激光等离子体冕区不稳定性控制研究
文献类型：学位论文
| 作者 | 吴衍青 |
| 学位类别 | 博士 |
| 答辩日期 | 2000 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 韩申生 |
| 关键词 | 强激光 等离子体 不稳定性 时频分布 |
| 中文摘要 | 强激光与等离子体非线性相互作用研究中，各种不稳定性过程的研究在ICF、等离子体加速器以及天体物理等领域都是很重要的。我们的工作主要涉及参量不稳定性的控制、制备大尺度等离子体时影响其均匀性的辐射冷却不稳定性以及数值模拟结果诊断方法这几个方面，取得了如下主要研究成果：1.首次提出了用CPA技术产生宽带调频（UBFM）激光脉冲控制参量不稳定性的方法。近年来超短超强激光技术的飞速发展，使我们可以探索激光等离子体相互作用的更多的新领域。但是，在强场激光物理领域内人们的注意力仍主要集中在如何获得更短更强的超短脉冲激光上，对飞秒脉冲所具有的超宽光谱（或超短相干时间）则没有引起足够的重视。我们发现在非均匀等离子体中，根据参量不稳定性的性质，可以通过适当调节超宽频谱调频（UBFM）激光脉冲的参数，增强或减弱不稳定性的发展。UBFM激光脉冲不仅为我们提供了选择性激发指定的不稳定性的可能，而且还提供了影响能量沉积和超热电子性质（如温度、方向性）的新途径。2. 在对超短超强激光与等离子体相互作用进行模拟时，有关各种波模的诊断量往往是时间上和空间上的非平稳信号。通过了解不同时刻（或空间位置）信号的谱分布，我们可以获得更多的信息。我们将近年来迅速发展的时频分布技术应用于超短超强激光与等离子体相互作用的PIC模拟结果的诊断。通过实例清楚地看出，用时频分布技术等现代信号处理技术诊断模拟结果中的非平稳信号具有重要意义。时频分布等现代信号处理技术可以成为PIC模拟结果诊断的强有力工具。3. 线状激光等离子体作为在中小激光器上获得大尺度等离子体的手段，广泛应用于与ICF相关的激光等离子体非线性相互作用研究中。线聚焦激光等离子体还被广泛地用作X射线激光的增益介质。我们定量分析经线状等离子体中RCI和X射线辐射非均匀性之间的关系，并且得出结论，RCI是解释当泵浦激光停止以后线状等离子体非均匀性发展的一个可有机制。所以使用低Z靶及减少光源所造成的长波长扰动将可以减少RCI的影响。另外，超热电子的产生和输运在传统的ICF方案和“快点火”方案中都是很重要的问题。我们还研究了低密度等离了体中由参量不稳定性产生的超热电子及其输运。我们通过研究指出，弱碰撞项的加入影响了碰撞吸收，提高了热电子温度，静电波破裂时的场能下降。这些改变了超热电子的总能量和分布；电子-离子碰撞的存在还增强了自洽电场，阻碍了超热电子的输运，同样也是限制超热电子能量的重要因素。 |
| 英文摘要 | In the study of Laser plasma nonlinear interaction, various instabilities attract much intention, which are essential to the fields of laser-fusion, plasma accelerators and astrophysics. We are mainly concerned about the control of parametric instabilities, radiative cooling instability in lasrgr-scale laser produced plasma and the diagnostic tools of numerical simulation. The main results we have obtained are as follows. 1. We considered the idea of controlling the parametric instabilities (suppression and selected enhancement) and observed selected stimulation parametric instabilities in numerical simulation. We showed that parametric instabilities can be controlled with ultrabroad bandwidth frequency modulated(UBFM) laser pulse. The progress in the development of ultra-intense, ultra-short pulse lasers has allowed for the exploration of many new regimes in the field of laser plasma interaction. But, in contrast to the rapidly growing interests in ultra-intense laser plasma interaction and its applications, few attention has been concentrated on the ultrabroad bandwidth associated with these ultra-short laser pulses. We show that, according to the properties of parametric instability, one can either enhance or reduce the intensity of the instability by a UBFM laser with properly selected pumping parameters. the routine generation of UBFM laser pulse has already provided us not only the possibility of selectively maximizing or minimizing a specific instability but also the new possibilities of influencing the location of energy deposition and the properties of suprathermal electrons such as temperature, directionality and efficiency for various applications. 2. In the simulation of interaction between plasma and ultra-intense, ultra-short laser pulse, the signal about various wave modes we get from simulation is usually non-stationary in time and space. More information can be obtained if the time(or space) spectrum distribution of the signal is known. We use some tools of time-frequency distribution to diagnose the results from PIC simulation and conclude that modern signal processing tools is powerful to diagnose the results from simulation. 3. RCI should be treated seriously in the study of inertial confinement fusion (ICF) because line-shaped laser plasma is widely adopted to investigate the non-linear laser-matter interaction process relavant to ICF. Line-shaped laser plasma also widely adopted as gain medium of X-ray laser. We have quantitatively analyzed the relationship between RCI and X-ray emission nonuniformity and conclude that RCI is a possible mechanism that explain the nonuniformity evolution of line-shaped laser plasma during the laser heating as well as after the pumping laser has been turned off. Additionaly, the producation and transportation of suprathermal electrons are important in both tranditional and "Fast Ignition" ICF schemes. We studied the suprathermal electrons come from parametric instabilities. The work shows that the collisional damping rate increases by adding the weak electron-ion collisional term. So the temprature of hot electrons and the wavebreaking amplitude of electrostatic field decreases. The energy and distribution of the suprathermal electrons changes by the factors above. Also the weak electron-ion collision enhences the self-consistant field which resists the transportation of suprathermal electrons. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15385]  |
| 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 | 吴衍青. 激光等离子体冕区不稳定性控制研究[D]. 中国科学院上海光学精密机械研究所. 2000. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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