超短超强激光驱动粒子加速与正电子产生研究
文献类型：学位论文
| 作者 | 徐同军 |
| 学位类别 | 博士 |
| 答辩日期 | 2016 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 沈百飞 |
| 关键词 | 超短超强激光 正电子产生 质子加速 低能散氩离子 |
| 其他题名 | Ultra-short Ultra-intense Laser Driven Particle Acceleration and Positron Generation |
| 中文摘要 | 随着激光技术的快速发展，尤其是啁啾脉冲放大技术（CPA）的提出和实现，近来实验室中已经能够获得聚焦强度超过1022 W/cm2、单脉冲宽度小于10 fs的相对论激光脉冲。超强激光与等离子体相互作用应用广泛，例如粒子加速、高次谐波与阿秒脉冲产生、激光正电子源以及强场核物理等领域。超强激光驱动的离子加速是备受人们关注的研究热点之一，得到的高能离子可以用于质子成像、离子治疗、传统加速器注入及惯性聚变快点火等诸多方面。作为电子的反粒子，正电子在反物质科学、天体物理与材料检测等方面具有广泛的应用价值。在这些正电子基础科学及应用研究中，正电子源一直是最为根本的。目前, 基于放射性同位素与传统电子加速器产生的正电子束一般脉宽较长、密度也不高，难以满足天体物理等应用的需求。相对论强激光驱动产生的正电子源由于其高产额、短脉宽、高密度等优势已然成为正电子领域的热门。基于以上几点，本论文主要做了以下几个方面的工作： 1. 利用超强飞秒激光进行了基于激光加速电子的正电子产生实验研究。所用激光装置为中科院上海光学精密机械研究所强场激光物理国家重点实验室的飞秒拍瓦激光装置。国内首次在实验上得到了高强度、高密度的超短MeV正电子束。利用超强激光与高密度气体靶相互作用，加速得到具有大电荷量的相对论高能电子束。然后，高能电子束照射高Z固体靶，得到了高密度的MeV正电子束。实验中厚靶条件下产生的电中性的电子-正电子等离子体可以用于实验室天体物理的研究。同时， MeV正电子束是超快的，脉冲宽度仅为数十个飞秒，因而其峰值强度高达7.8×1021 s-1。 这种超快的正电子束可用于高分辨地研究毫米厚度材料的快动力学过程，并在正电子湮没谱学方面具有潜在应用前景。 2. 为了在正电子产生实验中精确地探测正电子，设计制造了正电子谱仪。正电子产生过程中，正电子的产额远远低于电子和高能光子，甚至是多个数量级的差距。即正电子的出射过程中伴随有大量的电子出射和强烈的伽马辐射。所以在正电子产生实验中，正电子的精确检测是保证实验顺利完成的关键。为此，我们特别设计制造了屏蔽噪声的正电子谱仪用于正电子的检测。 3. 理论上提出了一种新型的基于无碰撞静电激波（collisionless electrostatic shock，CES）的级联质子加速方案。利用超强激光辐照固体靶产生一个稳定的CES场，对另一束外注入的质子束进行加速。通过计算模拟和理论分析，发现一束初始能量为55MeV的质子源能够被进一步加速到265MeV并保持较窄的能散分布。这一方案为利用现有的高强度激光装置产生能量为数百MeV的质子束提供了一条可能的途径。 4. 在强场激光物理国家重点实验室飞秒拍瓦激光装置上进行了基于超强激光与团簇气体靶相互作用从而加速产生纯净离子的实验研究。脉宽为45 fs的相对论激光脉冲与氩气团簇靶相互作用，在实验上产生了一束高准直的窄能散氩离子束。该氩离子束带有高电荷态Ar16+，在能量峰0.39 MeV/核子处具有最小绝对能散0.19 MeV/核子。基于PIC模拟，提出了一种新颖的机制可以大大降低离子束的能散。相对论激光脉冲驱动产生的强等离子体尾场对离子束的能谱具有很强的调制作用——尾场可以去掉离子能谱的低能部分。由库仑爆炸得到的预加速氩离子经过激光尾场调制后能散下降并且准直性变好。基于相对论激光与团簇气体靶的相互作用，这种新颖的机制可以提供多种高能离子。实验产生的窄能散高品质重离子束可以为许多应用带来重大进展，如医学治疗、核物理和传统加速器的注入级。实验结果也第一次揭示了等离子体尾场对激光驱动的MeV离子束的调制作用。 |
| 英文摘要 | With the rapid development of laser technology, especially the proposal and realization of chirped pulse amplification (CPA) technique, laser pulses with peak intensity above 1022 W/cm2 and pulse duration below 10 fs are available in labrotary recently. The interaction of ultra-intense laser with plasma has wide applications, such as particle acceleration, high harmonic and attosecond pulse generation, laser-driven positron source and high field nuclear physics. Laser-driven ion acceleration has attracted much attention since the accelerated ions with high energy have various potential applications, such as proton radiography, ion therapy, injector of conventional accelerator and inertial fusion fast ignition. As the anti-particle of electrons, positrons have extensive applications in anti-matter science, astrophysics and material detection. In both fundamental and applied studies, positron sources are always essential. However, the positron beams generated from radioactive isotopes and conventional electron accelerators usually have long pulse duration, thus low beam densities, which are not appropriate for astrophysical experiments or other applications. Laser-driven positron sources have attracted broad interests due to their superiorities of high yield, short pulse duration, and high density and so on. Based on these conceptions, specific results in this thesis are follows: 1. Experimental demonstration of positron generation based on laser-accelerated electrons have been carried out by using the femtosecond petawatt laser system at State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences (CAS). Experimental generation of ultrashort MeV positron beams with high intensity and high density using a compact