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题名	20TW皮秒激光加热等离子体产生快电子的若干特性研究
作者	张淼
学位类别	硕士
答辩日期	2005
授予单位	中国科学院上海光学精密机械研究所
导师	林尊琪
关键词	快点火 超短超强激光 快电子
其他题名	Characteristic Investigation of Fast Electrons Produced by 20TW Picosecond Laser-Plasma Interaction
中文摘要	激光惯性约束核聚变（ICF）的"快点火"方式自1994年提出以来，因为其放宽了对驱动压缩对称性和点火能量的要求迅速成为ICF研究的热点之一。但是由于开展时间短，"快点火"机制中的许多物理问题还需要仔细研究，其中快电子的产生问题就是一个复杂，但是对"快点火"机制至关重要的物理问题。在"快点火"机制中，当燃料的预压缩完成后，需要从外围注入一束超短超强激光并在临界面处产生大量定向性很好的快电子，快电子继续向高密度区传输并在高密度区一个很小的尺度范围（20微米左右）沉积能量形成点火热斑。论文首先分析传统ICF"中心点火"方式的过程和遇到的困难，以及"快点火"机制涉及的物理问题，提出了论文研究的具体内容。介绍了超短超强激光与等离子体作用产生快电子的理论和实验研究进展。基于真空中单电子运动模型，编制程序数值计算得到了横向强度也呈高斯分布的激光脉冲与初始静止的电子的相互作用结果。不同激光参量条件下，得到了电子的能量增益与激光强度、焦斑大小和脉冲宽度关系。高斯激光脉冲焦斑较大时，电子没有明显的能量增益，高斯激光脉冲焦斑太小时，电子也没有明显的能量增益。电子的能量增益有一个最佳焦斑大小。激光脉冲宽度一定时，最佳焦斑大小随激光强度的增大而增大。在相同激光强度下，电子能量增益的最佳焦斑大小随脉冲宽度的增大而增大，但最佳焦斑大小与脉冲宽度的比值是不变的。在20TW皮秒激光器上完成了激光－A1薄膜靶相互作用过程中产生的快电子的角分布和能谱的测量。实验得到：激光功率密度由非相对论到相对论强度增加时，靶后表面快电子的主发射力向由沿靶面法线方向改变为沿激光传播力向；激光功率密度在非相对论强度，靶后表面法线方向快电子能谱拟和平均温度符合共振吸收温度定标率；激光功率密度达相对论以上，靶后表面法线方向快电子能谱拟和平均温度高于已有的温度定标率。
英文摘要	The fast ignition concept of inertial confinement fusion (ICF) advanced by Tabak et aim 1994 ,because the driver energy scales could be reduced and the irradiation symmetry requirements could be eased,has attracted the attention of many researchers.The fast ignition studies have been conducted just for several years and many physical questions need to be resolved.The fast electron generation studies,one of the many questions,are complex but essential for fast ignition concept. In the fast ignition concept,the fuel,after precompression,is ignited by fast electrons,produced in the high-intensity laser-plasma interaction,which then propagate from critical density to the high-density core(about 20 jum distance). This paper first discuss and compare the gain model that describes the conventional approach to inertial fusion with the model of fast ignition,and then introduce the progress about the theoretical and experimental study of the fast electrons produced by intense laser-plasma interaction. The main works results of this paper are shown as follows: Electron acceleration from the interaction of an Gaussian laser pulse with initial stational electron is investigated,using a single test electron model in vacuum.The electron energy gain have a optimum focal spot size.There are no evident energy gain when the focal spot is too big or small.We find that the electron retained energy depends not only on the laser intensity,focal spot size,but also on the pulse length.The optimum focal spot size increases with laser intensity and pulse length.But the ratio of the optimum focal spot size to pulse length is fixed when given laser intensity. The characteristics of the forward hot electrons produced by 20TW p-polarized picosecond laser-plasma interactions are studied at laser intensities from subrelativistic to relativistic. The spatial distribution of forward hot electrons was measured by LiF thermoluminescence dosimeters.An electron spectrometer with 2000 Gass permanent magnets was used to measure the electron energy distribution.The peak of the hot electron beam shifts to the laser propagation direction from the target normal direction as the laser intensity reaches the relativistic. The temperature of hot electrons are fitting resonance absorption scaling law as the laser intensity under the relativistic.The temperature of hot electrons are much higher than that expected by the empirical scaling law as as the laser intensity reaches the relativistic.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/16525]
专题	上海光学精密机械研究所_学位论文
推荐引用方式 GB/T 7714	张淼. 20TW皮秒激光加热等离子体产生快电子的若干特性研究[D]. 中国科学院上海光学精密机械研究所. 2005.

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