基于相对论强激光的电子加速及相关物理问题的研究
文献类型：学位论文
| 作者 | 邓爱华 |
| 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 | 刘建胜 |
| 关键词 | 激光尾波场加速 等离子体加速器 相对论强激光 等离子体通道 相位控制 相干回旋振荡 辐射阻尼 自冷却 |
| 其他题名 | Electron Acceleration and Physics Issues Based on Relativistic Intense Laser |
| 中文摘要 | 超强超短激光的持续迅猛发展，为人类提供了前所未有的全新实验手段与极端物理条件。激光聚焦强度在过去的十多年里已提高了7-8个量级，实验室条件下已经能够达到聚焦强度1021 W/cm2乃至1022 W/cm2量级，激光脉冲的时间尺度已小于10 fs，接近激光光场的单个振荡周期。如此强的激光光场可将物质迅速电离形成等离子体，光和物质的相互作用也进入了强相对论非线性光学的全新范畴。在其推动下，基于等离子体的激光加速粒子、高次谐波和阿秒脉冲以及激光惯性聚变核物理等研究得到广泛关注，它们不仅在医疗、能源等方面具有重要应用，而且为探索粒子运动、结构以及性质等前沿基础物理问题提供了很强大的手段和条件。本论文开展了相对论强激光与等离子体相互作用进行电子加速以及相关物理问题研究，取得如下研究结果： 1. 搭建了相对论强激光与气体相互作用进行激光尾波场加速电子的实验研究平台，开展了百太瓦强度飞秒激光与氢气喷流相互作用进行电子加速实验研究。在1 mm喷嘴长度情况下，通过改变气体的背压，实现对等离子体密度的控制，研究了不同等离子体密度条件下激光加速电子的情况，获得了总电量约为10 nC、截止能量约为10 MeV、电子有效温度约为4 MeV的电子束。增加气体喷流长度到1.5 mm时，电子的能量和有效温度进一步提高，获得了电量约为2.6 nC，截止能量为80 MeV，有效温度为26.2 MeV的电子束。利用所产生的高电量的电子束轰击钛膜，由轫致辐射产生高能量的X射线，对不同结构、不同材料的固体靶材进行成像探测。 2. 系统研究了利用烧蚀型毛细管在高压放电驱动下稳定产生预制等离子体通道的参数条件，并利用光谱方法对通道结构进行了时间和空间分辨测量。开展了百太瓦级激光在预制毛细管通道中进行电子加速的实验研究，成功实现了160 TW飞秒激光脉冲在4 cm长度的放电烧蚀毛细管通道中的导引，获得了最大能量达1.8 GeV的高能电子束。 3. 设计了由两段不同密度等离子体组成的级联尾波场加速器，第一级中加速产生的电子束能够被注入到第二级等离子体中进一步被加速。二维粒子模拟研究了通过控制注入级中的电子束的注入和加速，可实现注入级产生的电子束在时间和空间上与加速级尾波场的加速相位完全匹配。在注入级加速中，电子的注入和加速依赖于尾波场的演化，通过改变激光的聚焦位置和等离子体密度分布，能够使得产生的电子束注入到加速级的最大加速场中，从而在最大程度上改善电子束的能散度。二维粒子模拟通过选取合适的激光参数和聚焦位置，等离子体密度条件等，最终可实现消除暗电流的级联尾波场加速器，获得700MeV，能散度0.6%，横向发散角为1.4π mm mrad的单能电子束。 4. 研究了等离子体密度的选择和操控对等离子体加速器中电子束的性能和动力学行为的影响。研究了在线性机制下( )，单级激光等离子体加速器中的各个参数与等离子体密度的关系，并给出了不同密度情况（1015 ~ 1018 cm-3）下能量1 TeV的多级加速器的参数设计，分析了由于同步辐射能量损失引起的电子动力学的演化，并利用二维粒子模拟验证了不同密度下尾波场的定标率。 5. 考虑电子束回旋振荡引起的辐射阻尼作用，通过数值解析方法描述等离子体加速器中电子束的动力学行为，研究了电子的能量、能散度和横向发散角在加速过程中的演化，发现了辐射阻尼作用引起的电子束的自冷却效应。研究结果表明，加速的初始时刻，随着电子能量的增加，其相对能散度降低，横向发散角增大；随后由于回旋振荡引起的辐射阻尼作用，电子束的发散角以恒定的速率逐渐减小。研究发现辐射阻尼率为一常数 ，且与初始电子束的性能参数以及激光尾波场参数均无关。电子束的自冷却效应能够使得电子束能被加速至TeV甚至PeV量级，归一化发散角和能散度的降低能够满足高能物理的要求，如高能对撞机、高亮度的γ射线的产生等，且对天文学和高能宇宙射线的研究具有很大的帮助。 |
| 英文摘要 | The rapid development of ultra-short and –intense laser provides new experimental means and extreme physical conditions as never before. The peak focusing laser intensity in the past decade has been improved 7-8 of magnitude, reaching 1021 W/cm2 even up to 1022 W/cm2 under laboratory conditions, and also the laser pulses with duration less than 10 fs are available, which is close to a single cycle of oscillation of the laser light field. Such a strong laser field can quickly ionize materials to plasma, leading the laser-matter interaction to enter the highly relativistic nonlinear optical category. Under its impetus, researches on laser particle acceleration, high-order harmonic and attosecond pulse laser generation, inertial fusion and nuclear physics have attracted widespread attentions. These researches are not only significant in the applications such as medical treatment, energy resource, but also offering a powerful tool for exploring the frontier and fundamental physical issues like the nature of basic particles motions, structures and properties. In this thesis, the investigations on relativistic intense lasers interaction with plasma for electron acceleration and related physical issues are performed. Some results are obtained as list below: 1. An experimental platform on relativistic intense laser-gas interaction for laser wakefield acceleration has been built up to investigate the electron accelerations from the interaction of hundred terawatts (TW) intense femtosecond laser with hydrogen jet. With 1 mm hydrogen length, by changing the gas backpressure, it can be realized to control the density of the plasma, and the experiments on electron acceleration with different plasma density are carried out, obtaining electron beams with the total charge about 10 nC, cut-off energy of approximately 10 MeV, effective temperature about 4 MeV. When the length of gas jet is increased to 1.5 mm, electron energy and the effective temperature increase further, and finally an electron beam with the charge of 2.6 nC, cut-off energy of 80 MeV and effective temperature of 26.2 MeV was obtained. Impacting the titanium film with such high charge electron beam, high energy X-ray can be produced by bremsstrahlung radiation, which has been successfully used for imaging detections of different structured solid targets. 