激光尾场加速电子束的优化及传输控制的相关研究
文献类型：学位论文
| 作者 | 方明 |
| 文献子类 | 博士 |
| 导师 | 李儒新 |
| 关键词 | 激光尾场加速器 Laser wakefield accelerator, electron acceleration 电子加速 shockwave induction 激波诱导 plasma pinnacle structure 等离子体尖峰结构 downramp injection 下降沿注入 long-distance beam transport 长距离束流传输 |
| 其他题名 | Studies on the Optimization and Manipulation of Electron Beams from Laser Wakefield Accelerators |
| 英文摘要 | 基于加速器的粒子束及射线源广泛应用于超快过程诊断到粒子束治疗等各个领域。激光尾场加速器为紧凑型加速器的实现提供了可能。在激光与等离子体相互作用产生的尾波内，电场梯度可高达100 GV/m，比传统加速器高了三个量级，非常适用于电子束团加速。通过这个强电场，激光尾场加速器在理论上可以在远小于传统加速器的加速距离内实现相同的能量增益。激光尾场加速器的发展和进步不仅对基础科学研究意义重大，而且在实际生活中也有巨大的应用前景，是非常值得深入研究的课题方向。 本论文针对激光等离子体尾场的电子束的品质优化和传输控制进行了探究，在等离子体密度构造、激波动力学、电子束的能散压缩、聚焦元件对电子束的作用等方面进行了理论、数值模拟和实验的深入分析，具体工作和取得的成果如下： 1. 参与搭建了百太瓦激光驱动的级联尾场加速实验平台，获得了高品质电子束，同时搭建了基于此电子束的长距离束线传输和波荡器辐射的实验平台。通过调节级联喷气结构，控制种子电子束的注入、加速以及能量啁啾调制等物理过程，在实验上成功地获得了能量为200 ~ 600 MeV、能散为0.4 ~ 1.3%、电量为10 ~ 80 pC、发散角为0.1 ~ 0.3 mrad的高品质电子束输出。该电子束的六维相空间亮度达到6.5×1015 A/m2/0.1%，这一结果优于目前国际上报道的同类等离子体加速器的水平。 2. 搭建了基于激波的陡峭尖峰形状的等离子体密度结构，以实现更稳定高品质电子束的输出。从构成密度梯度的激波结构入手，对实验结构中的斜激波的产生原理进行了分析和讨论；对激波的各项参数（包括激波角度、激波位置、激波宽度以及激波前后的密度比率之间的关系）做了系统的研究，并结合实验结果分析了斜激波的参数对尖峰密度分布的影响。 3. 利用网格粒子数值模拟分析了电子束在等离子体中的动力学行为，研究了电子束在等离子体尖峰密度分布的尾场中的注入和加速的物理过程。与传统的刀片诱导的密度下降沿注入方案相比，由于等离子体尖峰结构前的密度较低，等离子体尾场是准线性的，且电子束注入发生在尖峰结构的下降沿区域的末端；电子束在尾场中加速时，经历了尾波场由负梯度到正梯度的变换过程，电子束的能散先增大后减小，最终得到压缩。从模拟角度分析了激波角度对电子束的注入电量、发射度以及电子束的峰值能量和能散的影响。 4. 探索了激光尾场加速的电子束在真空中长距离传输中的品质特征。首先给出了电子束从激光尾场到真空阶段的参数模拟，重新初始化束流线入口处的参数设定，解决了实验上的参数失配问题。随后，在实验上测试了电子束通过长距离束流线的传输特征，包括聚焦的电子束的形状尺寸、电子束发散角和电子束指向性，并得到了与模拟一致的结果。最后，从理论上分析了激光尾场产生的电子束在聚焦元件作用下的横向发射度的演化。 5. 搭建了激光等离子体加速电子束源的多功能聚焦装置。该装置针对于脉宽为飞秒量级的、超高流强、峰值能量抖动范围较大的脉冲电子束，包括具有可调控梯度的四块组合聚焦铁、延时控制器和脉冲响应的荧光板电子束成像系。该装置不但可以实现对激光等离子体加速器产生的电子束的有效聚焦，而且具有能量监测、指向监测以及多束团能量筛选等功能，具有操作简单、方便高效、反馈灵敏等优点。; Applications of accelerator-based particle beams and ray sources contain fields ranging from ultra-fast process diagnosis to particle beam therapy. Laser wakefield accelerator has made it possible to implement compact accelerators, within the wake generated by laser-plasma interaction, the electric field gradient can be up to 100 GV/m, which is three orders of magnitude higher than that of the conventional accelerators, and this is ideal for electron acceleration. Through this strong accelerating field, the desired particle beam with high energy can be generated within a much shorter accelerating distance than conventional accelerators. The development and progress of laser wakefield accelerators are of great significance, not only to basic scientific research but also to the applications in our real life. In a word, the research on laser wakefield accelerators is worthwhile for further exploration. In this dissertation, we investigated the optimization and manipulation of the electron beam in the laser wakefield. The issues such as plasma density structure, shockwave dynamics, electron energy compression, and the focusing effect of the magnetic element on the electron beam have been theoretically, numerically and experimentally studied. The detailed work and results are as follows: 1. As a contributor, based on a hundred-terawatts ultra-intense ultra-short laser system, we built up the experimental platform for high-quality electron beams from the laser cascaded wakefield as well as long-distance transport of the electron beams and undulator radiation. By adjusting the cascaded gas density distribution, the seeded electron injection, acceleration and energy chirp control have been achieved. In the experiments, high-quality electron beams with peak energies tunable from 200 to 600 MeV have been successfully obtained, which have possessed rms energy spread of 0.4—1.3%, integrated charge of 10—80 pC, divergence of 0.1—0.3 mrad. More significantly, the six-dimensional brightness is estimated as 6.5 × 1015 A/m2/0.1%, which is much higher than the results of the similar research ever reported in the world. 