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chi20181128上海光机所刘建胜557453With the development of ultra-intense and ultra-short laser pulse techniques, especially the invention of chirped pulse amplification technique, light-matter interaction has got into the highly relativistic plasma regime, and provides a new method for extreme physics research. In this regime, many novel nonlinear physical phenomena, such as relativistic self-focusing of laser, laser proton acceleration, laser wakefield acceleration and relativistic high harmonic generation have been discovered. The laser driven based plasma accelerator therein can maintain a high acceleration gradient up to 100 GV/m, which is three orders of magnitude greater than traditional radio-frequency (RF) accelerator. It can accelerate the electrons up to GeV in centimeter scale, so the laser wakefield acceleration (LWFA) can cut the cost and reduce the accelerator scales enormously, and provides the possibility for the realization of compact tabletop accelerators. In the recent 40 years, many great progresses have been made on the improvement of high-quality electron beams from LWFAs and their related research fields. On one hand, the LWFAs have produced the electron beams exceeded 4 GeV, the energy spread can be decreased to < 1%, and the brightness of the electron beams can up to 6.5×1015 A/m2/0.1%, which can rival that in the RF accelerators. On the other hand, many results have been achieved in the generation of LWFAs based high-energy radiation sources, and the high brightness gamma rays with energy up to MeV scale have been achieved. Therefore, the LWFAs have promising application prospect in the basic science research and the biomedical imaging, and the studies on the laser driven based plasma acceleration have not only the scientific significant but also the application value. This dissertation is aimed at the generation of multi-GeV scale electron beams and the diagnostic of electron beam parameters based on LWFAs by experiments and theory. By means of experiments and theory simulations, the plasma density measurements of ablative and gas-filled discharge capillaries, capillary discharge waveguides based LWFA experiments, transverse emittance measurements and the enhancement of Betatron radiation have been studied, and many original results have been achieved, which are listed below: 1. A gas-filled capillary discharge waveguide made of quartz is presented for the first time and the corresponding plasma channel is investegated. By measuring the plasma density and ablation level inside the capillary under different gas pressures and discharge currents, an optimized parametric-range that avoiding the ablation and suitable for the LWFA can be obtained, which is as follows: the peak discharge current range is 70–100A and the range of gas pressure is 7.5–14.7 Torr, corresponding to a controllable plasma density range of 5.0×1017 cm-3 - 1.0×1018 cm-3. 2. A phase-locking cascaded LWFA based on a tapered plasma density profile is experimental investigated for the first time by the quartz capillary presented above. A cascaded structure with a 6-mm gas nozzle and a 30-mm quartz capillary is used in experiments. By controlling the way of gas-injection in the capillary, a monotonically increasing plasma density profile can be formed. Then, by using ionization-induced injection, phase locked LWFA experiments are investigated and a high-energy electron beam with peak energy up to 2.3 GeV is achieved, which verified the scheme of phase locking acceleration. 3. A novel discharge capillary—hybrid capillary, is presented, and the high-energy LWFA experiments based on this hybrid capillary are investigated. The hybrid capillary is formed by injecting low-pressure hydrogen (<3.8Torr) into a pure ablative capillary. By measuring the plasma density evolution, a plasma channel and the matched spot size of the hybrid capillary can be obtained. Lastly, with two segments cascaded capillaries (30 mm + 30 mm), a high-energy electron beam with peak energy up to 3.2 GeV is achieved. 