强飞秒激光脉冲与等离子体相互作用中电子与离子加速的若干问题研究
文献类型：学位论文
| 作者 | 刘明伟 |
| 学位类别 | 博士 |
| 答辩日期 | 2010 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 李儒新 |
| 关键词 | 强飞秒激光脉冲，烧蚀型毛细管，等离子体通道，光导引，电子加速，固体薄模靶，离子加速，肿瘤治疗方法 |
| 其他题名 | Electron and ion acceleration from intesne laser pulse interaction with plasmas |
| 中文摘要 | 激光技术的飞速发展使得人们可以在飞秒时间尺度范围内实现拍瓦量级的激光瞬时功率输出。可以获得的激光强度超过1022 Wcm-2，而单个脉冲宽度也可以小于10fs。等离子体介质由于没有破坏域值限制，能够承载的加速梯度比传统加速器要高几个数量级。利用强飞秒激光脉冲与等离子体相互作用可以在非常短的距离内把电子或离子加速到很高能量。而所使用的超短脉冲激光装置一般都已实现小型化，基于超短脉冲激光与等离子体相互作用的台面型激光粒子加速器的研究得到越来越多的重视。 本论文主要是从实验和理论上，并部分利用PIC粒子模拟方法，对强飞秒激光脉冲与等离子体相互作用中加速电子和离子及其应用的相关问题进行研究。 主要包括： 1. 从理论上研究了等离子体通道中强激光束的导引。由于使用非弱相对论近似微扰展开的方法，避免了考虑高阶非线性等的局限性。详细分析了相对论通道耦合效应对通道中激光传输特性的影响，并推导了新的匹配传输条件。在使用预等离子体通道导引激光的激光尾波场加速实验中，指向抖动将导致主激光束偏离通道中心轴入射，使主激光与通道之间的准直性变差，从而影响激光的导引效果和电子的加速效率。提出了考虑光束指向抖动影响的离轴入射模型，并导出了通道中各相应光束参量的演化方程。根据所提出的表示光束指向抖动影响大小的参数和通道的有效范围，可以得知存在光束指向抖动时通道等对主激光的导引的有效性。 2. 搭建了利用烧蚀型毛细管放电产生等离子体通道的实验平台，系统研究了可以稳定重复产生等离子体通道的参数条件，利用光谱方法对通道结构进行了时间和空间分辨的测量，并演示了产生适用于10GeV量级激光尾波场电子加速的低密度等离子体通道。提出了激光横向触发毛细管放电的方法。该横向触发放电方法可以克服原有激光纵向触发放电方法的局限性，并适用于采用毛细管放电等离子体通道导引激光的级联加速方案。 3. 基于上海光机所强场激光物理国家重点实验室自建的拍瓦激光装置，搭建了利用烧蚀型毛细管放电产生等离子体通道导引激光的激光尾波场电子加速实验平台。并进行了系列的超强超短激光脉冲的导引实验和电子加速实验。实验上演示了入射功率为160TW的超强飞秒激光脉冲在4cm长等离子体通道中的导引。通过改变毛细管材料，从实验上验证了高阶光电离注入在含氧的烧蚀型毛细管电子加速实验中的重要性，并得到了最大能量大于1GeV的电子加速实验结果。提出了前端毛细管使用含氧材料、后端毛细管使用不含氧材料组合的方式来演示激光级联电子加速的实验方案，在实验中得到了具有准单能特征的信号。 4. 在双层靶试探粒子加速机制中，一般假设背景离子是均匀分布。但所使用的激光脉冲长度等条件不同时，会对背景离子的密度分布造成影响。对激光脉冲长度与背景离子密度分布之间的关系做了定性分析，从理论上研究了背景离子密度梯度分布对轻离子加速的影响。 5. 重离子束在肿瘤治疗方面具有一系列的优点，但传统加速器的高昂造价使得该方法难于推广；目前临床使用的光动力疗法的治疗效果也由于光源和肿瘤区域氧含量等受到限制。激光离子加速器被认为可以降低加速器的成本，但短时间内难以同时达到肿瘤治疗对离子束能量和数目的要求。大剂量的离子束也不适合直接用于危险组织的肿瘤治疗。提出了利用激光加速氧离子进行放射治疗并驱动光动力疗法的肿瘤综合治疗方案，可以在一定程度克服两种方法单独使用时的局限性，从而加快重离子束放射治疗的推广。利用一维PIC模拟程序，在氧化物薄模靶中模拟了激光准单能氧离子加速，初步验证了该方案的可行性。 |
| 英文摘要 | The rapid development of laser technology has lead to the realization of femtosecond lasers with petawatt instantaneous output. Especially, lasers with intensity larger than 1022 Wcm-2 and/or pulse duration shorter than 10 fs are now available. Because there is no damage threshold, plasmas can sustain electric fields several orders of magnitude larger than those used in traditional accelerators. Electrons and ions can be accelerated to high energy within a very short distance by laser-plasma interactions. Moreover, the ultrashort laser systems used in these acceleration experiments are typically “table-top”. This makes it is also possible to construct compact “table-top” laser particle accelerators based on laser-plasma interactions, which attracts more and more attention. In this thesis, we mainly focus on experimental and theoretical investigations on the laser electron and ion acceleration. Some results are also obtained by means of particle-in-cell (PIC) simulation. The main results are given as follows: 1. Optical guiding of intense laser beams in plasma channels is studied theoretically. The use of nun-series-expansion method prevents the limitations such as considering higher-order nonlinearity. The effect of relativistic-channel coupling is analyzed in detail. Correspondingly, a modified matched-condition is obtained. In the laser wakefield acceleration experiments using preformed plasma channels, beam pointing fluctuation always reduces the beam alignment precision, which decreases the efficiency of optical guiding and electron acceleration. We present an off-axis incident model to analyze the influence of beam pointing fluctuation on the beam propagation properties. The evolution equations for the beam spot size and centroid are obtained. According to the parameter related to the intensity of beam pointing fluctuation and the effective (transverse) channel region, the feasibility of optical guiding can be known when there presents beam pointing fluctuation. 