frequency spectrum (>20 MHz) were observed when driven from a standard ultrasonic voltage source through a decoupling circuit. It has also showed that larger generation of ultrasonic waves will be induced under high DC bias field, which is due to the increase of induced d(33) piezoelectric coefficient. Two different polar bias voltages, positive and negative, were applied to the transducers and inverse waveforms were received, which was coincident with the theoretical analysis of the strain response of electrostrictive film.     

适用于EAST快控电源的交流绝缘监测技术

为了保障EAST快控电源系统的稳定运行,提出了一种适用于EAST快控电源的高频高压工作环境的交流绝缘监测技术。此方法利用电阻不平衡桥,通过交替投切电阻造成分压的变化,实时采集电压,计算出绝缘电阻值。搭建了Simulink仿真平台,分别将~220V市电和EAST快控电源输出作为电压输入进行实时绝缘监测仿真分析,波形与预期相符。经过实验验证,新方法能够准确完成220V市电交流输入的绝缘监测,并且在快控电源现场能正常工作,达到绝缘监测的精度要求。     

Electro-optic characterization of tetragonal (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals by a modified Sénarmont setup

The refractive indices of tetragonal (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-xPT) single crystals were measured with a prism coupler and their linear electro-optic (EO) properties were investigated from 20 to 80 °C by the automated scanning Sénarmont system with an ac field. The composition and temperature effect on the EO coefficients were also discussed. It has been found that their EO coefficients are much larger than that of widely used LiNbO₃ single crystal and the calculated half-wave voltages are also much lower, which enable the operation at lower voltages and the smaller device dimensions. Since the excellent EO properties are very stable and such high quality single crystals with large-size have been obtained, the PMN-xPT single crystals are a very promising candidate for EO modulation applications. By linking to the polarization-related quadratic EO coefficients, we find that the linear EO properties are related with the spontaneous polarization and dielectric constants.     

基于统计学模型的真空绝缘堆闪络概率计算分析

对比了几种不同类型的过电压因子下绝缘堆闪络概率的特点, 考虑了多层均压及圆周渡越时间后得到的闪络概率更能反映绝缘堆耐压水平;简化计算统计学经验公式中矩阵可保持绝缘堆闪络概率计算值准确性并减少过电压因子的静电场计算次数。分析在固定间隙距离下绝缘环个数与电压峰值及电场强度峰值的关系, 计算结果表明:存在最优绝缘环个数承受最高电压峰值与电场强度, 承受最大工作场强的绝缘环个数下, 工作电压幅值已降低很多。在选择绝缘环个数时应综合考虑, 该计算方法可应用于工程绝缘结构设计中合理选取绝缘环个数。     

Effect of an electric field on the orientation of a liquid crystal in a cell with a nonuniform director distribution

The electric field-induced reorientation of a nematic liquid crystal in cells with a planar helicoidal or a homeoplanar structure of a director field is studied theoretically and experimentally. The dependences of the capacitances of these systems on the voltage in an applied electric field below and above the Fréedericksz threshold are experimentally obtained and numerically calculated. The calculations use the director distribution in volume that is obtained by direct minimization of free energy at various voltages. The inhomogeneity of the electric field inside a cell is taken into account. The calculation results are shown to agree with the experimental data.     

The Design of Megawatt Gyrotrons

The design parameters of a 120-GHz gyromonotron capable of output powers in excess of 1 MW are determined. A nonlinear model of the interaction between the beam and RF field is used in which the efficiency is a function of only three normalized variables. By expressing the technological constraints in terms of these variables, permissible design parameters yielding high-efficiency operation can be calculated. Constraints that are considered include ohmic heating of the walls, voltage depression of the beam, reduced coupling between the beam and RF field due to beam thickness, and efficiency degradation due to space-charge forces within the beam. An analysis of the trade-offs between current and voltage at the 1-MW level indicates that lower-order modes can be utilized at lower voltages, but the constraints based on current limitations are difficult to satisfy. An 80-kV 29-A design is presented that achieves a total efficiency of 44 percent. The primary uncertainty of these designs is the severity of competition due to parasitic modes. However, a number of isolated asymmetric modes appear capable of single-mode emission at 1 MW based on present experimental results. Multimegawatt operation is also considered. It is shown that powers exceeding 20 MW are possible if single-mode operation can be achieved in very-high-order modes. The methodology presented in this paper is general and can be easily adapted to other frequencies and output powers.     

Multiphysics modelling of the separation of suspended particles via frequency ramping of ultrasonic standing waves

A model was developed to determine the local changes of concentration of particles and the formations of bands induced by a standing acoustic wave field subjected to a sawtooth frequency ramping pattern. The mass transport equation was modified to incorporate the effect of acoustic forces on the concentration of particles. This was achieved by balancing the forces acting on particles. The frequency ramping was implemented as a parametric sweep for the time harmonic frequency response in time steps of 0.1 s. The physics phenomena of piezoelectricity, acoustic fields and diffusion of particles were coupled and solved in COMSOL Multiphysics? (COMSOL AB, Stockholm, Sweden) following a three step approach. The first step solves the governing partial differential equations describing the acoustic field by assuming that the pressure field achieves a pseudo steady state. In the second step, the acoustic radiation force is calculated from the pressure field. The final step allows calculating the locally changing concentration of particles as a function of time by solving the modified equation of particle transport. The diffusivity was calculated as function of concentration following the Garg and Ruthven [1] equation which describes the steep increase of diffusivity when the concentration approaches saturation. However, it was found that this steep increase creates numerical instabilities at high voltages (in the piezoelectricity equations) and high initial particle concentration. The model was simplified to a pseudo one-dimensional case due to computation power limitations. The predicted particle distribution calculated with the model is in good agreement with the experimental data as it follows accurately the movement of the bands in the centre of the chamber.     

随机耦合模型在高功率微波效应中的应用

分析了微波混沌腔体系统中关键部位感应电压的统计问题,介绍了随机耦合模型在高功率微波效应研究中的计算方法和应用,并以计算机机箱为实验系统,开展了电磁波耦合入计算机机箱腔体的电磁干扰问题研究,对其电路板上关键部位感应电压的统计计算和实验结果进行了比较,其结果基本一致。随机耦合模型在波混沌系统中感应电压的统计探讨为高功率微波效应、电磁兼容等研究提供了一种新的思路。