辐射烧蚀界面的单模Rayleigh-Taylor不稳定性分析

首先对惯性约束聚变(ICF)遇到的流体力学界面不稳定性作了简要的分析;其次讨论了Rayleigh-Taylor(RT)不稳定性在ICF中所起的作用;第三,根据一维数值计算结果,按照考虑密度梯度和烧蚀致稳的RT不稳定性增长的定标规律对不稳定性增长作了估计。最后在计算结果的讨论中,对有关实验测量提出某些倾向性的建议。     

Linear analysis of cyclotron-cherenkov and cherenkov instabilities in dielectric-loaded coaxial waveguides

We present, based on the cold fluid theory, linear analysis of the Cherenkov and cyclotron-Cherenkov instabilities which are driven when a linear electron beam is injected into a dielectric-loaded waveguide immersed in an axial magnetic field. In the analysis we consider azimuthally symmetric TM_0n modes. We derive dispersion relations for three types of waveguide, and compare computationally obtained linear growth rates of both instabilities. For the type A, which consists of a metallic cylinder with dielectric liner on its inner surface, the growth rate of the Cherenkov instability is larger than that of the cyclotron-Cherenkov instability. For the type B, which consists of a dielectric core and an outer metallic cylinder, both growth rates are comparable. And for the type C, which consists of a metallic core with dielectric liner on its surface and an outer metallic cylinder, the growth rate of the latter instability is higher than that of the former instability. Finally, for the type C, obtained are dependences of the oscillation frequency and the growth rates of both instabilities on the following parameters: the beam energy, the beam current, the axial magnetic field, the dielectric constant, and the thickness of the dielectric.     

The study of the weibel electromagnetic instability growth rate in the presence of the body stress

Body stress flow can be expected in the fast ignition imploding of the inertial fusion process that strongly damps small‐scale velocity structures. The Weibel instability is one of the plasma instabilities that require anisotropy in the distribution function. The body stress effect was neglected in the calculation of the Weibel instability growth rate. In this article, the propagation condition of impinging waves and the growing modes of the Weibel instability on the plasma density gradient of the fuel fusion with the body stress flow are investigated. Calculations show that the minimum value of the body stress rate threshold in the linear polarization is about 2.96 times greater than that of the circular polarization. Increasing 10 times of the density gradient and decreasing 2 times of the wavelength in the linear polarization and the circular polarization, respectively, lead to about 1.78 × 10⁶ times increment and 0.019 times decrement in the maximum of the Weibel instability growth rate. Also, the Weibel instability growth rate maximum in the circular polarization is about 10⁷ times greater than that of the linear polarization. The body stress flow and the density gradient tend to stabilize the Weibel instability in the circular polarization and act as a destabilizing source in the linear polarization. Therefore, by increasing steps of the density gradient plasma near the relativistic electron beam‐emitting region, in the circular polarization, the Weibel instability occurs at a higher stress flow.     

Influence of flow shear on localized Rayleigh–Taylor and resistive drift wave instabilities

The impact of velocity shear on the localized solutions of Rayleigh–Taylor (RT) and resistive drift wave (DW) instabilities has been investigated. Slab geometry is used, and the plasma density gradient is assumed to have a finite spatial structure. It demonstrates that the velocity shear has quite different effects on these instabilities: while it stabilizes RT instability and causes tilting of the eddies of equipotential contour, it has a very mild impact on the resistive DW instability and simply shifts the eddies with no tilting.     

非理想流体中Rayleigh-Taylor和Richtmyer-Meshkov不稳定性气泡速度研究

在随气泡顶端运动的坐标系中, 通过将理想流体模型推广到非理想流体的情况, 研究了流体黏性和表面张力对Rayleigh-Taylor (RT)和Richtmyer-Meshkov (RM)不稳定性气泡速度的影响. 首先得到了RT和RM不稳定性气泡运动的控制方程 (自洽的微分方程组); 其次给出了二维平面坐标和三维柱坐标中气泡速度的数值解和渐近解, 并定量分析了流体黏性和表面张力对RT和RM气泡速度和振幅的影响. 结果表明: 从线性阶段到非线性阶段的全过程中, 非理想流体中的气泡速度和振幅小于理想流体中的气泡速度和振幅. 也就是说, 流体黏性和表面张力对RT和RM不稳定性的发展都具有致稳作用. 关键词： Rayleigh-Taylor不稳定性 Richtmyer-Meshkov不稳定性 气泡速度 非理想流体     

Laser pulse modulation instabilities in partially stripped plasma

The laser pulse modulation instabilities in partially stripped plasma were discussed based on the phase and group velocities of the laser pulse and the two processes that modulation instabilities excited. The excitation condition and growth rate of the modulation instability were obtained. It was found that the positive chirp and competition between normal and abnormal dispersions play important roles in the modulation instability. In the partially stripped plasma, the increased positive chirp enhances the modulation instability, and the dispersion competition reduces it.     

