超强超短激光驱动的尾波场级联电子加速的理论和实验研究
文献类型：学位论文
| 作者 | 陈强 |
| 学位类别 | 硕士 |
| 答辩日期 | 2013 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 刘建胜 |
| 关键词 | 激光尾波场加速 超强超短激光 相位控制 隧穿电离注入 betatron振荡。 |
| 其他题名 | Investigations of Cascaded Laser Wakefield Acceleration Driven by Ultra-short Ultra-intense Laser Pulses |
| 中文摘要 | 激光尾波场加速器能够提供相比于传统射频加速器高3个量级的加速梯度，是台式化自由电子激光器的理想电子源。单级的激光尾波场加速器能够获得GeV量级的准单能电子束，但是电子束的能散度往往不够小而且不易控制。这是由于电子的注入和加速无法独立控制，而且这两者对激光及等离子体的要求是不同的。激光尾波场级联加速方案能够分别独立控制电子注入和电子加速两个过程，因而能够获得低能散度的数GeV能量的准单能电子束。为了获得稳定的高性能电子束，需要优化激光驱动级联尾波场电子加速器的注入级和加速级的匹配。本论文围绕激光尾波场级联加速方案展开了相关的实验研究，并在理论和particle-in-cell (PIC)的基础上对隧穿电离注入机制进行了唯象的分析，取得了以下方面的进展： 1. 参与搭建了相对论性强激光驱动激光尾波场级联电子加速实验研究平台。分别进行了电离注入和密度梯度注入的级联加速实验。通过优化电子进入低密度加速级的注入相，仅用2 mm的加速距就离获得了能量超过0.5 GeV、能散度为3%的准单能电子束。把第二段加速级的长度加长到5mm，获得了峰值能量超过1 GeV的准单能电子束。 2. 参与了各个监测系统的搭建和使用。利用光栅光谱仪监测电离产生的激光光谱蓝移和尾波场形成所产生的光谱红移，从而分析电离程度和尾波场的大小。利用磁光法拉第旋转效应获得了时间分辨的磁场，从而有效监控电子在注入级的注入和在加速级的加速。利用迈克耳逊干涉仪测量等离子体密度通道，从而有效监控激光在等离子体中的导引。 3. 基于唯象模型分析了隧穿电离注入的动力学过程。发现要使隧穿电离注入发生，超短超强激光脉冲的光强存在一个上限，即当激光光强超过一定值时，电离注入不再发生。通过观察隧穿电离注入电子在激光和尾波场中的运动，发现在空泡机制下，垂直线偏振驱动激光偏振面方向，电子整体运动呈现出丝状结构和半相干的betatron振荡。 |
| 英文摘要 | Laser wakefield accelerator (LWFA) can provide 3 orders higher acceleration gradient than the conventional radiofrequency accelerator, therefore it is the ideal electron source for the table-top free electron lasers. Single-stage LWFA can accelerate electron beams to the energy of GeV, but the energy spread is usually not that small and difficult to control. This is because that the injection and the acceleration of electrons, which have different requirement on the parameters of plasma and laser, are not independently controlled. While, cascaded LWFA can independently control the seeding and the acceleration of the electron beams, thereby acquiring high-energy monoenergetic electron beams beyond multi GeV. To obtain stable electron beams mentioned above, it is necessary to perfect the matching between the seeding stage and the acceleration stage of the cascaded LWFA. Based on the cascaded LWFA scheme, we carried out related experimental researches, and we also investigated the dynamics of tunneling-ionization-induced injection based on a phenomenological model, using theory and particle-in-cell (PIC). The main results and innovations are listed as follows: 1. We built up the experimental platform on ultra-short ultra-intense laser driven cascaded LWFA. We carried out cascaded LWFA experiments based on tunneling ionization-injection scheme and density gradient injection, separately. By perfecting the seeding phase of electrons, we got electron beams beyond 0.5 GeV with 3% energy spread, the acceleration distance is only about 2 mm. And if we further lengthen the accelerating stage to 5 mm, electron beams beyond 1 GeV were produced. 2. I participated in assisting building up monitoring system for cascaded LWFA. Grating spectrometer is utilized to observe the blue shift of laser pulse due to ionization and the red shift due to wakefield generation, so that we can estimate to what extent the ionization is and the amplitude of wakefield. A magnetic-optic Faraday polarimetry is used for time-resolved magnetic field measurements , which allowed us to monitor the processes of electron seeding and acceleration in the second stage. Finally, a Michelson Interferometry is used to observe the plasma channel, thereby providing the information about laser’s guiding in plasma. 3. We develop a phenomenological model to investigate dynamics of ionization-induced injection of laser wakefield acceleration (LWFA). It is found that there is an upper limit for laser intensity of ionization-induced injection, in another word, ionization-induced injection never happens if the amplitude of the laser is larger than some specific value. Besides, we look into the dynamics of ionization-induced injected electrons in the wakefield. As for the “bubble” regime, in the plane perpendicular to the polarization of linear polarized laser, ionization-induced injected electrons exhibit a filamented structure and semi-coherent betatron oscillation. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/16790]  |
| 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 | 陈强. 超强超短激光驱动的尾波场级联电子加速的理论和实验研究[D]. 中国科学院上海光学精密机械研究所. 2013. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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