Upgrading of the RS-20E High-Current Accelerator for the Investigation of Shock-Wave Processes under Isochoric Energy Absorption

The scheme and parameters of the upgraded RS-20E electron beam generator on the basis of a plasma opening switch (POS) are presented. The output unit of the POS is modified to allow the use of optical diagnostics in investigating wave processes generated in transparent targets by the electron beam of the accelerator. A new optical diagnostic system is also presented. Its scheme allows the four-frame electron-optical registration of a sample in both its own glow and in the laser shadow during propagation of the shock wave generated by the electron beam.     

12MeV强流脉冲电子束对钽靶的破坏研究

强流高能电子束由于具有很强穿透能力,在材料内的能量沉积具有体分布特点,因此其对材料的辐照破坏体现出和低能电子以及X光等不同的特点.本文分析了金相显微镜和扫描电镜下的被12MeV的强流电子束轰击后的1.2mm厚度钽靶的破坏点形貌,其破坏断面体现为力学韧性撕裂,且关于靶中心基本对称.为了解释这种现象,文中用蒙特卡罗的数值模拟方法给出了电子束在钽靶内的沉积能量分布:能量沉积呈现靶中心吸能高,两侧低,且关于中心基本对称的特点.针对破坏断面特点和靶的吸热情况,我们给出高能电子束对靶材破坏初步的定性解释:认为高能电子束的强穿透能力使得靶材各部分几乎同时加热.靶材在极短时间里吸收大量能量,发生剧烈膨胀.由于能量沉积特点,中心部分材料膨胀最厉害,受到两侧边界的强烈约束,将产生两大小相近的热激波相对传播.激波在两侧自由界面反射,产生向内传播稀疏波.当两个稀疏波在靶中心区域相遇,就造成了靶对称撕裂的破坏形态.     

Measurements of the refractive index of polymethylmethacrylate behind the front of a shock wave excited by a high-current electron beam

The variation of the refractive index in polymethylmethacrylate (PMMA) behind the front of a shock wave excited by a high-current electron beam is investigated. The values of refractive index in a pressure range of 2 and 4 GPa are determined from the deviation of the diagnostic laser beam. The results are compared with the available data for shock compression of PMMA.     

“闪光二号”电子束辐照平板靶产生热击波的实验研究

 热击波是电子束辐照靶材料时在其内产生材料响应的一个重要力学现象。论述了近两年来我们在“闪光二号”装置上进行电子束辐照平板靶产生热击波的实验研究。使用的靶厚为2.8~6.5 nm,靶材为LY-12铝,靶上能通量为87~152 J/cm²。实验结果表明,实测热击波应力峰值为0.35~2.0 GPa,热击波平均作用时间约为0.29 μs,均半高宽约为0.14 μs,平均上升时间约为0.10 μs。     

Analysis of the Evolution of a Supersonically Expanding Plasma

A supersonically expanding arc plasma in argon is analyzed both experimentally and theoretically. The plasma is created in a cascaded arc and extracted through a hole in the anode. It emanates in a large vacuum system, where it expands supersonically. This expansion is limited by a shock wave. After the shock wave a subsonic plasma beam is created. A quasi one-dimensional model, based on the conservation of mass, momentum and energy is presented. The shock wave is treated as a discontinuity. The electron density, the gas velocity and the gas temperature are measured as a function of the position in the expansion by means of Stark broadening and Doppler spectroscopy. The model calculations agree well with the measurements, especially in the first part of the supersonic flow.     

聚酯材料在脉冲电子束辐照下的动力学效应与材料参数

对聚酯材料在电子束辐照下的动力学效应进行了研究。采用Monte Carlo方法,计算了脉冲电子束在聚酯材料中的能量沉积;采用流体动力学方法,对聚酯材料在电子束辐照下的热击波和喷射冲量进行了数值模拟;采用将喷射冲量和热击波压力的数值结果与实验测量结果进行逼近的方法,得到了聚酯材料的升华能约为1.1 kJ/g,Grüneisen系数的常态值约为0.2。     

On shock initiation in brisant explosives by a high-current electron beam

The feasibility of shock initiation in thin pentaerythritol tetranitrate (PETN) single crystals under the action of a pulsed high-current electron beam (0.25 MeV, 20 ns, 15 J/cm²) is shown experimentally. The real-time dynamic characteristics of crystal glow arising under the action of the electron beam and glow due to subsequent shock-wave-induced transformations are presented. A shock wave results from beam energy absorption and initiation of an exothermal chemical reaction in the irradiated layer.     

