Early acceleration of electrons and protons at the nonrelativistic quasiparallel shocks with different obliquity angles

The early acceleration of protons and electrons in the nonrelativistic collisionless shocks with three obliquities are investigated through 1D particle-in-cell simulations. In the simulations, the charged particles possessing a velocity of 0.2c flow towards a reflecting boundary, and the shocks with a sonic Mach number of 13.4 and an Alfven Mach number of 16.5 in the downstream shock frame are generated.In these quasi-parallel shocks with the obliquity angles θ = 15°, 30° and 45°, some of the protons and the electrons can be injected into the acceleration processes, and their downstream spectra in the momentum space show a power law tail at a time of 1.89 × 10^5ω^-1pe, where ωpe is the electron plasma frequency.Moreover, the charged particles reflected at the shock excite magnetic waves upstream of the shock. The shock drift acceleration is more prominent with a larger obliquity angle for the shocks, but the accelerated particles diffuse parallel to the shock propagation direction more easily to participate in the diffusive shock acceleration. In the early acceleration stage, more energetic protons and electrons appear in the downstream of the shock for θ = 15° compared with the other two obliquities. Moreover, in the upstream region, the spectrum of the accelerated electrons is the hardest for θnB = 45° among the three obliquities, whereas the proton spectra for θnB = 15° and 45° are similar as a result of the competition of the effectiveness of the shock drift acceleration and the diffusive shock acceleration.

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.

Ion Acceleration in Laser-Plasma Interaction: Shock, Sheath, and Scaling

在激光血浆相互作用的离子加速上的一些笔记和评价被给，特别地为吃惊的含意，鞘并且可伸缩。一个简单模型被吃惊和鞘的联合为离子加速建议。在最大的离子精力和激光参数之间的获得的可伸缩的关系(力量，脉搏持续时间)也血浆参数(血浆密度)，例如 E 离子，最大 P 7/12 L , E 离子，最大τ 1/3 L ,和 E 离子，最大 n 2/3 e ,与以前的工作相比。模型和结果的一些缺乏和含意被讨论。

Effect of Thermal Shock Process in Accelerated Environment Spectrum on the Fatigue Life of 7B04-T6 Aluminum Alloy

The effect of thermal shock, in an accelerated-corrosion environment spectrum, on the fatigue and corrosion behavior of 7B04-T6 aluminum alloy, was determined. The environment spectrum consists of two modules, namely： salt-spray corrosion and thermal shock. The effect of thermal shock on the mechanical properties was determined via tensile tests; SEM, DCS, and XRD were used to determine the effect of thermal shock on the corrosion products. In addition, the corrosion resistance of the products was ascertained through electrochemical testing. The results show that the mechanical properties and fatigue life of the aluminum alloy will decline with prolonged thermal shock time. The thermal shock process may result in denser surface corrosion products than those formed on the no thermal shock specimens, and transformation of some Al（OH）_3 into Al OOH. Al OOH may have resulted in improved corrosion resistance and hence a lower decrease in the fatigue life after corrosion, compared with that of the no thermal shock specimen. Repeated corrosion/thermal shock may have delayed further decease in the fatigue life. Therefore, selection of an appropriate equivalent thermal shock temperature and time was essential for designing the environmental spectrum.

Effect of the magnetization parameter on electron acceleration during relativistic magnetic reconnection in ultra-intense laser-produced plasma

Relativistic magnetic reconnection(MR)driven by two ultra-intense lasers with different spot separation distances is simulated by a three-dimensional(3D)kinetic relativistic particle-in-cell(PIC)code.We find that changing the separation distance between two laser spots can lead to different magnetization parameters of the laser plasma environment.As the separation distance becomes larger,the magnetization parameterσbecomes smaller.The electrons are accelerated in these MR processes and their energy spectra can be fitted with double power-law spectra whose index will increase with increasing separation distance.Moreover,the collisionless shocks’contribution to energetic electrons is close to the magnetic reconnection contribution withσdecreasing,which results in a steeper electron energy spectrum.Basing on the3D outflow momentum configuration,the energetic electron spectra are recounted and their spectrum index is close to 1 in these three cases because the magnetization parameterσis very high in the 3D outflow area.

