靶结构对烧蚀模式激光推进效应影响的数值模拟

 强激光辐照于固体平面靶产生高温、高压等离子体喷射,进而对固体靶产生力学推进效应,这是烧蚀模式激光推进的基本原理。采用针对高温气体（等离子体）电离度的一种近似计算方法,以及具有五阶精度的广义Godunov差分格式-加权本质无振荡格式WENO（Weighted Essentially Non-Oscillatory Schemes）,对强激光烧蚀固体靶产生等离子体喷射推进效应进行数值模拟。计算了固体靶面横向尺寸与激光光斑大小对推进效应影响的耦合关系,以及不同靶面结构烧蚀压力随时间的变化及其推进效应参数变化。数值模拟结果表明,靶面横向尺寸与光斑大小具有最优耦合值;固体靶面增加约束喷管结构对激光推进效应明显增大,并且随着约束喷管位置的不同,对激光推进效应增大的影响也有较大差异。     

靶与光斑尺寸对激光冲量影响的数值模拟

采用二维雷诺平均N-S方程,数值模拟研究了大气条件下短脉冲激光与固体靶相互作用所产生等离子体的动力学过程。采用k-ε两方程模型用于湍流的数值模拟,分别利用ROE格式和二阶中心格式对对流通量和粘性通量进行离散处理;用高斯-赛德尔隐式格式对方程进行时间推进求解。数值模拟给出了激光引发靶蒸气等离子体侧向膨胀、稀疏等二维流体动力学过程的物理图像,讨论了靶与光斑尺寸对脉冲激光冲量的影响。结果表明,不同宽度固体靶受到的激光冲量有很大差异,固体靶宽度越大,受到的激光冲量也越大。     

由强激光产生的烧蚀等离子体随时间演化的数值模拟

采用单流体模型描述由强激光产生的烧蚀等离子体,并用具有五阶精度的广义Godunov差分格式——加权本质无振荡格式对该模型进行离散化,考虑激光与等离子体相互作用和能量耦合,数值模拟强激光与固体靶相互作用时产生的烧蚀等离子体随时间演化的物理过程,给出数值模拟结果,并对其进行分析和讨论.数值模拟结果表明,激光能量在靶面等离子体中被强烈吸收,激光支持LSD(Laser Supported Detonation)波速度约为理想LSD波速度的一半.     

激光与固体靶面烧蚀等离子体的能量耦合计算

 强激光辐照下固体靶表面迅速汽化产生靶蒸气等离子体,激光穿过等离子体区到达固体靶表面的过程就是激光束与等离子体的能量耦合与交换过程。采用具有五阶精度的WENO差分格式和简易等离子体状态方程模型对激光与等离子体相互作用的复杂物理过程进行了数值计算,分析了激光束能量在等离子体区中的吸收、屏蔽效应等动态耦合规律以及激光支持等离子体前驱冲击波传播。数值模拟结果表明：激光能量是支持靶面等离子体运动的唯一原因,能量屏蔽效应对激光与等离子体能量耦合有很大影响,通过控制激光脉冲宽度,可以合理调节屏蔽效应的影响。     

线极化强激光与轻元素气体相互作用产生的电子剩余能

 对线极化超短脉冲强场电离进行了回顾和分析。对不同参数的超短脉冲、线极化强激光与轻元素气体靶相互作用产生的等离子体中电子剩余能进行了解析和粒子模拟(CIC)数值计算。考虑到强场线极化光产生的等离子体的高电离度和低电子温度的特点,采用了有别于通常计算逆轫致吸收的方法,用零温度近似计算逆轫致效应。CIC模拟计算强场与物质相互作用物理过程中还考虑了纵向电场效应。给出了强场线极化光与氦和氖元素气态靶相互作用的理论计算结果和相应的结论。     