4. By designing a special distribution of gas flow, stable monoenergetic electron beams are produced and their corresponding transverse normalized emittance are also measured. Firstly, a two-gas-nozzle cascaded LWFA scheme based on a hundred-terawatts (TW) laser system is investigated. By constructing a special structure of gas density distribution, stable high-quality monoenergetic electron beams with peak energies of 340-360 MeV, RMS energy spread < 1% and RMS divergence of 0.15-0.4 mrad has been produced. Then, by measuring the corresponding Betatron spectra of the stable monoenergetic electron beams, the normalized transverse emittance can be estimated in a single shot, and the result is 56 ?m mrad, which, to the best of our knowledge, is the smallest value measured by experiments so far. As a main contributor, a novel scheme that enhance the electron beam transverse oscillation and the corresponding Betatron radiation by adjusting the plasma distribution is presented. By introducing a special structure of gas-flow, a tilted shock front region is formed. In experiments, by adjusting the location of the tilted shock front region, high-energy X ray sources with energies of 20 keV-30 keV can be produced.2019atalunwen2191211594612Laser Plasma Acceleration; Cascaded Acceleration; Discharge Capillary; Plasma Channel; Phase-lock Acceleration; Emittance, Betatron RadiationStudies on the Generation of High-Energy Electrons and Beam Diagnostic from Laser Wakefield Accelerators激光尾波场加速高能量电子束的产生及束流诊断研究超强超短激光技术的发展,特别是啁啾脉冲放大技术的发明,使光与物质的相互作用进入了相对论等离子体的范畴,为创造极端物理条件提供了新方法。在该范畴内,伴随着许多很新奇的非线性现象,比如激光的相对论自聚焦,激光质子加速、激光尾波场电子加速以及相对论高次谐波产生等。其中利用激光驱动的等离子体加速器的加速梯度高达100 GV/m,比传统的射频加速器高三个量级以上,它可以在cm量级的范围内将电子加速到GeV量级,从而极大地降低了加速器的规模和成本,为紧凑型台式化加速器的实现提供了可能。经过四十年的发展和积累,激光等离子体加速的电子束品质和相关的研究工作均取得了巨大的进展。一方面,在高能量方面已经产生了超过4 GeV的高能电子束,而在电子束的能散方面也已经达到了< 1%量级,电子束的亮度也超过了6.5×1015 A/m2/0.1%,可与传统加速器相媲美。另一方面,在基于激光等离子体加速器产生高能射线辐射源方面也取得了很多成果,产生了峰值能量在MeV以上的高亮度γ射线辐射源。因此,激光等离子体加速器在基础科学研究、生物医疗成像等方面都有巨大的应用前景,对激光等离子体加速器的研究不仅有重大的科学意义,还有实际的应用价值。 本论文立足于超强超短激光驱动的等离子体尾波场加速器,在数GeV量级高能量电子束产生和束流诊断等方面进行了实验和理论探索。论文在充气和烧蚀毛细管的等离子体密度测量、基于毛细管放电波导的高能量电子加速、电子束的发射度测量以及Betatron辐射增强等方面进行了研究,取得了如下主要研究结果: 1. 开展了利用石英玻璃充气放电毛细管产生等离子体通道的研究,对等离子体密度和烧蚀情况进行了测量和诊断。通过研究不同气体背压和电流条件下的毛细管内等离子体密度和电离度,获得了抑制烧蚀产生的且能够用于激光尾波场加速实验的最佳放电电流和气体背压条件:即放电电流70-100 A,气体背压7.5 Torr - 14.7 Torr,对应的等离子体密度范围为5.0×1017 cm-3 - 1.0×1018 cm-3。 2. 基于300 TW的驱动激光,利用石英玻璃充气放电毛细管开展了激光尾波场级联锁相加速实验。实验中,利用6 mm喷嘴和30 mm毛细管级联,首先通过优化控制毛细管的充气方式,使之形成具有单调递增的等离子体密度分布;其次采用电离注入方式,进行了基于等离子体密度变化的级联锁相加速实验,最终得到了峰值能量为2.3 GeV的高能电子束输出,验证了锁相加速的效果。 3. 设计了一种新型放电毛细管-充气烧蚀型混合毛细管,并利用混合毛细管进行电子加速实验。通过研究混合毛细管等离子体密度演化,得到了混合毛细管的通道窗口时间范围以及匹配半径。最后利用30 mm + 30 mm混合毛细管进行了级联加速,通过电离注入方式得到了峰值能量为3.2 GeV的高能电子束输出。 4. 通过设计特殊的气流分布,产生了稳定的高品质电子束,同时对电子束的发射度进行诊断。首先基于百太瓦激光驱动的级联加速器,通过构造特殊结构的气体密度分布,控制电子束的注入,从而得到了峰值能量为340-360 MeV、RMS能散< 1%,发散角为0.15-0.4 mrad的稳定电子束。其次通过测量Betatron辐射谱从而对电子束的横向发射度进行单发诊断,得到了电子束的横向归一化发射度为56 ?m mrad,该结果为目前国际上激光尾波场加速领域内测量到的最小结果。此外,还参与了通过改变等离子体密度分布从而增强电子束Betatron辐射的研究。实验中首先通过引入特定的气流分布结构形成一个倾斜激波区域,从而实现高品质电子束产生和横向振荡独立控制,其次通过改变倾斜激波的位置,实现了辐射能量范围为20-30 keV可控的高能X射线辐射源输出。激光等离子体加速;级联加速;放电毛细管;等离子体通道;锁相加速;发射度;Betatron辐射中国科学院上海光学精密机械研究所秦志勇等离子体物理博士
中文题目: 激光尾波场加速高能量电子束的产生及束流诊断研究
外文题目: Studies on the Generation of High-Energy Electrons and Beam Diagnostic from Laser Wakefield Accelerators
作者: 秦志勇
导师姓名: 刘建胜
学位授予机构: 中国科学院上海光学精密机械研究所
答辩时间: 20181128
中文关键词:
激光等离子体加速;级联加速;放电毛细管;等离子体通道;锁相加速;发射度;Betatron辐射
英文关键词:
Laser Plasma Acceleration; Cascaded Acceleration; Discharge Capillary; Plasma Channel; Phase-lock Acceleration; Emittance, Betatron Radiation
中文摘要:
英文摘要:
文献类型:学位论文
学位级别: 博士
正文语种: chi
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