The Origin and Acceleration of ~3He and Heavy Ions in the 2000 July 14 Event

According to the evolutionary properties of the flare, halo coronal mass ejection （CME）, enrichments of 3He ions in the energy range of 3.5-26 MeV nucl^-1 and Ne, Mg, Si and Fe ions in the energy range of 8.5-15 MeV nucl^- 1, we argue that the 3He and heavy ions originate in the middle corona （-0.1-1 R⊙） with well-connected open field lines to the Earth, where the magnetic reconnection leads to acceleration of the electrons and the production of type-ll burst during the decay phase of the soft X-ray emission. The acceleration of 3He and heavy ions may have been accomplished in two stages： first H-He ion-ion hybrid waves may be easily excited by the energetic electron beams produced in the middle corona, and these waves are preferentially absorbed by ZHe and heavy ions due to their frequency being near the fundamental gyro frequency of the ZHe ions and harmonic gyro frequency of Ne, Mg, Si and Fe ions. These preheated ions escape into interplanetary space along the open field lines and may be further accelerated to tens of MeV nucl^- 1 by CME-driven shock. The theoretical calculations show that the ZHe and heavy ions may be accelerated to the energy of - MeV nucl^-1 by the ion-ion hybrid waves and be further accelerated to the energy of -100 MeV nucl^-1 by the shock wave： these are basically consistent with the observations.

Ion dynamics in laser-produced collisionless perpendicular shock: one-dimensional particle-in-cell simulation

Recently, perpendicular shocks have been generated in laboratory experiments by the interaction between a laser-produced supersonic plasma flow and a magnetized ambient plasma. Here, we explore the ion dynamics and the formation of such kinds of shock with a one-dimensional(1D)particle-in-cell simulation model using achievable parameters for laser experiments. A small part of the ambient ions is first reflected by the laser-driven piston. These piston-reflected ions interact with the upstream plasma and form a shock then. By analyzing the contribution of the electric force and the Lorentz force during the reflection, shock-reflected ions are found to be accelerated by two different mechanisms: shock drift acceleration and shock surfing acceleration,where shock drift acceleration is the dominant one. Very few ions are reflected twice by the shock and accelerated to a large velocity, implying that a more energetic population of ions can be observed in future experiments.

冲击加速度国际关键比对与参考值确定

介绍了中国计量科学研究院主导的冲击加速度国际关键比对(CCAUV.V-K4)。分析了比对样品冲击测量链各部分动态特性,并与实验室实际校准的冲击加速度激励信号相结合,说明了作为测量结果的冲击灵敏度与冲击激励的关系。针对比对参考值及其相应不确定度计算的问题,详细说明了3种方法的计算过程,包括国际比对推荐的计算方法和2种基于贝叶斯推断的计算方法。特别对基于贝叶斯统计的方法,结合实际校准过程的信息,采用了不同的统计模型和先验分布,利用马尔科夫链-蒙特卡洛(MCMC)数值计算方法得到了比对参考值的后验分布。对3种方法计算结果的进行了比较,并说明了3种方法的统一性及优缺点。

随机振动加速度响应谱及与冲击等效性分析

目的 获得随机振动的加速度响应谱,提升随机振动与冲击的等效性分析精度。方法 首先,基于维纳-辛钦定理,推导单自由度系统在随机振动基础激励作用下加速度响应均方值的通用表达式;其次,分别推导单自由度系统在理想白噪声和限带非均匀谱随机振动基础激励作用下的加速度响应均方值;再次,基于3σ准则,推导限带非均匀谱随机振动的3σ加速度响应谱;最后,基于加速度响应等效,通过将装备随机振动条件的3σ加速度响应谱与冲击条件的冲击响应谱进行等效性分析,对GJB 150.18A—2009中的冲击试验剪裁条件进行精细优化。结果 精细优化后,可有效改善冲击试验剪裁条件的工程实施精度。结论 获得了限带非均匀谱随机振动的3σ加速度响应谱,并基于此对GJB 150.18A—2009中的冲击试验剪裁条件进行了精细优化,对于装备合理剪裁冲击试验具有借鉴意义。

Characteristics of response spectra for long-periods of main-shock recordings of the Chi-Chi earthquake

