| 题名 | 真空加速的优化及相关问题研究 |
| 作者 | 林海 |
| 学位类别 | 博士 |
| 答辩日期 | 2015 |
| 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 | 新加速机制，真空加速，激光 |
| 其他题名 | Study on Optimization of Vacuum Acceleration and Related Issues |
| 中文摘要 | 本研究论文初步探讨了通过针对性的设计人工电磁环境来实现经典电荷的加速的可行性。由于传统固态加速器受材料所限而只能以可控制的方式提供有限强度的加速电场，这使得从固态加速器获得高能物理及其他相关应用感兴趣的能量级的荷电粒子需要很大的尺寸。这就推动了对高效率加速的广泛深入的研究。除了继续研究对传统的固态加速器的改进，各种新型加速机制也引起了广泛关注。等离子体加速和激光真空加速是其中代表性的两种新机制。前者强调以超过固态材料耐受的强电场实现高效率加速并显著降低加速器尺寸。后者干脆不通过固态材料建立强电场，转而通过激光束的电场直接在真空中加速荷电粒子。两种新机制的可行性都已被大量的实验结果所证实，同时大量的相关理论研究也初步揭示它们的物理内容。既然被证明是可行的，下一步值得关注的就是如何发展它们。最直接了当的方法就是加大输入电磁刺激的强度已建立更强的加速电场。 本文所关注的不是这方面。相反，我们所研究的是在不增加投入的前提下，如何实现更高的产出。即如何更经济的使用外加电场和磁场。本论文所包涵的创新成果和研究进展如下所述： 1, 提出并验证了基于交叉传播的两束激光的真空加速的新构型。利用传统的光学技术把一束激光分成沿垂直方向传播的两束，并引入位相差π/2后再重新作一十字路口交会。这样的配置可以比一束激光配置更有效的加速荷电粒子。对于相同的总的激光能量，交叉束配置下的电子最大能量可以是单束配置下的最大能量的几十倍。对此现象我们给出了合理的物理解释。 2, 发展了关于上述工作所代表的多激励构型的真空加速的理论。提出并验证了如果把交叉束构型中的一束光以静电场取代，这种新构型可以导致荷电粒子的运动变成非时间周期性的（即一种时间周期性和时间单调性混合），而这种混合型运动对应着粒子动能的实质性增长。同样这种双激励构型比相同能量下的单激光束构型能产生更高的电子最大能量。 3, 提出了基于前述交叉激光束构型的另一个变异版本（即把一束光以静磁场取代）的真空加速的非微扰理论。和静电场版本类似，荷电粒子的运动是一种时间周期性和时间单调性混合。同样该变异版本比相同能量下的单激光束构型能产生更高的电子最大能量。 4, 提出并验证了交叉垂直配置的静电场和静磁场对传统固态加速器小型化的可行性。严格的理论和计算揭示，利用这样的场的配置可以使高能荷电粒子在很小的空间区域内发生180度的偏转，该空间区域的尺寸比传统的纯磁场偏转所需的空间尺寸小几个数量级。这从根本上保证了传统固态加速器小型化不再受巨大的偏转空间所制约。 5, 提出了真空中光束的横向形状的严格解。因光束的功率是有限的，电磁能量如何在横截面内分布是一个实际问题。传统的光学理论对这一问题的处理都是基于傍轴近似或慢变包络近似，虽然这些近似也能够导致光束的横向非均匀强度分布（即形状），这些非均匀形状的准确性是悬而未决的。我们的严格理论揭示了如何从合理的横向边界条件出发找出波动方程的严格（而非近似）的横向不均匀解。这对于准确的计算光与物质相互作用有着非常重要的意义。基于这样的严格解，我们证实了单束激光的真空加速的可行性。 6, 发现了荷电粒子粒子体系自洽场的准确宏观方程组。众所周知该体系的标准理论基础是Vlasov-Maxwell方程组是非常难以或几乎不可能做实际的6D计算（因太大的数据量）。即使对其现在最合理的处理技术PIC模拟，也难以做大时间-空间尺度的3D预报。尤其是在PIC模拟中，机时主要耗费在宏粒子一侧的信息更新中。我们从各种角度出发发现了自洽场所满足的准确宏观方程组，这对于快速准确的大时间-空间尺度的3D预报自洽场信息有着现实意义。 |
| 英文摘要 | This thesis is a preliminary investigation on how to make targeted design of man-made electromagnetic environment in order to accelerate classic charged particles. Because of material limits, conventional solid-state accelerators have to work on controllable finite-strength accelerating electric field, and hence are required to be of very giant size in order to achieve high energy particles interested by high energy physics and other related applications. This promotes broad and in-depth investigations on high-efficiency acceleration mechanisms. Beside improving conventional solid-state acceleration mechanism, other new mechanisms also win broad attention. Plasma-based acceleration and laser vacuum acceleration are typical examples of them. The former stresses usage of higher electric field beyond what the solid-state accelerator can sustain in the acceleration. As a result, the size of accelerator can be cut down significantly. The latter does not need solid material to set up accelerating electric field and directly uses laser electric field to accelerate charges in vacuum. Feasibilities of two new mechanisms have been confirmed by a lot of experiments, and underlying physics have been revealed preliminarily by a lot of theories. Now that being confirmed as feasible, their improvements are worthy of attention. The most straightforward way is to increase energy density of electromagnetic stimulus input in order to set up stronger accelerating electric field. This way is not the target of this thesis. On the contrary, what we will study is on how to get more output when the input is given, namely, on how to use applied electric and magnetic fields more economically. Major innovative results and progresses contained in this thesis are described as below: We proposed and verified theoretically the vacuum acceleration based on a new setup of applied electromagnetic (EM) fields. This setup contains two crossing laser beams whose propagation directions are vertical mutually and phases are spaced by a shift π/2. Strict theory and numerical results reveal that, under a given total EM energy density, such a crossing-beams case is more effective to accelerate charged particle