【作者】 茅倾青；

【导师】 孔青；

【作者基本信息】 复旦大学 ， 原子与分子物理， 2008， 硕士

【摘要】 随着强激光技术的飞速发展,利用激光的超强电磁场加速带电粒子,并据此发展新一代小型化高能电子加速器的相关研究受到了人们的普遍关注。在之前对于激光加速电子的研究中,电子的辐射反作用效应一般都是被忽略的。然而在超强激光作用下,电子的辐射是否会对加速效果产生较大影响是需要仔细考虑的。本文致力于探讨激光加速电子中的辐射反作用效应对电子动力学和加速效果的影响。本论文首先讨论了辐射反作用问题的描述和计算方法。我们首先考察了经典的非相对论情况,给出了辐射反作用力的计算公式,并说明了经典辐射反作用力计算公式所面临的问题和局限性。然后讨论了将辐射反作用的计算推广到相对论条件下的洛伦兹—狄拉克(Lorentz-Dirac)方程,并给出了实用的计算辐射反作用力的微扰展开式。在此基础上,我们采用了预测—修正(Predictor-Corrector)算法,建立了模拟计及辐射反作用的激光加速电子过程的三维数值模拟程序。通过三维数值模拟,我们首先比较研究了在有质动力加速(PAS：Ponderomotive Acceleration Scenario)过程中,忽略辐射反作用效应和不忽略辐射反作用效应的电子动力学的差异。我们发现对于PAS过程,辐射反作用对电子动力学的影响是非常小的、可以被忽略的。在计及辐射反作用效应后,部分电子的最终出射能量比忽略辐射反作用效应的反而要大一些。然而这种能量的增大相比于我们的计算精度来说也是很小的,这一效应是可以忽略的。我们进而研究了电子俘获加速(CAS:Capture and Acceleration Scenario)过程中辐射反作用的影响,发现对于一般的CAS过程,辐射反作用的影响也是非常小的。随着激光强度的不断上升,由于辐射引起的电子的能量损失的确会逐渐增大,然而即使是a0接近500的超强激光,辐射反作用的影响也是极其有限的。最后通过对辐射反作用力表达式中的各分项的分析,我们给出了不同的计算辐射反作用力的经典方法的适用范围。这项工作对于激光电子加速的研究是个很重要的补充。我们的另一项工作是,针对CAS验证实验设计所面临的困难,提出了一种新型的CAS电子注入器的设计方案。我们设想可以从激光系统中分束出一束激光,使用激光等离子体尾场加速机制产生近单能的电子束团作为CAS加速的入射电子束团。这一方案可以不需要额外的加速器并能解决电子束团和激光脉冲的时间同步问题。通过PIC数值模拟我们在一定条件下得到了能量约20MeV的近单能的电子束团,我们分析了束团特性,并对其不足进行了讨论。另外我们还首次给出了TEM(1,0)+TEM(0,1)模激光在等离子体中激发的尾场的特性。这项工作对于CAS的实验设计有着重要意义。更多还原

【Abstract】 With the rapid development of laser technology, there has been growing research interest concerning the acceleration of charged particles by intensive electromagnetic fields of laser, and the design of modern high-energy and miniaturized accelerators. In the former studies on laser electron acceleration, the radiative reaction effect of electrons is always ignored. But when electrons are interacting with the super strong laser field, we have to carefully consider whether the radiation of the electrons will greatly affect the efficiency of acceleration. In this thesis, we discuss the radiative reaction effect on electron dynamics and acceleration efficiency in laser electron acceleration.This thesis begins with how to describe and calculate the radiative reaction. First, we investigate the expression of radiative reaction force in the classical non-relativistic regime, and explain the limitation of this expression. Then we discuss the generalization of the radiative reaction in relativistic regime, the Lorentz-Dirac equation, and give an expression of radiative reaction force by using small perturbation expansion. Using Predictor-Corrector method, we establish a three-dimension numerical simulation program to simulate the laser electron acceleration progress including radiative reaction effect.By using the three-dimension numerical simulation, we compare the electron dynamics with and without the radiative reaction in PAS (Ponderomotive Acceleration Scenario). We find the radiative reaction takes only a little effect on electron dynamics and can be ignored. When the radiative reaction is included, the final energy of some electrons can be a little greater. But this increment is very small even compared to our computing precision. So this effect can be ignored.We proceed to study the radiative reaction effect in CAS (Capture and Acceleration Scenario), and find the radiative reaction effect is also very small. With the increase of laser intensity, electrons do lose more energy by radiation. But even when a0 is close to 500, the radiative reaction effect is still limited. At last, we analyze each term in the expression of radiative reaction force, and we give the applicability of different classical methods of radiative reaction calculation. This work is a very important complement to the research of laser electron acceleration.Another work done by us is that we raise a new design of electron injector to solve the difficulties in CAS validation experiment. We assume that we can use a part of laser energy from the main laser system and use laser plasma wakefield acceleration to produce quasi-monoenergetic electron bunch. By using this design, we do not need additional accelerator, and we can control the synchronization between the electron bunch and laser pulse much more easily. Under some condition and parameters, we obtain the quasi-monoenergetic electron bunch of about 20MeV by using PIC simulation method. We analyze the character of the bunch, and discuss the shortage. In addition, we firstly give out the character of plasma wakefield produced by TEM(1,0)+TEM(O,1) mode laser. This work is very important to the design of CAS experiment.更多还原