The limiting compression in single shocks for sp metals

The slope of the linear curve relating shock velocity and particle velocity in shock wave experiments has been examined by the pseudopotential energy band method for sp metals. The limiting density ration resulting from this linear relation is interpreted by defining a shock “hard core” for single shocks and its relation to Ashcroft's core radius is examined.     

聚四氟乙烯动态特性的实验研究

 在10~55 GPa的高压范围用化爆装置、采用阻抗匹配法测得了聚四氟乙烯（初始密度ρ₀=2.19 g/cm³）的冲击波速度D和波后粒子速度u之关系为：D=2.10+1.62u（mm/μs）。在0.2~3 GPa的低压范围用气炮装置、采用电磁速度计测量了材料内加、卸载过程的拉格朗日粒子速度波形，获得的冲击加载D-u关系为：D=1.24+3.72u-1.94u²（mm/μs）。实测卸载曲线和加载冲击绝热线接近一致，残余应变似乎不存在或者说很小；弹性区段很不明显，聚四氟乙烯本质上呈现出塑性性质。     

磁驱动准等熵压缩下单晶氟化锂的光学特性

以"阳"加速器和PTS装置为驱动源,开了展单晶氟化锂(LiF,通光方向[100])窗口材料在准等熵压缩下的光学特性实验研究。应用全光纤激光多普勒探针系统(DPS,激光波长1550nm)同时测量了Ly12铝材料电极加窗和未加窗的后界面速度历史,结合窗口材料修正方法获取了单晶氟化锂窗口材料在实验条件下折射率随密度的变化和界面粒子速度修正因子。每次实验可获取窗口材料样品的连续加载历史数据,进而处理得到LiF窗口材料在近50GPa准等熵压力范围内的修正因子。结合拟合的线性关系,进一步处理获得了在实验过程中折射率随密度的变化。将这些实验结果与D.E.Fratanduono,Y.Ma,B.J.Jensen的对应数据比较,其中与光子多普勒测速系统(PDV,1550nm)测量结果基本相符,不确定度与多次冲击实验得到的结果相当。     

纳秒激光冲击加载的全过程诊断

 与传统的冲击加载方式相比,激光驱动试样具有微尺寸（直径小于1 mm,厚度约10 μm）、超短作用过程（纳秒量级）等特点,但其速度变化历史的实时诊断颇为困难,因此发展适用于激光驱动的高时空分辨率的实时测试技术是十分重要和有价值的。采用桌面式脉冲Nd:YAG激光器作为加载平台,发展了激光加载下的小焦点多普勒光纤探针测量系统（焦斑直径约200 μm,时间分辨力约50 ps）,成功实现了从激光脉冲驱动微尺寸飞片飞行直至撞击Z-切石英试样的全过程实时诊断。实验结果显示,将6 μm 厚Al箔飞片驱动至2.48 km/s时,撞击Z-切石英试样的粒子速度为1.27 km/s,与Hugoniot理论计算结果相符,表明该测试技术是可靠、有效的;多层薄膜靶结构设计（基底/烧蚀层/硅油/Al箔）可提升激光与靶物质的能量耦合效率,使飞片保持更好的宏观完整性。为开展超短脉冲激光加载下材料动态特性研究提供了一种有效的技术途径。     

冲击压缩下单晶LiF高压声速及卸载路径研究

 采用二级轻气炮加载手段，在5~79.1 GPa冲击压力范围内，利用加窗VISAR技术对氟化锂（LiF）单晶样品进行了研究，得到了不同冲击压力下的纵波声速、体积声速以及卸载路径。实验结果显示：单晶LiF沿冲击绝热线的Lagrange纵波声速随粒子速度呈线性变化；在5~79.1 GPa冲击压力下，单晶LiF并未发生熔化及其它相变；卸载路径及速度剖面弹塑性明显。     

钽在冲击载荷下的动态力学特性

 在对称碰撞实验中,用VISAR测试系统记录了自由面粒子速度剖面。结合材料常压弹性纵波声速的测量,利用冲击加载的双波结构,测量了钽在30 GPa以内的冲击波速度,给出了线性相关性非常好的D-u_p 关系,并与高压下的测量结果作了比较。同时对由自由面粒子速度剖面来计算层裂强度的模型进行了讨论,发现模型差异对钽的层裂强度的影响超过30%。     

Fe73.5Cu1Nb3Si13.5B9非晶合金的激波纳米晶化速率和晶化度的对比研究

对Fe735Cu1Nb3Si135B9等非晶合金进行了退火和激波诱导两种方式的晶化实验以及XRD和DSC分析.着重对合金的晶化速率和晶化度等特性展开了研究和讨论.进一步证实了激波纳米晶化是一种包含着新机理的寓意丰富的晶化现象.也再次验证了作者曾经提出过的“激波流化相变”模型的合理性. 关键词： 非晶合金 激波 纳米晶化     