than single-beam case. The maximum energy an electron can achieve in the crossing-beams case is about tens times of that in the single-beam case. Reasonable explanation on this phenomenon is also given. We developed vacuum acceleration based on multiple stimuli setup which is represented by above-mentioned crossing-beams setup, and study a new setup which is achieved by replacing a laser beam in the crossing-beams configuration with a static electric field. Such a setup can lead to electronic motion being non-time-periodic (or a mixture of time-periodic and time-monotonic behavior). Such a mixed motion corresponds to a realistic increment of kinetic energy. Under same total EM energy density, the maximum energy an electron can achieve in this setup is far larger than that in the single-laser-beam setup. We proposed a non-perturbation theory on the vacuum acceleration based on another varied version of previously-mentioned two-crossing-laser-beams setup. In this new setup, one of two laser beams is replaced by a static magnetic field. Strict theory and numerical results reveal that electronic motion is a mixture of time-periodic and time-monotonic behavior. Under same total EM energy density, the maximum energy an electron can achieve in this setup is far larger than that in the single-laser-beam setup. We proposed and verified theoretically that a setup in which a static electric field and a static magnetic field are applied along two vertical directions can effectively cut down the size of a conventional solid-state accelerator. Strict theory and numerical results reveals that such a setup can cause high-velocity electron to make a 180 degree deflection within a very small sized space region, whose size is several orders of magnitude lower than that required for a conventional deflection completely caused by magnetic field. This fundamentally warrants a table-sized conventional solid-state accelerator without being constrained by huge-sized bending region. We propose strict solution of the transverse shape of a light beam in vacuum. Because of finite-valued light power, how to distribute EM energy within the transverse section of the beam is a worthy question. In conventional Optics theories, this question is treated by approximations such as Paraxial-approximation or slowly-varing-envelope-approximation. Although these approximations can yield various transverse inhomogeneous intensity profiles (or shape), the accuracy of these solved profiles are uncertain (because they are based on approximations.) Our strict theory reveals how to seek strict (rather than approximated) transverse inhomogeneous solutions of wave equation with reasonable transverse boundary conditions. This is very important to exactly predict laser-matter interaction. Based on such a strict transverse inhomogeneous solution, we verified theoretically the feasibility of vacuum acceleration by single laser beam. We find strict macroscopic equation set on self-consistent fields of charged particle system. The acknowledged Vlasov-Maxwell equation set, which is on macroscopic self-consistent fields and microscopic distribution function, is very difficult to be calculated under realistic 6D case. Even for PIC simulation which is the most reasonable treatment on the Vlasov-Maxwell equation set, it is still difficult to make a long-time-scale and large-space-scale prediction (because updating macroparticles’ information is too time-consuming). We derived strictly, from different start points, an exact closed equation set which does not involve microscopic distribution function. This enables us to make a fast and exact long-time-scale and large-space-scale prediction on the self-consistent fields. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15899]  |
| 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 | 林海. 真空加速的优化及相关问题研究[D]. 中国科学院上海光学精密机械研究所. 2015. |
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