Current practice uses predictive models to extrapolate long-period response spectra based on far-field recordings in moderate and weak earthquakes. However, the spectra are not long enough and the data are often not reliable, which means that the seismic design code cannot accurately define seismic design requirements for long-period structures. The near-field recordings in the main-shock of the Chi-Chi earthquake have a large signal-to-noise ratio （SNR）, which makes them suitable for studying the long-period acceleration response spectrum up to 20 sec. The acceleration response spectra from 246 stations within 120 km of the causative fault are statistically analyzed in this paper. The influence of distance and site conditions on long-period response spectrum is discussed, and the shapes of the amplification spectra are compared with the standard spectra specified in the seismic design code of China. Finally, suggestions for future revisions to the code are proposed.

Energy spectral property in an isolated CME-driven shock

Observations from multiple spacecraft show that there are energy spectral ＂breaks＂ at 1-10 MeV in some large CME-driven shocks. However, numerical models can hardly simulate this property due to high computational expense. The present paper focuses on analyzing these energy spectral ＂breaks＂ by Monte Carlo particle simulations of an isolated CME-driven shock. Taking the 2006 Dec 14 CME-driven shock as an example, we investigate the formation of this energy spectral property. For this purpose, we apply different values for the scattering time in our isolated shock model to obtain the highest energy ＂tails,＂ which can potentially exceed the ＂break＂ energy range. However, we have not found the highest energy ＂tails＂ beyond the ＂break＂ energy range, but instead find that the highest energy ＂tails＂ reach saturation near the range of energy at 5 MeV. So, we believe that there exists an energy spectral ＂cut off＂ in an isolated shock. If there is no interaction with another shock, there would not be formation of the energy spectral ＂break＂ property.

Analysis of the CME-driven shock from the SEP event that occurred on 2006 December 14

In a solar flare or coronal mass ejection （CME）, observations of the subse- quent interplanetary shock provide us with strong evidence of particle acceleration to energies of multiple MeV, even up to GeV. Diffusive shock acceleration is an efficient mechanism for particle acceleration. For investigating the shock structure, the energy injection and energy spectrum ofa CME-driven shock, we perform a dynamical Monte Carlo simulation of the CME-driven shock that occurred on 2006 December 14 using an anisotropic scattering law. The simulated results of the shock＇s fine structure, par- ticle injection, and energy spectrum are presented. We find that our simulation results give a good fit to the observations from multiple spacecraft.

Experimental Study of Structure Shock Vibration in Soil Caused by Explosion of Conventional Weapons

When hitting underground structures directly or exploding in rock-soil media near underground structures, the conventional weapons with large charge weight will make underground structures be subjected to strong shock vibration and cause personal casualty and damage of precision electronic equipments. The shock vibration has become one of the cardinal killing means of weapons. However, the existing methods of predicting structure shock vibration are limited evidently. In this paper the coupling coefficient of acceleration in clayey soil is obtained firstly. Subsequently based on repeated experiments of chemical explosion, after dimension analysis and by using method of multivariate stepwise regression, the calculation formulae of shock vibration acceleration for the underground structure are obtained finally. The formulae consider top and side explosion respectively, taking into account the effects of penetration depth, charge weight, distance to explosion center, rock-soil media, size of structure and buried depth. They are easy to use with high practicability and degree of confidence, and can provide credible evidence for prediction of shock vibration and vibration isolating design of underground structure.

VISIOMETRICS OF 2D SHOCK-PLANAR S/F/S CURTAIN INTERACTIONS: VORTEX DOUBLE LAYERS, VORTEX PROJECTILES AND DECAYING STRATIFIED TURBULENCE

Vortex double layers (VDLs) and vortex projectiles (VPs) are the essential coherent structures which emerge in the shock excited (s/f/s) planar parallel "curtain" simulations of a 2D shock tube with PPM. These opposite signed layers, formed by shock induced baroclinic deposition of vorticity, "ind" and are strongly affected by secondary reflected shocks and vortex interactions. In our visiometric mode of working, we quantify several of these processes and introduce time epochs to discuss the emerging phenomena and normalizations to scale (collapse) the data at M =1.5 and 2.0. This versatile configuration, easily obtained in the laboratory, allows us to study the formation, evolution and reacceleration of VPs and stratified turbulence and mixing.

