飞秒强激光与等离子体相互作用产生高能粒子的相关物理问题的理论和模拟研究
文献类型：学位论文
| 作者 | 王鑫 |
| 学位类别 | 博士 |
| 答辩日期 | 2010 |
| 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 | 激光尾波加速 有质动力 PIC 模拟 飞秒激光脉冲 瑞利长度，自聚焦 |
| 其他题名 | Theory and Simulation about Energetic Particles Generation via Relativistic Femtosecond Laser and Plasma Interaction |
| 中文摘要 | 高能量电子和离子束在医学治疗、各类成像诊断及惯性约束聚变快点火等方面有着极其广泛的应用前景。随着激光技术的迅速发展，特别是CPA技术的发明，人们已经能够获得峰值功率超过1022W/cm2，单个脉冲宽度小于10飞秒的相对论性强激光。这使得人们越来越重视激光与物质相互作用产生高能量带电粒子的研究。早在３０年前，Ｔajima等人提出了利用强度为1018W/cm2相应电场为108V/m的激光在稀薄等离子体中进行尾波加速的方案。在早期的理论研究，人们主要考虑在电子加速一维解析理论和计算机模拟。上世纪９０年代Pukhov等人通过二维粒子模拟、提出了空泡加速的概念。近几年，电子加速的高二维解析理论研究也开始受到重视。在离子加速方面，研究重点是靶后鞘层加速。此外，新的加速方案也不断提出。随着激光强度的提高，有质动力直接加速离子方案越来越受到推崇。在这些激光加速带电粒子的方案当中，得到能量高、单色性好、准直度佳的粒子是最终目的，为了达到这些要求，增加激光与等离子体相互作用距离和提高激光利用效率是其中几项重要的研究内容。 本论文主要进行了相对论性短脉冲激光与等离子体进行相互作用产生高能量带电粒子相关问题的研究。具体研究工作如下： １. 提出了超短超强激光在稀薄等离子体中激发尾波的二维解析模型。并在此基础上，研究了激光在不同背景等离子体中传播所激发的尾波过程，发现不同条件下尾波结构有显著差别，我们分析了相关的加速机制。相关结果与PIC模拟所显示的多维效应一致。这一解析模型为进一步地研究空泡加速打下基础。 ２. 利用包含移动窗口的PIC程序模拟了激光在稀薄等离子体中自引导传播、空泡激发并产生GeV量级高能电子的全过程。研究发现，通过选择合适的参数，可以使激光在等离子体空泡中实现自引导，其传播距离远远突破瑞利长度限制。在激光传播过程中，激光峰值功率基本不变，但由于能量的损耗使得激光脉宽减小，从而增大了电场梯度引起空泡尺度的增加。在此过程中，电子以自注入方式进入空泡中，在经过几个毫米的加速后达到GeV量级。 ３. 研究了多个超短超强激光脉冲对固体密度小靶进行连续加速的过程。通过对比模拟发现，在总能量相同、峰值功率不变情况下，把一个较长的激光脉冲分成两个较短的脉冲后，由于有质动力两次作用可以更有效地加速小靶。我们将四个激光脉冲连续作用一个小靶，得到100MeV量级的高能离子，并且其密度保持在临界密度以上。 ４. 近期伯克利等地的实验表明，将等离子体通道用于激光加速带电粒子的可以获得非常好的效果。作为通道中激光加速的前期理论研究，我们利用相对论及有质动力自聚焦解析理论分析了超短超强脉冲在中空等离子体通道中传播的过程，并与二维PIC模拟进行对照。研究表明激光在真空中自然散焦与等离子体通道边界的自聚焦效应相互竞争决定了激光的传播特性。我们研究了光斑在等离子体通道中反复震荡、并使激光保持高强度传播数个瑞利长度的全过程。我们还通过二维PIC程序模拟了弯曲通道对激光引导作用，探讨了此方法用于激光多级加速的可能性。 |
| 英文摘要 | Energetic electrons and ions have a very wide range of applications in the medical therapy, types of diagnostics and imaging for research and fast ignition in inertial confinement fusion. With the rapid development of laser technology, especially the invention of CPA technology, the laser with 1022W/cm2 scale peak intensity and less than ten femtosecond duration has been obtained. This has led to increasing emphasis on research about laser and matter interaction for generating charged particles. Thirty years ago, Tajima et al proposed the scenario of laser wakefield acceleraction in under-dense plasma, with the laser intensity about 1018W/cm2, and the electric field is 108V/m accordingly. Researchers were absorbed in one-dimensional analytical model and simulation on electron acceleration in the early decades. In the 1990s, Pukhov et. al began to simulate electron acceleration progress with two-dimensional program, and proposed the mechanics in bubble regime. Meanwhile, the high-dimensional electron acceleration theories are taken more and more attention these years. And in the field of ion acceleration, the most popular scheme is target normal sheath acceleration (TNSA). In addition, more and more ion acceleration schemes are presented. With the development of experimental technology and the laser intensity, the scheme of intense laser direct accelerate ions by the ponderomotive force is also being praised by everyone. In order to obtain monochromatic and collimated energetic particles, increasing the laser plasma interaction distance and the acceleration efficiency are two of the most important issues. This dissertation conducts relativistic ultra-short pulse laser and plasma interaction to generate energetic charged particles as well as related issues. Some studies are as follows: 1. We proposed an analytical model for intense laser interaction with under-dense plasma, and investigate the dependence of the wake structure on the laser parameter and the background plasma density. Many of the properties observed in the existing multidimensional particle-in-cell (PIC) simulations are qualitatively recovered. The model is simple but useful as the basis for further theoretical research. 2. Long-distance electron acceleration in laser-induced plasma wake bubble is studied by two-dimensional (2D) moving-window PIC simulation. It is shown that the intense laser pulse can be self-guided in the leading bubble for many Rayleigh lengths in appropriate conditions, with its spot size and peak intensity remaining almost unchanged. The flattening of the pulse front due to dissipation also ensures strong ponderomotive pressure on the plasma electrons, thus maintaining and even lengthening the bubble structure as the laser propagates. The electrons self-injected from the rear of the bubble can then be accelerated by the moving bubble potential well for a considerably longer distance. It is found that acceleration distance can be several millimeters and GeV electrons can be generated 3. Ion bunch acceleration through interaction of an ultra-short ultra-intense laser pulse and multiple short laser pulses with a small dense plasma pellet is studied using 2D PIC simulations. The contrastive simulations show that efficient ion bunch acceleration can be achieved with two laser pulses interacting with the target compared to an equally energetic single laser pulse, as the ponderomotive force acting on the target twice. Then we extend the study by for short laser pulse, and bunches of 100MeV level energetic ions are obtained. This density ion bunch has broad application prospects in many areas. 4. Analytical modeling and 2D PIC simulation are used to investigate the propagation of a short, relativistic laser pulse in a preformed plasma channel. Due to interaction with the channel-boundary plasma, the laser pulse can be guided over many Rayleigh lengths by the effect of ponderomotive force and self-focusing. The numerical simulation verifies the laser spotsize slightly oscillates while it is propagating, and also shows that the laser pulse can also be guided by a curved channel. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15627]  |
| 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 | 王鑫. 飞秒强激光与等离子体相互作用产生高能粒子的相关物理问题的理论和模拟研究[D]. 中国科学院上海光学精密机械研究所. 2010. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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