轴向剪切流对Z箍缩等离子体瑞利-泰勒不稳定性的抑制

利用理想磁流体力学模型对有轴向剪切流的Z箍缩等离子体不稳定性进行了分析。给出了可压缩模型的色散关系,分别对可压缩及不可压缩模型中轴向剪切流对Z箍缩等离子体瑞利-泰勒不稳定性的抑制作用进行了比较,讨论了可压缩性对含有轴向剪切流系统不稳定性的影响。结果表明,可压缩性能够减缓瑞利-泰勒P凯尔文-亥姆霍兹(RTPKH)模扰动的增长,因而使得轴向剪切流对系统不稳定性的抑制作用表现得更为突出。计算结果还说明,在RT不稳定性线性增长阶段,等离子体温度较低,使用可压缩模型能够更真实地描述系统的状态。     

Effects of compressibility on the Rayleigh-Taylor instability in Z-pinch implosions

1 IntroductionZ-pinch imploding plasma thin shells formed bygas puffs,cylindrical foils,and wire arrays can radiatehundreds of kilojoules of soft X-rays.They are highefficient and compact devices which have wideapplied prospects,specially,as intense X-ray…     

Finite Larmor radius and Hall effects on thermal instability of a compressible plasma

The effects of compressibility, finite Larmor radius (FLR) and Hall currents are considered on the thermal instability of a plasma in the presence of a uniform horizontal magnetic field. For stationary convection, the compressibility has a stabilizing effect whereas FLR and Hall currents have stabilizing as well as destabilizing effects. For (C _pβ/g)<1, the system is stable. The magnetic field, FLR and Hall currents introduce oscillatory modes in the system for (C _pβ/g)>1.     

瑞利-泰勒不稳定问题的光滑粒子法模拟研究

提出了一种适用于模拟多相流的光滑粒子法,该方法对密度方程在交界面处的离散格式进行了修正以适应多相流所涉及的大密度比问题,在不同相粒子之间施加了很小的排斥力以防止粒子穿透交界面,并采用了最新发展的双曲型光滑函数以消除应力不稳定问题.应用该多相流光滑粒子法模拟研究了单模态和多模态瑞利-泰勒不稳定问题.通过与文献中结果的对比研究表明:在模拟瑞利-泰勒不稳定问题时,本文方法的结果明显优于文献中的大部分光滑粒子法模拟结果,与Grenier等(2009 J.Comput.Phys.228 8380)的结果相当,但本文方法比Grenier等的方法简单方便.对于单模态瑞利-泰勒不稳定问题,研究了交界面的形态,涡结构的演化过程以及贯穿深度随时间的变化关系.对于多模态瑞利-泰勒不稳定问题,研究了交界面演化过程中小尺度结构合并成大尺度结构的过程,水平方向的平均密度随高度的变化关系,以及贯穿深度随时间的变化关系.     

Rayleigh-Taylor instability of multi-fluid layers in cylindrical geometry

Rayleigh-Taylor instability of three fluid layers with two interfaces in cylindrical geometry is investigated analytically.The growth rates and the amplitudes of perturbation on the two interfaces are obtained. The feedback factor from outer to inner interface is larger than that from inner to outer interface under the same conditions. The growth rate on the initially unstable interface is larger than the corresponding result in planar geometry for low mode perturbation. The two interfaces are decoupled for a larger mode number perturbation. The dependencies of the amplitudes of perturbation on different initial conditions are analyzed. The negative feedback effect from initially stable interface to another unstable interface is observed. In the limit of infinity inner radius and finite shell thickness, the results in planar geometry are recovered.     

可压缩与不可压缩流体中Rayleigh Taylor不稳定性的比较

 对比研究了可压缩与不可压缩流体的Rayleigh Taylor不稳定性小扰动阶段的增长速率，其中，压力是密度的任意单值函数，这个函数也即是可压缩流体的状态方程。研究表明：在相同密度分布条件下，可压缩流体的界面扰动增长速率总是比相应的不可压缩流体的界面增长率大，其相对增长率随扰动波长的增加而增大，随两种介质的声速减小而增大，在长波和易压缩流体中，相对增长率可达0.8以上。因此，在某些条件下，流体可压缩性对Rayleigh Taylor不稳定性的影响是不能忽略的。     

Influences of finite Larmor radius on wake effects and stopping power for proton moving in magnetized two-component plasma

Considering finite Larmor radius (FLR) effects, wake effects and stopping power induced by proton projectile in two-component magnetized plasma are investigated within a linear response framework. Numerical results show that, FLR lessens wake effects and stopping power, essentially through excitation of collective plasma electron modes.     

掺杂对CH样品Rayleigh-Taylor不稳定性增长的影响

在神光II激光装置上进行了辐射驱动不同掺杂样品的单模Rayleigh-Taylor(RT)不稳定性实验.结果显示:与纯碳氢(CH)样品相比,掺Br的CH样品的扰动更早、更快地进入非线性区,产生二次谐波,并且掺Br比例越高,CH样品扰动进入非线性区的时间越早,相同时刻扰动的二次谐波的幅度越高.这是因为密度梯度效应抑制了二次谐波的产生,掺Br比例越高,密度梯度标长越小;同时密度梯度效应还抑制三次谐波对基模增长的负反馈,造成基模具有更大的线性增长,导致线性饱和幅值大于经典值0.1λ.     