用于冲击诊断的成像速度干涉仪

为了诊断测量激光驱动冲击波,研制了具有空间分辨力的成像型速度干涉仪.该干涉仪主要包括输入部分、像传递部分及干涉部分,探测光采用波长为532 nm的单纵模激光.在靶位放置一分线板,经过测量,其空间分辨力小于10μm.基于天光KrF准分子激光系统的参数,设计并自制含有烧蚀层的单台阶金属靶,利用成像型速度干涉仪测量到了金属铝...     

一种新的线成像激光干涉测速系统

 设计并搭建了一种新的线成像激光干涉测速系统,用于小样品材料的冲击波诊断或飞片速度测量。系统采用梳状干涉条纹做为信号载体,利用1维光纤阵列＋光电倍增管＋数字示波器替代变像管扫描相机作为记录设备,记录伪推挽四路干涉信号,实现1 ns时间分辨和86 μm空间分辨。用它测量了脉冲激光驱动铝膜飞片的速度场,获得对比度较好的信号,数据处理结果揭示了飞片加速过程将近20 ns,飞片的平面度为14.8 mrad。实验证明,该线成像激光干涉测速系统具有一定实用性。     

Second Hugoniot relationship for solids

The term second Hugoniot is used to describe a locus of states directly attainable by shock compression beginning with an initial state that has itself been achieved by shock compression. For many materials the principal Hugoniot is linear in the shock velocity-particle velocity [U_s — u_p] representation. A second Hugoniot for such materials is not linear in this representation, but the nonlinear effects can often be neglected if the compressions are not too great. These results are based on the Mie-Grüneisen equation of state and are more or less independent of the explicit functional dependence of the Grüneisen parameter. A criterion to evaluate the magnitude of nonlinear effects is posed and Mg and Pb are treated as examples. Calculated second Hugoniots are compared with experimental results for regular reflection in Mg, Pb and U. For these materials nonlinear effects are not important from a practical standpoint for final volumetric compressions to roughly two-thirds of the initial volume. Some future experimental work is also suggested.     

Bi在固液混合相区的冲击参数测量及声速软化特性

冲击相变与熔化作为材料特性的一项重要研究内容,对于多相物态方程构建具有重要意义.本文利用追赶稀疏原理和阻滞法,基于火炮加载技术获得了17.3—28.3 GPa范围内纯铋(Bi)的高精度声速数据和Hugoniot参数,分析了声速软化规律,得到固-液混合相区Bi材料声速随压力的近似线性递减关系C=3.682-0.015p,并进一步确定Bi的冲击熔化压力区间为18—27.4 GPa.同时,Bi/Li F界面速度剖面的预期平台段在固液混合相区表现出渐进爬升的异常特征,分析认为,该现象与Bi材料的非均匀熔化动力学行为及冲击熔化完成时间尺度较长有关.     

Velocity and timing of multiple spherically converging shock waves in liquid deuterium

The fuel entropy and required drive energy for an inertial confinement fusion implosion are set by a sequence of shocks that must be precisely timed to achieve ignition. This Letter reports measurements of multiple spherical shock waves in liquid deuterium that facilitate timing inertial confinement fusion shocks to the required precision. These experiments produced the highest shock velocity observed in liquid deuterium (U(s) = 135 km/s at ～2500 GPa) and also the first observation of convergence effects on the shock velocity. Simulations model the shock-timing results well when a nonlocal transport model is used in the coronal plasma.     

Effects of density profile and multi-species target on laser-heated thermal-pressure-driven shock wave acceleration

The shock wave acceleration of ions driven by laser-heated thermal pressure is studied through one-dimensional particle-in-cell simulation and analysis. The generation of high-energy mono-energetic protons in recent experiments （D. Haberberger et al., 2012 Nat. Phys. 8 95） is attributed to the use of exponentially decaying density profile of the plasma target. It does not only keep the shock velocity stable but also suppresses the normal target normal sheath acceleration. The effects of target composition are also examined, where a similar collective velocity of all ion species is demonstrated. The results also give some reference to future experiments of producing energetic heavy ions.     

