超短超强激光脉冲与固体密度等离子体相互作用的理论和粒子模拟研究
文献类型：学位论文
| 作者 | 栾仕霞 |
| 学位类别 | 博士 |
| 答辩日期 | 2012 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 余玮 |
| 关键词 | 模式转换，u×B电子振荡，低频电子振荡，后孤子，电磁能量捕获 |
| 其他题名 | Theoretical and particle simulation research on the interaction of ultra-short ultra-intense laser pulses and solid-density plasmas |
| 中文摘要 | 啁啾脉冲放大技术的发展，使激光与等离子体相互作用成为一个非常重要的研究领域，有着广泛的应用前景。尤其是惯性约束聚变中“快点火”技术的提出，涉及丰富的激光与等离子体相互作用的过程。“快点火”概念的第一阶段是激光在等离子体中传播的过程中，部分电子被强激光有质动力加速到兆电子伏（ ）以上。电子束的产生、加速，以及在低密度等离子体中的传输是第一阶段的关键物理问题。第二阶段是强激光在被压缩成高密度的稠密等离子体中打洞时，相对论电子束开始脱离激光并在高密度等离子体中输运，并在芯区边缘沉积能量形成点火热斑的过程。可见，激光与固体靶等离子体相互作用是“快点火”研究的重要内容。因此本论文将围绕激光在固体密度等离子体中的传输、能量吸收机制，以及等离子体电子和离子的时间演化等物理问题，进行理论和数值模拟研究，主要内容包括： 1. 研究了超短超强激光与固体密度等离子体相互作用的稳态情形。超短超强激光辐照固体靶，因为相互作用时间短，可以形成很强的电荷分离场，这是超短超强激光脉冲与固体密度等离子体相互作用的重要特征；研究了模式转换效应产生的激光频率的静电振荡以及 加热产生的两倍激光频率的电子振荡。研究发现，很强的静电分离场能够有效的增强 振荡，这一点与一项最新的研究相符。 2. 研究了超短超强线偏振激光脉冲与固体密度等离子体相互作用的时间演化过程。首先我们剖析了高密度等离子体峰的产生过程以及向前运动的情况；并重点研究了激光脉冲从靶面的反射以及所经历的多普勒频移；最后研究了线偏振光与固体靶相互作用中出现的 高频电子振荡和作用后的低频受迫电子振荡。 3. 利用强激光脉冲与固体靶相互作用的二维时间演化模型详细研究了圆偏振激光与固体靶相互作用后的低频电子振荡的产生机制。圆偏振比线偏振的情况下形成的低频电子振荡要强得多。 4. 研究了强激光与近邻界密度等离子体相互作用过程中后孤子的形成与演化。重点着眼于后孤子的形成过程；研究了后孤子的半周期的驻波场结构特征以及演化过程；PIC数值模拟研究了相同参数的后孤子的形成和演化，与理论模型得到的结果一致，证明了理论模型的有效性；最后利用PIC数值模拟研究了捕获在预设空腔中的多峰电磁结构。 |
| 英文摘要 | In recent years, the development of Chirped Pulse Amplification technique makes laser-matter interaction one of the most important areas in physics science, which has much potential applications. Especially, the study of the interaction of ultrashort intense laser pulses with plasmas, which is motivated primarily by the fast ignition scheme of inertial confinement fusion, has received more and more attention. In the first stage of fast ignition scheme, electrons are generated due to the ponderomotive force of the intense laser pulse. The generation and acceleration of the electron bunch, and the transportation in the underdense plasmas, are the key issues in this stage. In the second stage, the relativistic electron bunches cast off from the laser pulse and transport in the dense plasmas during the hole boring of the intense laser pulse. The deposit of the electron energy in the edge of the target core forms the hot-spot ignition. In view of this, laser-solid interaction is important for fast ignition scheme. This thesis is devoted to theoretical and numerical studies of the interaction of relativistic laser and solid state target and near-critical plasmas, including the mechanism of propagation and absorption of laser pulse, the transportation of electrons and ions, etc. Specific results are given as follows: 1. A simple but comprehensive two-dimensional analytical model for the interaction of a normally incident short intense laser pulse with a solid-density plasma is proposed. Electron cavitation near the target surface by the laser ponderomotive force induces a strong local electrostatic charge-separation field. The cavitation makes possible mode conversion of the laser light into longitudinal electron oscillation at laser frequency, even for initial normal incidence of laser pulse. The mode conversion occurs at the periphery of the laser spot, where laser-plasma interaction is relatively weak. So the electron oscillation at laser frequency is weak. The intense charge-separation field in the cavity can significantly enhance the laser induced electron oscillation at twice laser frequency to density levels even higher than that of the initial target. 2. A two-dimensional theoretical model for the evolution of solid-density plasma irradiated by short, intense laser pulse is introduced. The ion motion effect is taken into account. The electrons near the target surface are pushed inward by the radiation pressure, leading to a receding electron density jump where laser is reflected. The laser pulse reflected from the receding electron density jump loses energy in plasma and suffers Doppler frequency red-shift, which can provide valuable information on the laser absorption rate and the speed of the receding electrons. Electron oscillations, including the oscillations across the density jump at twice laser frequency during the laser action, as well as the low-frequency oscillations appearing after laser action, are identified for linearly polarized laser pulse and solid target interaction. 3. The generation mechanism for low-frequency oscillations appearing after circularly polarized laser action is studied in detail using the model for the evolution of solid-density plasma irradiated by short, intense laser pulse. It is stronger than that for linearly polarized laser pulse. 4. The formation and evolution of laser-induced postsoliton in near critical density plasma are studied using two-dimensional (2D) theoretical model and PIC simulation. We focus on the generation process of the postsoliton. A considerable part of laser energy can penetrate plasma, and then be trapped in an empty cavity bounded by overdense plasma peaks. The self-trapped electromagnetic fields remain as a half-cycle standing wave, with the amplitude peaking at the cavity center and vanishing at the boundary. As the cavity expands slowly, the field amplitude decreases and oscillation frequency reduces to merely a small faction of laser frequency. The PIC simulations verify the valid of the theoretical model. The trapping of the electromagnetic energy in the preformed plasma cavity is studied using PIC simulations. The trapped laser preformed plasma cavity is a axisymmetric multi-peak structure, which can keep for hundreds of laser periods in the cavity. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15722]  |
| 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 | 栾仕霞. 超短超强激光脉冲与固体密度等离子体相互作用的理论和粒子模拟研究[D]. 中国科学院上海光学精密机械研究所. 2012. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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