可压流体Rayleigh-Taylor不稳定性的离散Boltzmann模拟

使用离散Boltzmann模型模拟了可压流体系统中多模初始情况下的Rayleigh-Taylor不稳定性.该离散Boltzmann模型等效于一个Navier-Stokes模型外加一个关于热动非平衡行为的粗粒化模型.通过模拟Riemann问题:Sod激波管、冲击波碰撞和热Couette流问题验证模型的有效性,所得数值结果与解析解一致.利用该模型对界面间断随机多模初始扰动的可压Rayleigh-Taylor不稳定性进行数值模拟研究,得到不稳定性界面演化过程的基本图像.由于黏性和热传导共同作用,一开始扰动界面被"抹平",演化较慢;随着模式互相耦合而减少,演化开始加速,并经历非线性小扰动阶段和不规则非线性阶段,而后发展成典型的"蘑菇状",后期进入湍流混合阶段.由于扰动模式的耦合与发展,轻重流体的重力势能、压缩能与动能相互转化,系统先是趋于热动平衡态,而后偏离热动平衡态以线性形式增长,接着再次趋于热动平衡态,最后慢慢远离热动平衡态.     

ICF研究中的Rayleigh-Taylor不稳定性实验用靶

 概述了当前研究Rayleigh-Taylor不稳定性增长实验所用的靶型情况。从实验用靶来看，调制靶的设计正从平面向立体发展，出现了球形和柱形等新靶形，制备手段包括精密机械微加工、激光束、电子束和离子束加工、半导体工艺和微米纳米技术加工等。根据对国外新靶型的研究，结合国内工艺条件和实验需求，对国内可能采用的靶型进行了研究探索。     

Density oscillations in laser produced plasma decelerated by external magnetic field

This paper presents the dynamics as well as the stability of laser produced plasma expanding across the magnetic field. Observation of some high frequency fluctuations superimposed on ion saturation current along with structuring in the pin hole images of x-ray emitting plasma plume indicate the presence of instability in the plasma. Two type of slope in the variation of x-ray emission with laser intensity in the absence and presence of magnetic field shows appearance of different threshold intensity of laser corresponding to each magnetic field at which this instability or density fluctuation sets on. This instability has been identified as a large Larmor radius instability instead of classical Rayleigh-Taylor (R-T) instability.     

Stability analysis of viscous Z-pinch plasma with a sheared axial flow

Within the magnetohydrodynamics （MHD） frame, we analyse the effect of viscosity on magneto-Rayleigh Taylor （MRT） instability in a Z-pinch configuration by using an exact method and an approximate method separately. It is demonstrated that the plasma viscosity indeed has a stabilization effect on the MRT mode in the whole wavenumber region, and its influence increases with the perturbation wavenumber increasing. After the characteristics and feasibility of the approximate method have been investigated, we apply it to the stability analysis of viscous plasma where a sheared axial flow （SAF） is involved, and we attain an analytical dispersion relation. It is suggested that the viscosity and the SAF are complemental with each other, and a wide wavenumber range of perturbation is possible to be restrained if the SAF and the viscosity are large enough. Finally, we calculate the possible value of viscosity parameter according to the current experimental conditions, and the results show that since the value of viscosity is much less than the threshold value, its mitigation effect is small enough to be neglected. The role of the viscosity in the stabilization becomes considerable only if special techniques are so developed that the Z-pinch plasma viscosity can be increased greatly.     

黏性、表面张力和磁场对Rayleigh-Taylor不稳定性气泡演化影响的理论分析

采用理论分析的方法考察了磁场中非理想流体中Rayleigh-Taylor(RT)不稳定性气泡的演化过程,在与磁场垂直的平面中,综合考虑流体黏性和表面张力的影响,推导了二维非理想磁流体RT不稳定性气泡运动的控制方程组,给出了不同情况下气泡速度的渐近解和数值解,分析了流体黏性、表面张力和磁场对气泡发展的影响,分析结果表明:流体黏性和表面张力能够降低气泡速度和振幅,即能够抑制RT不稳定性;而磁场对RT不稳定性的影响是由非线性部分引起的,并且磁场非线性部分的方向决定了磁场是促进还是抑制RT不稳定性的发展,     