激光等离子体动量转换效率的实验研究

强激光与固体靶相互作用时，产生的高速喷射的等离子体对靶具有强烈的反冲作用，因此，激光等离子体可以作为一种新型的推进动力源.与传统的化学燃料推动相比，激光等离子体具有较高的比冲和有效载荷比等特点.对纳秒激光脉冲与铝、石墨、铅和碳氢靶相互作用时，等离子体对靶的冲量进行了实验测量，研究了大气与真空环境下的靶动量与激光聚焦面积的关系，并对部分实验结果与理论计算的数值进行了比较.实验结果显示，大气与真空环境下的靶动量有很大的差异，并且真空下的靶动量受材料性质的影响较大，与以往长脉冲激光的实验结果有很大的不同. 关键词： 激光等离子体 动量 动量耦合系数     

薄铝埋点等离子体K线光谱半定量实验测量

 提出了一种薄埋点靶：直径为200 mm、厚度为0.1 mm的铝点埋在20 mm厚的CH膜底衬中，表面再覆盖0.1 mm厚的CH膜。在星光Ⅱ激光装置上利用束匀滑激光打该埋点靶，在靶前向采用胶片记录的晶体谱仪测量铝离子K线谱，获得了铝离子K线谱半定量实验结果。并开展了非平衡铝等离子体发射光谱的理论计算分析。研究结果表明：采用单一等离子体状态且不考虑自吸收效应模拟计算获得的理论谱与实验谱符合较好，通过激光打薄埋点靶能够产生均匀的用于研究离化动力学和原子结构计算理论的光性薄高温等离子体。     

填充预等离子体通道靶激光电子加速研究北大核心CSCD

采用紧聚焦的超强短脉冲激光与固体通道靶相互作用是获得大电量、高准直相对论电子束的一种有效方式。实验中由于激光预脉冲烧蚀靶壁产生预等离子体会膨胀、填充到真空通道中,从而导致电子束品质发生变化。采用二维PIC粒子模拟程序研究了通道靶中填充预等离子体的电子加速过程。模拟结果显示,在功率密度为5.0×10^(20W/cm^(2))的超强短脉冲激光条件下,通道中填充一定密度的等离子体时激光场优先与低密度等离子体相互作用,激光脉冲与通道壁的相互作用减弱,电子加速机制由纵向场主导的真空电子加速转变为横向电场主导的等离子体电子加速,产生电子束具有更大的电荷量,但能量降低,发散角增大。     

时间相关外场中量子系统时间演化的辛格式

对显含时间的可分线性哈密顿系统构造了2阶模方守恒-辛格式和显式辛格式,并计算了1维有限宽无限深势阱中的电子与模拟激光场的相互作用,结果与理论分析一致。为数值研究时间相关外场中的量子系统,特别是强激光与原子相互作用提供了合理和有效的方法。     

二维三温能量方程的差分格式及平面靶数值模拟

通过统一二维直角坐标与柱坐标下三温能量方程的差分格式,实现了LARED-H(laser radiationelectron dynamic holehurm)程序既可以模拟正入射激光平面靶过程,也可模拟斜入射平面靶问题,从而扩展了LARED-H程序的功能.使用发展后的LARED-H程序进行了直角坐标系下线聚焦打靶耦合过程数值模拟,给出了不同入射角度下靶等离子体的膨胀过程.     

Controlled wake field acceleration via laser pulse shaping

We consider the interaction of high-intensity laser pulses with underdense plasmas and address the problem of the excitation of strong and stable wake plasma waves with regular electric fields to provide effective acceleration of charged particles over appreciably long distances. It is known that a relativistically strong laser pulse longer than the wavelength of plasma waves, propagating in a plasma is subject to self-modulation. This may result in a nonstationary behavior of the produced plasma wake field/particle dephasing, and reduced net acceleration. In this paper we present the results of 1(2/2)-D and 2(1/2)-D particle in cell (PIC) simulations which demonstrate that regular wake electric fields may be obtained by a properly shaped laser pulse (sharp steepening of its leading front). These results are relevant to the design of the 100 MeV laser wake field electron acceleration experiment that uses a terawatt picosecond CO₂ laser and is under construction at the Brookhaven Accelerator Test Facility     

