水中金属丝爆引燃铝粉悬浮液冲击波增强效应

开展了水中铜丝电爆炸引燃铝粉悬浮液的实验研究,将铝粉悬浮液置于有机玻璃管中,同轴心方向穿过200 μm的金属铜丝,经脉冲功率驱动后快速相变发生电爆炸为铝粉爆燃提供反应条件。通过比对不同质量球状铝粉（μm粒径）的悬浮液在相同脉冲电容器储能条件下的放电和冲击波参数,获得了电爆炸驱动铝粉放电特性和冲击波增强效应的规律。实验发现,电爆炸起爆铝粉的冲击波有两个明显的波峰,分别对应于金属丝电爆炸（一次冲击波）和由产物气体胀裂管壁产生的二次冲击波,且铝粉爆燃对二次冲击波的增强效应非常显著,在300 mg铝粉的悬浮液环境中,二次冲击波峰值达到2.77 MPa,是无铝粉添加环境中二次冲击波的2.25倍,冲击波冲量增强了约50%。对不同储能条件下200 mg铝粉的悬浮液环境中金属丝爆的冲击波进行了对比研究,发现随着驱动源储能的增加,电爆炸引发的主冲击波和二次冲击波压力均逐渐增大,600 J时分别达到了3.17和1.91 MPa,冲击波冲量也随储能增加而增加,在600 J储能条件时的冲量为41.12 Pa·s,储能条件约300 J时20.24 Pa·s冲量的2倍。     

辐射驱动下主动式高精度冲击波速度精密诊断技术

激光加载可以产生比气泡加载更高的压力,是高压状态方程研究中一种新的加载方式。在激光加载高压状态方程(EOS)研究中,台阶靶是常用的靶型。针对传统台阶靶存在的预热膨胀问题,提出了使用主动式任意反射面速度干涉仪(VISAR)进行台阶靶预热和冲击波测量的方法。该技术利用条纹图移动量计算厚度增加量,利用冲击波到达自由面产生条纹跳变的时刻来获得精确的冲击波到达时刻。通过修正已测量台阶厚度与膨胀量,可以获得更加精确的台阶厚度值。通过精确的时间间隔可以得到冲击波传输的时间。在匀速传输的条件下可以获得高精度的冲击波传输速度。该方法在辐射驱动超高压条件下具有很好的适用性,可以为状态方程实验提供高精度的冲击波速度数据。     

激光冲击强化“残余应力洞”的形成机制

利用ABAQUS有限元软件进行了单个圆形高斯光斑的激光冲击强化数值模拟,分析材料表面光斑中心区域形成的"残余应力洞"现象,并通过分析材料的动态力学响应特征揭示了"残余应力洞"的形成机制。结果表明:在冲击波加载时,光斑边界处会产生很强的剪切应力,形成向四周传播的表面稀疏波和向材料内部传播的剪切波。当稀疏波同时传播到光斑中心,发生相遇、汇聚,使材料产生急剧的上下位移过程,造成冲击波加载塑性变形后的二次塑性变形。二次塑性变形中形成了较大的剪切塑性应变,并降低了冲击波加载阶段产生的轴向和径向塑性应变,使残余压应力降低,从而形成"残余应力洞"。     

冲击作用下金属表面微喷射的分子动力学模拟

利用二维分子动力学程序,结合类紧束缚杂化多体势,研究冲击载荷下金属表面包含沟槽型缺陷的微喷射动力学过程.在产生微喷射以后,结果表明材料内部传播着两种波系:反射稀疏波和二次加载压缩波,其中,反射稀疏波波面与沟槽形状相似,而二次压缩波波面随沟槽夹角的变化而变化;并形成了两个压强区:负压区和正压区,负压区的存在表明材料中可能产生微损伤.同时,统计结果表明微喷射体的速度随沟槽半角增加而增加的趋势,微喷射体的粒子数随沟槽半角增大而减少的趋势,当沟槽半角大于60°,微喷射效应消失.以上计算结果可以定性说明射流是沟槽型 关键词： 冲击波 沟槽型缺陷 微喷射 分子动力学     

