On the Rayleigh-Taylor Instability for Two Uniform Viscous Incompressible Flows

The authors study the Rayleigh-Taylor instability for two incompressible immis- cible fluids with or without surface tension, evolving with a free interface in the presence of a uniform gravitational field in Eulerian coordinates. To deal with the free surface, instead of using the transformation to Lagrangian coordinates, the perturbed equations in Eule- rian coordinates are transformed to an integral form and the two-fluid flow is formulated as a single-fluid flow in a fixed domain, thus offering an alternative approach to deal with the jump conditions at the free interface. First, the linearized problem around the steady state which describes a denser immiscible fluid lying above a light one with a free interface separating the two fluids, both fluids being in （unstable） equilibrium is analyzed. By a general method of studying a family of modes, the smooth （when restricted to each fluid domain） solutions to the linearized problem that grow exponentially fast in time in Sobolev spaces are constructed, thus leading to a global instability result for the linearized problem. Then, by using these pathological solutions, the global instability for the corresponding nonlinear problem in an appropriate sense is demonstrated.     

平面应变条件下孔洞化不稳定性问题研究

考虑平面应变条件下，由一类推广的幂次neo—Hookean材料组成的内部分布温度场的圆柱体在轴向和径向载荷作用下的孔洞化不稳定性问题，研究中发现当材料参数满足一定的条件时，存在着一个载荷临界值，当外加载荷大于该临界值时，圆柱体中心将出现一个圆柱形的孔洞，即发生了孔洞化不稳定性现象并详细讨论了温度和材料参数对孔洞化极限载荷的影响。     

“神光”Ⅱ装置激光烧蚀驱动侧照明R-T不稳定性实验探索

R-T(Rayleigh-Taylor)不稳定性实验研究对于天体物理和ICF都有重要的意义。特别是侧向照明的诊断方案，物理上很直观实验上也相对容易实现因此受到各国的重视。2003年在“神光”Ⅱ开展了一轮打靶实验。     

反馈抑制HLS注入过程中β振荡的尝试

为了提高注入束流的积累,抑制由于注入系统误差所引起较大的β残余振荡是非常有必要的.本文较系统地介绍了合肥光源(HLS)抑制注入β振荡反馈系统的设计思想、原理和线路,并提供了它的初步实验结果.作为原理论证和预研,我们使用了一个相对简单的模拟滤波器和移相器对Kicker过程激发的β振荡进行反馈,看到了明显的抑制作用.为以后研制低频和高频反馈系统,研究抑制束流的横向和纵向不稳定性打下基础.     

Electromagnetic Instabilities Excited by Electron Temperature Anisotropy

One-dimensional particle-in-cell simulations are performed to investigate the nonlinear evolution of electromagnetic instabilities excited by the electron temperature anisotropy in homogeneous plasmas with different parameters. The results show that the electron temperature anisotropy can excite the two right-hand electromagnetic instabilities, one has the frequency higher than Ωe, the other is the whistler instability with larger amplitude, and its frequency is below Ωe. Their dispersion relations are consistent with the prediction from the cold plasma theory. In the initial growth stage (prediction from linear theory), the frequency of the dominant mode (the mode whose amplitude is large enough) of the whistler wave almost does not change, but in the saturation stage the situation is different. In the case that the ratio of electron plasma frequency to cyclotron frequency is larger than 1, the frequency of the dominant mode of the whistler wave driRs from high to low continuously. However, for the case of the ratio smaller than 1, besides the original dominant mode of the whistler wave whose frequency is about 2.6ωe, another dominant mode whose frequency is about 1.55ωe also begins to be excited at definite time, and its amplitude increases with time until it exceeds the original dominant mode.     

自由表面射流磁流体不稳定性分析(I)

利用微分解析方法分析了自由表面液态金属射流在非均匀的横向磁场中的稳定性行为，得出了在给定射流初始速度分布和磁场分布条件下，射流的速度空间分布表达式。在特定的条件下，射流存在固有稳定区，其稳定区长度与横向磁场的空间非均匀程度和射流的初始速度有关；但其向外溅射的位置与BT横向磁场的非均匀程度、射流的初始速度、液态金属粘滞系数和重力加速度有关。     

直接驱动柱内爆流体力学不稳定性数值模拟

 给出了LARED-S程序对直接驱动柱内爆流体力学不稳定性模拟的物理方程，介绍了一种直接驱动柱内爆靶的结构，给出了模拟中使用活动网格追踪和其他一些需要注意的问题。对OMEGA激光器直接驱动柱内爆实验物理模型进行了简化处理：使用理想气体状态方程，假设烧蚀层、标识层和内部填充材料为同一介质，只在密度上有差别；采用全电离和单温近似，在内爆过程中仅考虑热传导过程而忽略辐射和非局域电子热传导等过程的影响。模拟结果表明：LARED-S程序与LASNEX程序的计算结果基本上符合。     

合肥光源储存环上八极磁铁的动力学效应分析

 为达到合肥光源二期工程通用模式的设计流强，在储存环上选择垂直方向β函数比较大的位置增加一组八极磁铁。该组八极磁铁对水平方向动力学孔径影响很小，虽然垂直方向动力学孔径明显减小，但仍然大于物理孔径，不会影响束流的注入积累过程。该组八极磁铁产生的垂直方向振荡频率分散可以提供ms量级的Landau阻尼时间，将明显增强抑制垂直方向束流集体不稳定性的能力。该组八极磁铁投入运行后，合肥光源注入积累过程明显改善，注入流强从无八极磁铁时的约100 mA提高到330 mA左右。     

热电子等离子体的低频交换不稳定性

本文用磁流体理论,导出了包含导电端板“线结”效应的热电子等离子体低频交换模的色散关系,分析了热电子环的稳定作用,求出了稳定性判据。“线结”效应能大大降低交换模的增长率。取热电子密度为零,就得到简单流体等离子体的结果。