2. The generation of preformed plasma channel driven by discharge in ablative capillary is investigated, and the conditions for generating plasma channel stably, the space and time resolved measurements of the plasma channel structures are studied. The experiments of electron acceleration based on the hundred TW laser interaction with the preformed capillary channels are carried out, the successful optical guiding of ultraintense laser pulsed with peak powers up to 160 TW over a 4-cm long ablative caplillary discharge plasma channel are demonstrated. Electron beams, with energies up to 1.8 GeV, are generated by using the 130 TW, 55 fs driving laser pulse. 3. Two segments of plasmas with different densities, which are operated as the electron injector and accelerator, respectively, are designed to realize a cascaded laser wakefield accelerator. 2D particle-in-cell simulations indicate that the perfectly phase matching between the wakefields and the seeded electron beams can be realized by controlling of the electron dynamics in the first stage. In the first stage plasma, electron injection and acceleration owing to the evolution of plasma wake is analyzed. By adjusting the focus of the laser beam and plasma density distribution, the electron seeding phase relative to the second-segment plasma wave can be optimized to obtain the maximum acceleration rate in the second stage of the cascaded LWFA, therefore the energy spread can be greatly improved as well. And finally a 700 MeV electron beam with a relative rms energy spread of about 0.6% and the normalized transverse emittance of 1.4π mm mrad was obtained after a 5.5-mm-long acceleration in a dark-current free cascaded laser wakefield accelerator. 4. Issues of operating plasma density are investigated to control the electron beam properties and beam dynamics in plasma-based accelerator. In quasi-linear regime ( ), the formulae for designing a single stage are obtained as a function of the operating plasma density and the design examples of the laser plasma accelerator linac with the beam energy of 1 TeV are presented at the operating plasma densities of 1015 ~1018 cm-3. The design formula and scalability on the plasma density for the single laser plasma accelrator stage are confirmed by scaling the 2D particle-in-cell simulations, carried out in the range of the plasma density of 1018 ~ 1019 cm-3. 5. Electron beam dynamics on transverse emittance and energy spread with considering radiation reaction effects are studied numerically. It is found that the emittance growth and the energy spread damping initially dominate and balance with radiative damping due to the betatron radiation. Afterward the emittance turns to decrease at a constant rate and leads to the equilibrium at a nanometer radian-level with growth due to Coulomb scattering at PeV-level energies. A constant radiation loss rate is found independent of the electron beam and plasma conditions. Self-cooling of electron beams due to betatron radiation may guarantee TeV-range linear colliders and give hints on astrophysical ultrahigh energy phenomena. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15712]  |
| 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 | 邓爱华. 基于相对论强激光的电子加速及相关物理问题的研究[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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