Shock wave propagation in soda lime glass using optical shadowgraphy

Propagation of shock waves in soda lime glass, which is a transparent material, has been studied using the optical shadowgraphy technique. The time-resolved shock velocity information has been obtained (1) in single shot, using the chirped pulse shadowgraphy technique, with a temporal resolution of tens of picoseconds and (2) in multiple shots, using conventional snapshot approach, with a second harmonic probe pulse. Transient shock velocities of (5–7) × 10⁶ cm/s have been obtained. The scaling of the shock velocity with intensity in the 2 × 10¹³–10¹⁴ W/cm² range has been obtained. The shock velocity is observed to scale with laser intensity as I^0.38. The present experiments also show the presence of ionization tracks, generated probably due to X-ray hotspots from small-scale filamentation instabilities. The results and various issues involved in these experiments are discussed.     

冲击压缩性的高精度测量技术

 详细介绍了在冲击压缩性测量中为提高冲击波速度测量精度，在减小样品尺寸测量的相对误差以及保证安装过程不破坏其原有加工精度的技术措施。还介绍了利用多路时间间隔测量仪记录冲击波传播时间时，如何减小传输误差以及利用探针的合理布局对冲击波阵面的倾斜和弯曲畸变进行修正的方法。此外，介绍了利用光纤技术同时获得冲击波速度和冲击温度信息的技术。采用上述技术措施后使弹丸速度的测量误差约为0.2%~0.4%，冲击波速度的测量误差约为~1%。     

利用VISAR测量LY12铝在冲击压缩下的声速

 介绍了利用VISAR技术测量受冲击压缩LY12铝的高压声速的方法。平板对称碰撞实验在冲击波物理与爆轰物理实验室的二级轻气炮上进行,峰值应力约为20、32、55和71 GPa。每发实验中,VISAR同时使用三种条纹常数测量LY12铝和单晶LiF窗口的界面粒子速度剖面。从三种条纹常数计算的界面粒子速度剖面相互符合,完全一致。实验信号具有很高的信噪比,表明样品与窗口之间的界面连结和处理技术非常成功。这种测量技术不仅能够得到初始加载应力下的纵波声速,而且能够得到声速沿着卸载路径的变化。将声速的塑性段外推到初始冲击加载压力即得到该压力下的体积声速。LY12铝的声速测量结果与假定ργ为常数条件下用Mie-Grüneisen状态方程计算的结果符合得很好。     

成像型任意反射面速度干涉仪研制

成像型任意反射面速度干涉仪是激光驱动冲击波研究的重要诊断设备,主要应用于惯性约束聚变脉冲整形实验、高压状态方程实验研究和材料特性研究.基于传统任意反射面速度干涉仪的特点,研制了一台基于神光Ⅲ原型装置的成像型任意反射面速度干涉仪,该系统可用于测量自由面速度及透明介质中的冲击波速度.给出了成像型任意反射面速度干涉仪的详细设计要点.对系统性能进行了分析及测试,结果表明时间分辨优于30 ps,物方空间分辨约为10 μm,测速范围为6～45 km/s.     

Analysis of the stability and density waves for traffic flow

In this paper, the optimal velocity model of traffic is extended to take into account the relative velocity. The stability and density waves for traffic flow are investigated analytically with the perturbation method. The stability criterion is derived by the linear stability analysis. It is shown that the triangular shock wave, soliton wave and kink wave appear respectively in our model for density waves in the three regions: stable, metastable and unstable regions. These correspond to the solutions of the Burgers equation, Korteweg－de Vries equation and modified Korteweg－de Vries equation. The analytical results are confirmed to be in good agreement with those of numerical simulation. All the results indicate that the interaction of a car with relative velocity can affect the stability of the traffic flow and raise critical density.     

Hierarchical model for the scale-dependent velocity of waves in random media

Elastic waves of short wavelength propagating through the upper layer of the Earth appear to move faster at large separations of source and receiver than at short separations. Existing perturbation theories predict a linear increase of the velocity shift with increasing separation and cannot describe the saturation of the velocity shift at large separations that is seen in computer simulations. We point out that this nonperturbative problem can be solved using a model developed originally for the study of directed polymers. The saturation velocity is found to scale with the four-thirds power of the root-mean-square amplitude of the velocity fluctuations, in good agreement with the computer simulations.     

成像型任意反射面速度干涉仪的散斑抑制

成像型任意反射面速度干涉仪(VISAR)是激光驱动聚变实验中诊断冲击波速度的重要设备。由于采用了激光照明靶面的方式,所获得的速度条纹图中不可避免有激光散斑的干扰,严重影响动态条纹的质量。介绍了该系统的激光散斑形成原因和散斑对速度分析的影响,提出了一种频谱面滤波的方式去除高频散斑噪声的方法,并通过搭建散斑光路、合理设置滤波孔位置和大小,对该方法进行了验证。结果表明,该方法对影响条纹图的高频散斑噪声具有抑制作用,适合应用于成像型VISAR系统。