2. By means of ablative capillary discharges, systematic experiments are carried out on the generation of plasma channels with high repetition, such as the dependence on the discharge parameters, the temporal and spatial measurement of the plasma density, and the demonstration of generating low density plasma channels for 10-GeV-class electron acceleration. A laser transverse ignition method is developed, which can reduce the limitations of the laser longitudinal ignition method. Especially, this transverse ignition method is quite suitable to be used in the staged laser electron acceleration schemes. 3. Based on the SIOM Petawatt laser, a laser wakefield acceleration system is developed, using the ablative capillary discharge plasma channel to guide the driving pulse. A series of optical guiding and acceleration experiments are carried out, such as the demonstration of guiding a 160 TW laser pulse over a 4 cm plasma channel. Using capillaries with different material, field ionization injection mechanism is demonstrated to be important for electron acceleration using ablative capillary discharge plasma channels. Generation of electron beams with the maximum energy larger than 1 GeV is also achieved in our experiments. Moreover, by combining the capillary with different material, i.e., the front segment with oxygen while the back one without oxygen in the experiments, we demonstrate the generation of quasimonoenergetic signals, although further experiments are still in proceeding. 4. In the test particle model for ion acceleration from laser irradiated coated foils, the substrate-ions are commonly assumed to be uniform. In fact, the substrate-ion density will present gradients when the laser pulse durations are different, which is analyzed qualitatively. The influence of the substrate-ion density gradient on the light-ion acceleration is then investigated. 5. There is a series of advantages for ion beams on tumor therapy. But only few patients can benefit from this ion beam therapy (IBT), because of the large cost of traditional accelerators. In comparison, the photodynamic therapy (PDT) for tumor is one of the clinic methods widely used. But PDT is less efficient in the case that the treatment volume is deep inside the body, since the laser energy decreases exponentially along its propagation path. Moreover, PDT is also limited by the dependence on the oxygen content in the tumor area. Laser ion acceleration is believed can be used to contrast compact and cost-receivable ion accelerators. But it is difficult to satisfy the requisite both on the ion energy and number for therapy purpose. Moreover, an ion beam with large dose is not suitable to be used directly to the tissues in danger. We propose a combination oxygen-ion-photodynamic therapy method, which can take full advantages of IBT and PDT but release the requisite on the incident ion number. We also perform one dimension PIC simulation for laser oxygen ion acceleration from an oxide foil, and the results sustain the feasibility of the proposed combination therapy method. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15653]  |
| 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 | 刘明伟. 强飞秒激光脉冲与等离子体相互作用中电子与离子加速的若干问题研究[D]. 中国科学院上海光学精密机械研究所. 2010. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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