laser-driven setup is reported. A high-density gas jet is employed experimentally to generate MeV electrons with nC-scale charge; thus, a charge-neutralized MeV electron-positron plasma with high density is obtained during laser-accelerated electrons irradiating high-Z solid targets. It is a novel electron–positron source for the study of laboratory astrophysics. Meanwhile, the MeV positron beam is pulsed with an ultrashort duration of tens of femtoseconds and has a high peak intensity of 7.8×1021 s-1, thus allows specific studies of fast kinetics in millimeter-thick materials with a high time resolution and exhibits potential for applications in positron annihilation spectroscopy. 2. A positron spectrometer is designed and manufactured for the precise detection of generated positrons in the experiments. Since the positron yield is considerably below electrons and energetic photons, that is to say, positrons are ejected from the high-Z material target with a large number of electrons and gamma rays, precise detection of generated positrons plays a critical role in experiments. A positron spectrometer is specially designed to avoid the background noise and manufactured for the precise detection of generated positrons. 3. A new scheme for proton acceleration by cascaded collisionless electrostatic shock (CES) is proposed therotically based on particles in cells (PIC) simulations. By irradiating a foil target with a moderate high-intensity laser beam, a stable CES field can be generated to be employed as the accelerating field for another external-injected proton beam. The mechanism is in details studied through simulations and theoretical analysis, showing that a 55MeV seed proton beam can be further accelerated to 265MeV while keeping a narrow energy spread. This scheme offers a possible approach to produce proton beams with energy of hundreds of MeV by existing available high-intensity laser facilities. 4. Experimental study of pure ion acceleration and generation based on the interaction of ultra-intense laser with gas targets have been carried out by using the femtosecond petawatt laser system at State Key Laboratory of High Field Laser Physics. A highly-collimated argon ion beam with narrow energy spread is produced by irradiating a 45-fs fully-relativistic laser pulse onto an argon cluster target. The highly-charged (Ar16+) heavy ion beam has a minimum absolute energy spread of 0.19 MeV/nucleon at the energy peak of 0.39 MeV/nucleon. Based on PIC simulations, we identify a novel scheme that greatly reduces the beam energy spread. The intense plasma wakefield driven by the fully-relativistic laser pulse has a strong modulation on the ion beam in a way that the low energy part is cut off. The pre-accelerated argon ion beam from Coulomb explosion thus becomes more mono-energetic and collimated. This novel scheme will provide various ion species based on cluster-gas target. The generated high-quality heavy-ion source with narrow energy spread may afford significant advances in many applications including medical therapy, nuclear physics, and injector of conventional ion accelerators. These experimental results reveal for the first time the modulation of plasma wakefield on MeV laser-driven ion beams. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15998]  |
| 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 | 徐同军. 超短超强激光驱动粒子加速与正电子产生研究[D]. 中国科学院上海光学精密机械研究所. 2016. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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