脉冲辐照热激波与压缩应力波

 扼要地阐述了X射线、电子束辐照材料时所产生的热激波与高速碰撞、炸药爆炸所产生的压缩波之间一些不同的现象特征，可为热激波的分析、研究以及模拟提供参考。     

多孔脆性材料对高能量密度脉冲的吸收和抵抗能力

作用在脆性结构材料表面的高能量密度脉冲会以冲击波的形式传播进入材料内部, 导致压缩破坏和功能失效. 通过设计并引入微孔洞, 显著增强了脆性材料冲击下的塑性变形能力, 从而使脆性结构材料可以有效地吸收耗散冲击波能量, 并抑制冲击诱导裂纹的扩展贯通. 建立格点-弹簧模型并用于模拟研究致密和多孔脆性材料在高能量密度脉冲加载下的冲击塑性机理、能量吸收耗散过程和裂纹扩展过程. 冲击波压缩下孔洞塌缩, 导致体积收缩变形和滑移以及转动变形, 使得多孔脆性材料表现出显著的冲击塑性. 对致密样品、气孔率5%和10%的多孔样品吸能能力的计算表明, 多孔脆性材料吸收耗散高能量密度脉冲的能力远优于致密脆性材料. 在短脉冲加载下, 相较于遭受整体破坏的致密脆性材料, 多孔脆性材料以增加局部区域的损伤程度为代价, 阻止了严重的冲击破坏扩展贯通整个样品, 避免了材料的整体功能失效.     

Direct evidence for thermal mechanism of plasma influence on shock wave propagation

Shock wave propagation through a glow discharge is studied by a double beam laser Schlieren method. A pulsed discharge is used to separate electron and other plasma related phenomena from thermal effects. The results prove the pure thermal nature of the influence of a plasma on a shock wave.     

Observation of the decay instability of a beam plasma wave

The spontaneous decay of a beam plasma wave into an ion acoustic and an electron plasma wave has been observed during the interaction of a monoenergetic electron beam with a helium and a neon plasma.     

电子束在材料中的能量沉积和热激波特性

采用解析法、矩方法和Monte Carlo法等方法,计算了电子束在硬铝靶材中的能量沉积.计算表明,3个结果基本符合.根据得出的能量沉积结果和一维应变弹塑性流体动力学模型,计算了电子束热激波在硬铝靶材中的传播,并将其应力峰值的计算值与实测值进行了比较.     

Laboratory modeling of the interaction of electron beams with a magnetoplasma

We present the results of laboratory experiments in which the mechanisms of interaction of electron beams with whistler waves in a magnetoplasma are studied. Different mechanisms of whistler generation during the injection of a modulated electron beam in the plasma are studied, and the mechanism of conversion of the beam kinetic energy to radiation is demonstrated. The processes of whistler wave generation by the modulated beam at the ˇ Cerenkov and Doppler resonances are analyzed in detail. The excitation of whistler waves by means of a nonresonant mechanism of the transition radiation is studied.     

Investigation of magnetohydrodymamic interaction in a supersonic air flow at <Emphasis Type="Italic">M</Emphasis> = 8

The influence of magnetohydrodynamic interaction localized before a model on the position of a shock wave attached to a wedge is experimentally and numerically investigated. The investigation is carried out in an air flow with a Mach number of 8. It is shown that, for a hydromagnetic interaction parameter on the order of 0.1, the slope angle of the shock wave can be increased by 10°. Experiments are conducted for the case when the flow is ionized by an electron beam or by a pulsed electric discharge. Good agreement between experimental and numerical results is obtained for both ways of ionization if the Joule heating of the gas is insignificant. The conclusion is drawn that the way of providing a nonequilibrium conductivity of the flow has a minor effect on the position of the oblique shock wave near the wedge with the hydromagnetic interaction parameter being the same.     

Role of shock waves in initiating the detonation of pentaerythritol tetranitrate by a pulsed electron beam

The results of measurements of the velocity of shock waves generated in pressed pentaerythritol tetranitrate samples by a pulsed electron beam (0.25 MeV, 15 J/cm², and 20 ns) and of the velocity of expansion of the explosion products into vacuum are presented. It was demonstrated that, during the interaction of the electron beam with pentaerythritol tetranitrate, it experiences decomposition accompanied by a pressure rise high enough to produce a shock-wave initiation of the sample.     