Theoretical analysis and numerical simulation of the impulse delivering from laser-produced plasma to solid target

A plasma is produced in air by using a high-intensity Q-switch Nd：YAG pulsed laser to irradiate a solid target, and the impulses delivering from the plasma to the target are measured at different laser power densities. Analysing the formation process of laser plasma and the laser supported detonation wave （LSDW） and using fluid mechanics theory and Pirri＇s methods, an approximately theoretical solution of the impulse delivering from the plasma to the target under our experimental condition is found. Furthermore, according to the formation time of plasma and the variation of pressure in plasma in a non-equilibrium state, a physical model of the interaction between the pulse laser and the solid target is developed. The plasma evolutions with time during and after the laser pulse irradiating the target are simulated numerically by using a three-dimensional difference scheme. And the numerical solutions of the impulse delivering from the plasma to the target are obtained. A comparison among the theoretical, numerical and experimental results and their analyses are performed. The experimental results are explained reasonably. The consistency between numerical results and experimental results implies that the numerical calculation model used in this paper can well describe the mechanical action of the laser on the target.     

8 mm微波反射成像系统准光结构

微波反射成像（MIR）是等离子体湍流扰动诊断中的一种重要手段，它注重于测量高时空分辨力的二维/三维分布，实现等离子体空间湍流结构的可视化实时观测，以获得更为准确的物理信息。针对等离子体诊断要求，结合托卡马克HL-2A装置的参数,对具有准光结构的8 mm微波反射成像系统进行了理论计算和仿真设计，设计出一套准光系统，为指导微波反射成像的系统设计奠定基础。     

Modeling the triggering of streamers in air by ultrashort laserpulses

The physical processes involved in the triggering of ionization waves (streamers) by ultrashort laser pulses, focused in air at 350 Torr and in a uniform electric field, are investigated by means of a one-dimensional (1-D) numerical model. The model describes the interaction of the laser pulse with air and takes into account many of the reactions in the laser-created plasma as well as the radial expansion of the plasma. Consequences of the model are that the threshold electric field for the appearance of streamers is an increasing function of the delay between the laser pulse and the electric field pulse and a decreasing function of the laser energy. Also, it appears that the electron temperature, the plasma density and radius, and the conduction of heat across the plasma boundaries play major roles in the capacity of the laser-created plasma to trigger streamers. The results of the model are compared with the available experimental data     

数值研究二维含时薛定谔方程

采用二维渐近边界条件,将任意极化激光与原子相互作用的二维含时Schr(o)dinger方程无穷空间初值问题转化为有界空间的初边值问题,近而将截断后的初边值问题离散成线性正则方程组,而后利用辛算法求解正则方程得到含时波函数.最后利用含时波函数求得高次谐波谱,证明二维渐近边界条件和辛算法是合理而有效的.     

强激光辐照铝靶的辐射流体动力学模型及数值求解

本文改进了传统的辐射流体动力学模型,建立了完整的一维单流体双温度辐射流体力学方程组描述5×10⁸w/cm²高斯脉冲激光与一维半无界铝靶在真空中耦合所产生的靶外等离子体的发展过程,并建立了相应的数值模拟模型,计算结果与有关文献和实验比较,取得了定性与定量的一致.     

Two-dimensional fluid model simulation of bell jar top inductivelycoupled plasma

In the present paper, argon (Ar) plasmas in a bell jar inductively coupled plasma (ICP) source are systematically studied over pressures from 5 to 20 mtorr and power inputs from 0.2 to 0.5 kW. In this study, both a two-dimensional (2-D) fluid model simulation and global model calculation are compared. The 2-D fluid model simulation with a self-consistent power deposition is developed to describe the Ar plasma behaviour as well as predict the plasma parameter distributions. Finally, a quantitative comparison between the global model and the fluid model is made to test their validity