相对论性强激光对电子和离子的加速以及在低密度等离子体中的传输
文献类型：学位论文
| 作者 | 王精伟 |
| 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 | 余玮 |
| 关键词 | 相对论性激光脉冲 反相位交叉光 电子连续加速 激光自导引 离子辐射压加速 台式中子源 PIC 模拟 |
| 其他题名 | Relativistic laser acceleration of electrons and ions and propagation in underdense plasmas |
| 中文摘要 | 自1960年激光发明以来，激光与等离子体的相互作用就逐渐成为物理学中一个非常重要的研究领域。随着激光技术的发展，特别是啁啾脉冲放大（CPA）技术的发明，目前人们已经能够获得脉宽小于5 fs，功率密度为10^{22} W/cm^2的超短超强激光脉冲。这种强度的激光与等离子体相互作用又激发了很多新的研究热点，比如高能量的电子、离子的产生，激光在等离子体中的长距离传输，激光驱动核反应等。这些研究在很多方面有着很重要的应用，例如医学治疗，成像诊断，台式中子源，以及惯性约束聚变等。在理论研究方面，由于等离子体中的电子在这种强度的激光作用下的运动是相对论运动，所以强激光与等离子体相互作用理论必须考虑各种相对论效应。本论文主要从理论和计算机模拟上研究了反相位交叉光对电子的加速，相对论性激光在低密度等离子体中的传输，以及超强激光对固体靶离子的加速问题。主要内容包括： 1. 研究了反相位交叉光束对电子以及电子薄膜靶的加速过程。由于两束光相位相反，轴上的磁场、横向电场都相互抵消，而仅有的轴向电场类似尾波场一样对电子加速。电子在横向上没有动量和位移，所以电子能被多个激光脉冲对连续的捕捉而实现多级加速，在大约2 mm的距离内获得GeV的能量。同时通过粒子模拟（PIC）还发现，交叉激光比同能量的单束激光能更加迅速的将靶中的电子加速到更高的能量，此时靶的密度还维持在一个比较高的水准。这种加速方式在某些应用中，比如产生X射线的飞镜，具有比较好的效果。 2. 用解析方法研究了强激光脉冲在低密度等离子体以及预等离子体管道中的传输。发现在这两种情况下的自导引机制是完全不同的。当激光脉冲在均匀等离子体传输时自洽形成的电子空腔有足够陡峭的密度梯度时，激光脉冲能在其中实现稳定的自导引传输，且激光半径几乎没有变化。而在预等离子体通道中，激光的导引主要由光散射和聚焦平衡导致。管壁等离子体能降低局域的电介系数，进而能聚焦激光。计算结果表明光脉冲在均匀等离子体中自导引需要几十TW的功率，而在预等离子体中却能在TW量级就能实现。 3. 用PIC模拟研究了超强激光对微米量级的固体小靶直接加速的过程。激光通过辐射压力对电子加速，电子运动造成的电荷分离场加速后面的离子。当激光足够强时，辐射压力能和离子对电子的回复力基本平衡，电子离子一起向前运动，离子呈现比较好的单能性。由于离子间相互的库仑作用力得到抑制，等离子体能够维持在比较高的密度。我们利用这种加速方案下的高能离子轰击另一个静止的，尺寸相对比较大的靶。高能离子几乎都沉积在静止靶中，离子动能转化为系统的热能，中间高密度区域的平均能量大约在1.14 MeV，非常有利于中子的产生。根据模拟结果可以估计中子的产额为10^7个/shot，比用团簇的产额高了大约3个数量级。 |
| 英文摘要 | The study on interaction of laser and plasmas is becoming one of the most important areas in physics science since the invention of laser in 1960s. The fast development of this area really depends on the advance of laser technology, especially the advent of chirped-pulse amplification technique. The pulse duration has reduced from a few tens of picoseconds in the mid-1980s to a state-of-the-art shorter than 5 fs with an intensity of 10^{22} W/cm^2. Many new hot spots have been triggered by such intense laser, including high energy particles production, laser pulse long propagation in underdense plasmas, laser driven nuclear reaction. All these researches might possess a number of useful applications, such as medical therapy, imaging, inertial confinement fusion, and so on. The theory of interaction of laser and plasmas should involve all kinds of relativistic effects as the plasma electrons in such intense laser field make relativistic motions. This thesis is devoted to theoretical and numerical studies of the interaction of relativistic laser and solid state target and laser propagation in underdense plasmas. The first part is about electrons and electron foils acceleration by crossed laser beams with opposite phases (CLBOP). The transverse electrical field and magnetic field along axis will be cancelled respectively because of the opposite phases, leaving the only axial electrical field which accelerates electrons like a wake field. The energetic electrons will move along the axis without any transverse momentum and displacement. In this sense, the electrons can be accelerated to high energy by successive laser pulses. The particle in cell (PIC) simulation shows that electron foils can be accelerated by CLBOP to high energy much faster than using one normally incident pulse with the same laser energy. The second part is devoted to investigate the guiding of laser pulse in uniform plasmas and preformed plasma channels. The self-guiding mechanisms for these two cases are quite different. It is found that an intense laser pulse can be steadily self-guided in underdense plasmas with nearly a constant spot size if the self-consistently generated electron cavity has a sufficiently steep density gradient at the edge. In a preformed plasma channel, however, laser guiding is maintained mainly by the balance between the light diffraction and focusing. The latter is induced by the wall plasmas which greatly reduce the local dielectric constant. It is shown that the self-guiding of a laser pulse in uniform plasmas requires tens of terawatts power, but those that are in preformed channels can be realized with only a terawatt power. The third part is devoted to study the ultra-intense laser acceleration of a micron-size projectile. Moving electrons accelerated by the laser radiation pressure will pull the ions behind via the charge separation field. When the laser intensity is high enough, the radiation pressure can equal the restoring force from the ions. In this scenario, all particle species are accelerated to the same velocity and eventually propagate ballistically as a neutral plasma bunch. The projectile accelerated by such ultra-intense laser is then impinged on a dense plasma target and merges with the latter. Part of the kinetic energy of the laser-accelerated ions in the projectile is deposited in the fused target, and an extremely high concentration of plasma ions with a mean kinetic energy needed for fusion reaction is induced. The interaction is thus useful as a compact neutron source. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15679]  |
| 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 | 王精伟. 相对论性强激光对电子和离子的加速以及在低密度等离子体中的传输[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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