多孔脆性介质冲击波压缩破坏的细观机理和图像

本文采用一种具有良好定量性质的离散元模型研究了带孔洞的各向同性脆性介质在细观尺度上的压缩破坏特征. 通过对孤立孔洞、三种简单的孔洞排布方式和大量孔洞随机排布等几种情况的模拟, 认识到了剪切破坏和局域拉伸破坏是冲击波压缩下多孔介质的基本破坏模式; 孔洞之间的损伤贯通会促进孔洞在较低应力下发生塌缩, 但损伤区的应力松弛过程却会对一定范围内的介质起到损伤屏蔽作用; 不同区域中损伤促进和损伤屏蔽的综合效果是在多孔脆性介质中形成一种高损伤区与低损伤区间错排布的奇特损伤分布. 本文的研究结果为深入理解脆性材料冲击波压缩破坏的演化过程和机理提供了细观尺度上的初步物理图像.     

激光烧蚀水下金属产生冲击波和空泡效应的研究

采用自行研制的高灵敏度光束偏转测试系统,对脉冲激光烧蚀水下金属产生的等离子体冲击波和空泡效应进行了实验研究。实验得到了激光等离子体冲击波的传播规律、冲击波与激光空泡的分离过程、空泡的脉动特性以及空泡溃灭冲击波的形成机制。结果表明,空泡最大和最小泡径、振荡周期均随着脉动次数的增加呈减小趋势,且减小幅度较大。最小收缩泡径由泡能和腔内含气量共同决定。在同一次脉动过程中,空泡膨胀所需的时间明显大于收缩所需的时间。     

强流重离子束驱动的高能量密度物理研究进展

强流高能离子束可以准等容加热任何高密度样品,制备出尺度大、状态均匀、内部无冲击波的高能量密度物质,为实验室研究高能量密度物理提供了一种独特的新手段。介绍了国内外典型的强流重离子加速器装置及其与高能量密度物理相关的关键参数设计和研究规划;展示了基于粒子和流体模拟的离子束驱动高能量密度物质产生和状态演化规律进展;介绍了一套兼具高时空分辨和高穿透力的高能电子成像诊断技术;分析了中低能区离子束与等离子体相互作用过程中的碰撞和电荷交换微观机制,以及激光加速超短超强离子束在等离子体中的非线性输运和欧姆能损机制。     

纳米陶瓷粉末在爆炸压实过程中的破碎行为研究

 在爆炸压实过程中，纳米颗粒所受冲击载荷发生显著变化的时间远远大于应力波传过颗粒特征长度所用时间；同时，陶瓷颗粒在爆炸冲击过程中主要表现为脆性。基于以上两个事实提出了弹性假设，推导了颗粒在压实过程中的受力状态。回顾了判断脆性材料破坏的三个准则，即Hugonoit弹性极限、动态屈服强度和理论剪切强度，并从这三种判据的交集值出发来判断爆炸压实过程中陶瓷颗粒是否有发生破碎的可能。通过具体计算得出颗粒内存在两个最大剪应力的位置：一个位置发生在距颗粒接触面0.5 nm范围以内，此处剪应力最大；另一个位置发生在距接触面较远处。这一结果为解释陶瓷粉末颗粒在爆炸压实过程中存在塑性行为和破碎行为提供了理论依据。     

Experimental study of the formation of nonlinear acoustic waves in focused beams

The shock wave formation in focused beams produced by spherical hydroacoustic transducers with different apertures and an operating frequency of 3 MHz, as well as in weakly divergent high-intensity beams of the same frequency, is studied experimentally. The profiles of the received signals are analyzed for different receiving points in the acoustic beam and for different combinations of nonlinear and diffraction effects. It is found that the distortion of the initial waveform (i.e., of the compression and rarefaction phases) is asymmetric. The asymmetry of the wave profile in a focused beam is more pronounced than that in a quasi-plane wave while the asymmetric distortion of the high-frequency carrier causes an asymmetric distortion of the pulse envelope. The angular characteristics of the difference-frequency waves produced by parametric sound radiators are compared using both focused and weakly divergent beams of pump waves. The experiments also show that the appearance of a bubbly phase screen in the region before the point of the shock formation either shifts this point to greater distances or makes the discontinuity formation impossible. Results illustrating the changes that occur in the shock wave characteristics when the bubbly phase screen is placed in the region of the fully developed shock are presented.