Observation of beam instability in the SSRF storage ring

During the SSRF(Shanghai Synchrotron Radiation Facility) storage ring phase-I commissioning, some instabilities have been observed, and the broadband impedance has also been measured. The primary instabilities at present stage are vertical beam blow up and resistive wall instability.     

蒸发两层流系统的对流不稳定性分析

关于蒸发液层的Rayleigh-Marangoni-Benard不稳定性的研究中,早期文献中普遍采用的是单层流模型。近年来,一些学者采用两层流模型对蒸发稳定性进行了理论分析,有的文献中没有考虑蒸发率与饱和蒸汽压的耦合关系,所以得到的结果不能完全反应蒸发对系统稳定性的影响。本文建立了一种新的两层流模型,考虑了界面变形对系统稳定性的影响。采用线性稳定性方法对带有蒸发界面的两层流的Rayleigh-Marangoni-Benard对流不稳定性进行了分析,得到了临界 Marangoni数与波数的关系,重点讨论了蒸发系数以及重力对汽液两层流系统的不稳定性的影响。     

Observation of beam instability in the SSRF storage ring

During the SSRF(Shanghai Synchrotron Radiation Facility) storage ring phase-I commissioning, some instabilities have been observed, and the broadband impedance has also been measured. The primary instabilities at present stage are vertical beam blow up and resistive wall instability.     

Z箍缩等离子体不稳定性的数值研究

利用二维辐射磁流体程序模拟了钨丝阵Z箍缩等离子体腊肠不稳定性的演化：分析了存在不稳定性与没有不稳定性条件下等离子体内爆的差异；研究了不同初始密度扰动对x射线输出 功率和能量的影响.数值结果表明，在一定初始密度扰动范围内，这种不稳定性对x射线输 出的总能量影响不显著，但对x射线功率随时间变化的曲线有明显的影响.此外，还探讨了Z 箍缩等离子体数值模拟中低密度区的数值处理对数值结果的影响. 关键词： Z箍缩 腊肠不稳定性 数值模拟     

Instability Entanglement in the Electron Cyclotron Maser

Investigation of absolute instability (AI) and convective instability (CI) of the electron cyclotron maser has independently led to the birth of gyrotron oscillators and amplifiers. Here, it is demonstrated that these instabilities can form a cooperative relationship owing to the nonlinear behavior of the stimulated electron beam. The CI can be induced in a zero-drive system with the assistance of AI, and the ohmic losses of all the excited waves inside the system are greatly reduced, which is called “instability entanglement” here. According to the theoretical and experimental study of a 167/330 GHz gyrotron, when instability entanglement occurs, the ohmic dissipation decreases to one-ninth of the AI-only condition, and the output power is enhanced by 20%. This discovery is promising for surpassing the ceiling of output power and frequency of gyrodevices placed by ohmic losses.     

非对称核物质的化学不稳定性与力学不稳定性

基于扩展的Skyrme有效相互作用,在Hartree-Fock近似下对非对称核物质的化学不稳定性与力学不稳定性进行了研究,并与简单的三参数势,即所谓的软势与硬势的计算结果进行了比较.结果发现两种模型给出的非对称核物质化学不稳定性与力学不稳定性之间的关系是完全不同的.通过研究化学不稳定性在临界温度附近的行为发现,对软势与硬势,化学不稳定性可能出现在温度高于临界温度的气化(全爆炸)机制中.而对于SKM势参数,化学不稳定性不会出现在温度高于临界温度的气化(全爆炸)机制中.这种差别也反映在压强密度平面上力学不稳定 关键词： 非对称核物质状态方程 化学不稳定性 力学不稳定性     

PIC Simulation of Current‐Driven Buneman Instability in Presence of Collisional and Thermal Effects

Collisional and thermal effects on the nonlinear evolution of Buneman instability in an unmagnetized current‐driven plasma are investigated by particle in cell simulations. These simulations show that, as the time passes, the electron distribution function profiles deviate from initial shifted Maxwellian distribution and the electron phase‐space holes can be formed. The electron distribution function profiles also indicate the counter‐streaming and plateau formation. Moreover, the contour of the electric field and profiles of the growth rate display the resonance condition for this instability. Finally, the time evolution of the electric field energy density and ion kinetic energy in the presence of collisional and thermal effects are presented. These evolutions illustrate that in the presence of collisions, the growth rate of the Buneman instability is smaller than the collisionless case. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Increase of Kinetic Energy of Dusty Cluster Particles Due to Parametric Instability Caused by Nanosecond Electric Pulses

Experimental investigations of high voltage nanosecond pulses influence on charged dust particles in low pressure rf–plasma were carried out. Application of repetitive pulses leads to the vertical oscillations of the mi‐croparticles. Evolution of the total kinetic energy for the cluster consisting of 14 particles is investigated. Flat clusters exhibit parametric instabilities of horizontal modes. In the initial phase the kinetic energy oscillates around a certain value and its amplitude grows very slowly. At a certain moment during the instability it goes into the exponential growth phase and then saturates under the effect of repetitive pulses. It is possible if the eigenfrequency is the function of height and the dust particle oscillates vertically in the non uniform electric field (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