高雷诺数下非混相Rayleigh-Taylor不稳定性的格子Boltzmann方法模拟

本文采用相场格子Boltzmann方法研究了竖直微通道内中等Atwoods数流体的单模Rayleigh-Taylor不稳定性问题,系统分析了雷诺数对相界面动力学行为以及扰动在各发展阶段演化规律的影响.数值结果表明高雷诺数条件下,不稳定性界面扰动的增长经历了四个不同的发展阶段,包括线性增长阶段、饱和速度阶段、重加速阶段及混沌混合阶段.在线性增长阶段,我们计算获得的气泡与尖钉振幅符合线性稳定性理论,并且线性增长率随着雷诺数的增加而增大.在第二个阶段,我们观察到气泡与尖钉将以恒定的速度增长,获得的尖钉饱和速度略高于Goncharov经典势能模型的解析解[Phys.Rev.Lett.200288134502],这归因于系统中产生了多个尺度的旋涡,而涡之间的相互作用促进了尖钉的增长.随着横向速度和纵向速度的差异扩大,气泡和尖钉界面演化诱导产生的Kelvin–Helmholtz不稳定性逐渐增强,从而流体混合区域出现许多不同层次的涡结构,加速了气泡与尖钉振幅的演化速度,并在演化后期阶段,导致界面发生多层次卷起、剧烈变形、混沌破裂等行为,最终形成了非常复杂的拓扑结构.此外,我们还统计了演化后期气泡与尖钉的无量纲加速度,发现气泡和尖钉的振幅在后期呈现二次增长规律,其增长率系数分别为0.045与0.233.而在低雷诺条件下,重流体在不稳定性后期以尖钉的形式向下运动而轻流体以气泡的形式向上升起.在整个演化过程中,界面变得足够光滑,气泡与尖钉在后期的演化速度接近于常数,未观察到后期的重加速与混沌混合阶段.     

斜界面Rayleigh-Taylor不稳定性混合实验研究

 实验研究了不相溶流体斜界面Rayleigh-Taylor（R-T）不稳定性湍流混合区的混合不对称性特征。利用高压气体加速装有不同液体的箱体,加速度方向由轻液体指向重液体,此时界面是R-T不稳定性的。利用阴影测试技术,研究了初始倾角9°的ZnCl₂溶液/正己烷斜界面的演化规律,得出混合区内混合不对称、斜界面倾角渐增的规律。     

Cylindrical effects in weakly nonlinear Rayleigh Taylor instability

The classical Rayleigh–Taylor instability(RTI)at the interface between two variable density fluids in the cylindrical geometry is explicitly investigated by the formal perturbation method up to the second order.Two styles of RTI,convergent(i.e.,gravity pointing inward)and divergent(i.e.,gravity pointing outwards)configurations,compared with RTI in Cartesian geometry,are taken into account.Our explicit results show that the interface function in the cylindrical geometry consists of two parts:oscillatory part similar to the result of the Cartesian geometry,and non-oscillatory one contributing nothing to the result of the Cartesian geometry.The velocity resulting only from the non-oscillatory term is followed with interest in this paper.It is found that both the convergent and the divergent configurations have the same zeroth-order velocity,whose magnitude increases with the Atwood number,while decreases with the initial radius of the interface or mode number.The occurrence of non-oscillation terms is an essential character of the RTI in the cylindrical geometry different from Cartesian one.     

线性偏振激光在相对论等离子体中的调制不稳定性

从相对论等离体中电磁波的非线性色散方程出发,利用Karpman方法获得了线性偏振波模所满足的非线性控制方程,在非线性色散方程和非线性控制方程的基础上对线性偏振激光在相对论等离体中传播的调制不稳定性进行分析,给出了调制不稳定的时间增长率与扰动态波数之间的函数关系。     

A numerical study on Rayleigh-Taylor instability of aluminum plates driven by detonation

The authors,using elastic-plastic hydrodynamic code,present the Rayleigh-Taylor (RT) instability of Al plates driven by high-explosive detonation. Our numerical study assumes the material is fluid,or it is an elastic-plastic solid,and we compare the results of these simulations with the experimental data. For the numerical simulation of Rayleigh-Taylor instability of the metal driven by high-explosive detonation,the elastic-plastic effect must be assumed. The result of the simulation is different from the e...     

单层钨丝阵Z箍缩内爆不稳定性特征实验研究

基于激光阴影像,研究了直径为8 mm的钨丝阵在滞止阶段的不稳定性发展。实验结果表明,在消融阶段早期,不稳定性扰动的主导波长为0.2 mm。在内爆后期和滞止阶段,不稳定主导波长迅速向长波长方向发展。在功率峰值前后,扭曲不稳定性特征开始出现,在滞止等离子体柱达到最小收缩直径后,辐射功率出现了明显下降。     

Compton 散射对线偏光在相对论等离子体中调制不稳定性的影响

应用多光子非线性Compton 散射模型、电磁波非线性色散方程和Karpman 方法,研究了 Compton 散射对线偏光在相对论等离子体中调制不稳定性的影响,给出了等离子体的非线性色散、控制和调制不稳定性增 长率的修正方程,并进行了数值模拟。结果表明：与散射前相比,随无量纲化频率值减小,即趋于等离子体临界面处,散射使相同扰动波数引起的调制不稳定性增长率更大,使等离子体临界面处的调制不稳定性增长率较其余位置尤为显著。这是由于散射光使等离子体非线性增强,形成了激光场自聚焦和自成丝的缘故。