利用成像型速度干涉仪进行聚苯乙烯材料中冲击波调速的实验研究

利用一维实验,模拟了惯性约束聚变中烧蚀层中冲击波传输和多次冲击追赶过程.针对聚苯乙烯材料(CH)容易被X射线离化的问题,通过较详细的数值模拟,分析了用Au和Cu做阻挡层对冲击波信号的影响.利用两种不同的辐射源,研究了辐射源两个台阶强度变化对两次冲击信号的影响.经过分析,使用在Al基底上面加厚度为5 μm的Au膜以挡X射线的办法,获得了单次冲击在CH材料中加载和减速的清晰条纹图.利用在Al基底上加厚度为2 μm的Au膜和厚度为3 μm的Cu膜的方法,获得了两次冲击在CH材料中加速、减速和二次加载的条纹图.实 关键词： 光学诊断 冲击波调速 离化效应     

三介质Mie-Grüneisen混合模型在水下爆炸防护层问题中的应用

研究水下爆炸中的防护层问题，将爆炸气体、水、防护层或其他材料看成一个混合流场后，它们的物理状态可以直接用统一形式的Mie-Grüneisen状态方程来表示，再用Mie-Grüneisen混合模型模拟爆炸气体、水、固态防护层之间的复杂相互作用。计算时，通过状态方程中的特定参数来区分流体成分的物理特性，并通过体积分数来区分界面，同时添加自由进出口边界条件；计算过程中，对防护层的效果进行细致研究。研究发现，防护层的效果取决于材料的冲击阻抗。当冲击波从一种介质进入新介质时，在新介质冲击阻抗较小的情况下其压力会降低。同时，进入防护层的冲击波被结构物反射又会形成第二个冲击波。在这个过程中，对防护层的厚度和距离进行关注，但是这两个因素并未产生重要影响。     

气体炮技术

气体炮是当前世界上应用最广的实验室用冲击加载装置，由于气体炮具有高速发射弹丸的能力，它的冲击加载可在固体材料中产生几百ＭＰａ至几百ＧＰａ的冲击波压力，是研究材料在动态高压下的状态方程、本构关系以及断裂和相变的有效工具．同时，也是研究高速弹道学的理想装置。文章介绍了一、二级气体炮的一般工作原理和相关技术，讨论了其使用特点和当前水平，并简要介绍了几个典型的应用实例．     

爆轰加载下弹塑性固体Richtmyer-Meshkov流动的扰动增长规律

研究了冲击波加载弹塑性材料扰动自由面的动力学演化过程,分析了高能炸药爆轰驱动时初始扰动与材料性质对扰动增长的影响.研究结果表明:初始扰动的振幅与波长之比越高,扰动越易增长,强度越高的材料扰动增长幅度越小;扰动增长被抑制时,尖钉的最大振幅与增长速度无量纲数之间存在线性近似关系,进一步理论分析表明尖钉的振幅增长因子与加载压力、初始扰动形态和材料强度有关,该理论关系作为扰动增长规律的线性近似在一定范围内适用于多种金属材料.     

激光驱动薄膜产生等离子体射流的条件分析

 以聚乙烯薄膜材料为研究对象,从实验物态方程出发,对强激光驱动薄膜材料时影响激光在薄膜后表面形成等离子体射流的主要因素,包括激光强度、波长、脉宽、气库膜材料及厚度,进行了理论和数值分析。研究表明,到达薄膜后表面的冲击波强度足够高时,能够产生气态或等离子体射流,否则卸载过程仍然为凝聚态;对于聚乙烯材料,形成等离子体射流的基本条件是到达薄膜后表面的冲击波强度达到约80 GPa以上;采用短波长、较高功率密度、较长激光脉宽的激光驱动具有低汽化温度、低电离阈值的薄靶,更容易实现等离子体射流。     

“天光一号”驱动的聚苯乙烯高压状态方程测量

聚苯乙烯等CH材料的高压状态方程研究对于ICF聚变点火具有重要意义.本文基于"天光一号"长脉冲激光装置开展了聚苯乙烯高压状态方程研究,理论模拟了靶内的冲击动力学过程,采用侧向阴影成像技术实验测量了不同厚度的聚苯乙烯平面靶和飞片靶,获得了靶内的冲击波速度与粒子速度等状态方程参数.结果表明:长脉冲激光驱动下CH平面靶内经历了明显的准等熵加载过程,并逐渐演化为弱冲击加载.实验测量平面靶压力12 GPa,飞片撞击靶压力34 GPa,与模拟结果基本相符.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.