无碰撞等离子体中电子束流不稳定性的时空演化研究

应用二、三维相对论电磁粒子模拟程序研究双电子束流在无碰撞等离子体中传播引起的横向 电磁(Weibel类型)不稳定性和纵向静电不稳定性的发展演化过程.讨论了纯粹Weibel不稳定 性的发生和非线性饱和过程，观察到电流束合并、磁场重联等引起的电子横向加热现象.研 究了电流束传播方向激发的静电场对快电子束传播的影响，观察到其导致的束的横向调制、 磁场通道破坏现象.对这些过程的细致研究对更好的理解快点火物理中自生磁场的产生、快 电子输运等过程有重要意义.     

Self-patterned Si surfaces as templates for Ge islands ordering

We propose a two-step process, which is based on substrate nano-patterning by means of growth instabilities in a first step and self-assembling of Ge dots on the top of surface instabilities in a second step. We used the instabilities that develop during the growth of Si(Ge) layers on both nominal and vicinal Si (1 1 1) or (0 0 1) surfaces. Depending on the growth conditions (Ge concentration, growth temperature, thickness), various growth instability regimes were observed: pure kinetic regime, kinetically activated strain-induced regime and pure strain-driven regime. In the case of Si/Si growth, kinetic instabilities developed at different growth temperatures depending on the surface orientation. The critical exponents describing evolution with time have been determined: amplitude At^β and wavelength Lt^α. Experimental results show that each instability regime appears for a given growth temperature range that critically depends on the concentration of Ge. Evolution with time also depends on the Ge concentration. But in all cases, we evidence discrepancies between the experimental critical exponents and those predicted by classical modelling. We also give some examples of Ge dots self-organization on substrates nano-patterned (periodically undulated) by means of the different growth instabilities described above. In all cases, we observe Ge dots ordering along the substrate undulations due to step and/or strain effects. On kinetic instabilities (Si/Si(0 0 1) vicinal), Ge islands preferentially nucleate on step bunches. On SiGe(0 0 1) template layers, Ge dots nucleate on top of the SiGe undulations. In that case, strain gradients improved island ordering. The best ordering was achieved using SiGe(0 0 1) 10° off misoriented template layers as a result of almost perfect anisotropic morphology.     

Positively Biased Probes in Magnetized Plasmas

Positively biased probes in magnetized plasmas can create several phenomena which are not described by standard probe theories. These include transient currents for pulsed electrodes in the regime of Electron MHD, relaxation oscillations induced by large probes and high frequency instabilities at the sheath‐plasma frequency. Although they may limit the use of probes for diagnostic purposes they also offer new applications and belong to the general knowledge of probes in plasmas (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ion velocity shear-induced drift wave and momentum transport in non-Maxwellian magnetoplasma flows

We have investigated the diamagnetic flow in a non-uniform partially ionized plasma with non-Maxwellian electron population to explain the dynamics of ion velocity shear-induced low-frequency drift mode and associated instabilities. The dispersion relations are found, and instability threshold conditions are pointed out along with ion-parallel momentum transport due to drift motion with relative phase shift of fluctuating quantities in a non-conservative system. The real frequencies and instability growth rates are studied numerically and illustrated for typical space and laboratory plasmas. This study should be useful in understanding some aspects of low-frequency time-delayed perturbations with sheared flow leading to drift instabilities and cross-field parallel ion momentum transport in nonuniform magnetoplasmas containing a non-Maxwellian electron population.     

Filamentation Instability in a Current‐Carrying Plasma in the Presence of Quantum Effects

The filamentation instability of a current‐carrying plasma under the diffusion condition is investigated taking into account the Bohm potential and the Fermi electron pressure. Using quantum hydrodynamic equations, the dispersion relation and growth rate of the instability is obtained. It is found that the filamentation instability, in the presence of quantum effects, depends on various characteristic parameters such as: electron Fermi velocity, plasma number density, ion thermal velocity and electron drift velocity. Moreover, the wavelength region in which the instability occurs is more restricted and the minimum size of filaments is larger, in comparison with the classical case. It is also found that the growth rate of the instability is smaller in the presence of quantum effects. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cellular instabilities of expanding hydrogen/propane spherical flames at elevated pressures: theory and experiment

An experimental and theoretical investigation of the onset of cellular instabilities on spherically expanding flames in mixtures of hydrogen and propane in air at elevated pressures was conducted. Critical conditions for the onset of instability were measured and mapped out over a range of pressures and mixture compositions. An asymptotic theory of hydrodynamic and diffusional-thermal cell development on flames in mixtures comprised of two scarce fuels burning in air was also formulated. Predicted values of Peclet number, defined as the flame radius at the onset of instability normalized by the flame thickness, were shown to compare favorably with the experimentally measured values.