加速剂对铝基覆铜板通孔电镀铜的影响

在由70 g/L硫酸铜、200 g/L浓硫酸、60 mg/L盐酸、200 mg/L聚乙二醇(PEG6000)和1 mg/L健那绿B(JGB)组成的基础镀液中分别添加聚二硫二丙烷磺酸钠(SPS)、3-巯基-1-丙磺酸钠(MPS)和N,N-二甲基二硫代甲酰胺丙烷磺酸钠(DPS)作为加速剂。通过计时电位曲线测试和热冲击试验,研究了不同加速剂对通孔电镀铜的影响。结果表明,镀液中添加2.5 mg/L SPS或9 mg/L DPS作为加速剂时,镀液的深镀能力显著提高,所得Cu镀层的抗热冲击性能合格。

反弹对撞式冲击放大器机理研究

为了在传统跌落冲击试验台上开展强冲击试验,以获得更高的加速度峰值。采用动态接触理论与经典碰撞理论相结合的方法,考虑能量损失,引入碰撞恢复系数,建立反弹对撞式冲击放大器的运动学模型,推导了加速度及其放大倍数计算公式,研究了预留间隙、弹力绳刚度对冲击放大的影响规律。设计实验装置并进行试验,验证了理论模型的可行性和有效性。结果表明:理论计算与实验结果较吻合,最大误差约为7%;冲击放大台的最大加速度可达3780 g,加速度放大约13.5倍;存在一个理想预留间隙,使放大台加速度取得最大值,且选取较大跌落高度及理想预留间隙,更利于冲击放大;小刚度弹力绳对加速度具有一定的放大作用,但与预留间隙相比,影响较小。

脉冲爆震燃烧室内缓燃向爆震转捩数值模拟

为了研究脉冲爆震发动机燃烧室内火焰加速及缓燃向爆震转捩过程,利用7组分8反应的氢气详细化学反应机理进行了2维数值模拟。结果表明:在火焰传播的初始阶段,障碍物、旋涡与火焰的相互作用是主导火焰加速的主要因素。在燃烧区域产生的膨胀波向前传播并诱导未燃混气流动;障碍物后的回流区及障碍物顶端脱落的旋涡使火焰面拉伸、卷曲,增加火焰面面积,同时提高燃烧放热强度,使火焰传播速度加快。在火焰发展的后期阶段,激波与障碍物的相互作用会使脱落在已燃混气中的未燃混气微团发生局部爆炸,产生新的激波进一步推动火焰加速,缩短火焰锋面与前导激波的距离。由于交错型障碍物增加了火焰传播的距离,其缓燃向爆震的转捩时间比采用对称型障碍物时的更长。

基于损伤等效的航空发动机加速任务试车谱编制方法

加速任务试车是发动机在地面试车台架上进行的一种缩短了试车时间、与长期寿命试车等效的试车方法,其核心是损伤等效。本文建立了一种基于损伤等效的航空发动机加速任务试车谱编制方法。对反映外场服役载荷特征的长期寿命试车谱进行统计分析,获得需要加速的小载荷循环和低功率状态等载荷信息;采用损伤等效的方法对低循环疲劳、蠕变等特征载荷进行等效加速;对加速后的载荷片段进行编排,获得加速任务试车谱。利用涡轮盘用典型高温合金材料(GH4169)的标准试样开展了长期寿命试车谱和加速任务试车谱下的损伤对比试验,试验结果表明,所编制的加速任务试车谱与长期寿命试车谱造成的结构损伤(寿命)误差为-7.61%,实现了损伤等效的目标。

Supersonic gas jet stabilization in laser–plasma acceleration

Supersonic gas jets generated via a conical nozzle are widely applied in the laser wakefield acceleration of electrons.The stability of the gas jet is critical to the electron injection and the reproducibility of the wakefield acceleration.Here we discussed the role of the stilling chamber in a modified converging-diverging nozzle to dissipate the turbulence and to stabilize the gas jets.By the fluid dynamics simulations and the Mach-Zehnder interferometer measurements,the instability originating from the nonlinear turbulence is studied and the mechanism to suppress the instability is proposed.Both the numerical and experimental results prove that the carefully designed nozzle with a stilling chamber is able to reduce the perturbation by more than 10% compared with a simple-conical nozzle.