2. A plasma density pinnacle structure based on a shockwave is created to generate the stable electron beams with high qualities. The structure construction and the principle of oblique shockwave formation in the structure have been analyzed and discussed; the shockwave parameters (the shockwave angle, the shockwave position, the shockwave width, and the correlation of density ratios from and after the shockwave), have been systematically studied, and the effects of the oblique shockwave parameters on the pinnacle density distribution have been analyzed. 3. We performed particle-in-cell simulations to analyze the dynamic behavior of electron beam in plasma, and investigated the injection and acceleration process through the wakefield of plasma pinnacle density distribution. Compared with the conventional blade-induced density downramp injection approach, the lower density before the pinnacle, induced a quasilinear wakefield and a delayed beam injected phase at the very end of the pinnacle downramp region; when electron beams were accelerated in the wakefield, the wake’s slope has transferred from negative to positive, the energy spread increased then decreased, ultimately, electron beams had a small energy spread. From the perspective of simulation, shock angle can also affect the amount of beam charge, the emittance, and the evolution of the peak energy and energy spread of the electron beams. 4. We characterized the electron beam’s quality parameters during the long-distance transport in vacuum. Firstly, simulations during the transition from the laser-plasma stage to the vacuum stage were performed, in order to initialize the parameter settings at the entrance of the beam line, therefore, the experimental parameter mismatch was addressed. We then characterized the beam properties after a long-distance transport, including the focused beam profile, beam divergence, and directionality. These experimental results agreed well with the beam transport simulations. Finally, the effects of the focusing elements on the transverse emittance of the electron beam generated from laser wakefield accelerator were theoretically analyzed. 5. A multi-functional focusing device for laser-plasma-accelerated electron beam source was built. The device is based on pulsed electron beam with a femtosecond pulse width, ultra-high flow intensity, and a large range of peak energy jitter, including four combinations of quadrupoles with adjustable gradients, time delay controller and impulse response fluorescent plate electron beam imaging system, which can not only achieve effective focusing of the electron beams from laser plasma accelerator, but also has functions of energy monitoring, pointing monitoring, and multi-bundle energy screening. The device has the advantages of simple operation, high efficiency, and sensitive feedback. |
| 学科主题 | 光学 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31055]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 方明. 激光尾场加速电子束的优化及传输控制的相关研究[D]. |
入库方式： OAI收割
来源：上海光学精密机械研究所
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。