开放谐振腔SP FEL中电子注与高频场互作用的粒子模拟研究

【作者】 林娟；

【导师】 魏彦玉；

【作者基本信息】 电子科技大学 ， 物理电子学， 2008， 硕士

【摘要】 Smith-Purcell自由电子激光简称SP FEL,是自由电子激光的一个重要分支。本文对Smith-Purcell效应和开放腔SP自由电子激光器件进行了比较深入、全面的研究,取得了一些有价值的研究成果。本文首先根据Smith-Purcell自由电子激光理论,对一种新型自由电子激光器的特性进行研究。特别讨论了Smith-Purcell效应振荡器,主要对电子运动方程以及注波互作用关系进行了分析。分析了开放式谐振腔的优点、光学谐振腔的衍射理论并且介绍了开放式谐振腔的稳定球面腔解。利用二维的粒子模拟方法,采用了在开放矩形腔内设置平板光栅的结构模拟出了Smith-Purcell辐射现象。利用单电子束团从光栅表面经过并在腔中设置多个不同角度的观察点,通过观察纵向磁场的等势图、腔内多点的谐振频率以及电子束团的动量空间分布图,来研究Smith-Purcell效应,以及SP辐射波和散射波的区别。当单电子束团从光栅表面经过时会激励SP辐射,SP辐射波的频率会随着角度的变化而变化,根据模拟结果得出的辐射频率与角度的变化曲线与根据Smith-Purcell辐射公式画出的理论曲线非常吻合。利用多个电子束团在光栅表面经过,通过观察纵向磁场的等势图,来研究SP超辐射现象。通过对模拟结果进行分析和总结,SP超辐射也就是SP辐射的二次与三次谐波,辐射波的输出角度也与Smith-Purcell辐射公式一致。设计三种不同的光栅结构(矩形、梯形、倒梯形),研究光栅形状对SP辐射和散射波辐射频率的影响。然后采用在圆筒腔内设置圆筒栅结构,采用与以上相同的方法,同样观察到了SP辐射波与散射波,以及SP超辐射。模拟结果同样与Smith-Purcell辐射公式非常吻合,也进一步证明了矩形结构的正确性。对新型的开放式的Smith-Purcell自由电子激光器进行了建模,并利用二维的粒子模拟方法对冷腔以及注波互作用进行研究。通过研究两种不同情况的谐振腔,包括设置角度输出口和不设置角度输出口的两种结构,设计并模拟了三种不同形状的光栅,给出了各种激光器的输出结果并做出比较分析。通过对模拟结果进行研究分析可得,采用倒梯形光栅,可以的到相对比较大的功率输出;采用梯形光栅结构,可以得到相对大的频率输出。加工各种结构自由电子激光的实验样管,进行冷腔实验,和模拟冷腔实验的结果进行对比,结果基本相符。经过模拟调试,设计出满意的Smith-Purcell自由电子激光器,得到高功率的3mm波段的微波输出,对实际器件热测提供了有效的数据。更多还原

【Abstract】 Smith-Purcell free electron laser shortened as SP FEL is an important branch of free electron laser. This paper presents a more deeply and comprehensive study of Smith-Purcell effect and the SP free-electron laser devices in an open resonator, and good results are achieved.In this paper, at first, according to the theory of quasi-optical resonator diffraction and Smith-Purcell free-electron laser, we discussed the characteristics of a new structure free-electron laser, which mainly includes analysis of the electron movement equation and beam-wave interaction, and also introduction of the stable solution of the spherical cavity.With the help of two-dimensional particle-in-cells simulation, we adopt a flat gating in an open rectangular cavity model to simulate the Smith-Purcell radiation. By setting multitude observe point and observing the bitmap of longitude magnetic field, the frequency of the observe point and space momentum distribution of the beam, simulation for a single bunch is carried out first, from which we can observe the process of generation of SP radiation and the evanescent wave, and find the difference of them. When the single bunch passes over the grating surface, the SP radiation will be inspired. The SP radiation frequency changes with the angle. According to simulation results, the curve that radiation frequency changes with the angle is familiar with the curve draw follow the SP theoretical formula. Then, by observing the bitmap of longitude magnetic field, we simulate a train of periodic bunch to demonstrate the properties of the super-radiant radiation, the output angle of second harmonic and third harmonic frequency are also following the theoretical formula. By changing the shape of the grating, we can achieve different evanescent wave frequency. A cylindrical grating structure is designed to research the SP radiation, too. We used the same method above and also get satisfied results which rectified the correctness of the above model.We suppose the new structure of the SP FEL in an open resonator. And the cold test and electron beam-wave interaction in such system is performed by a two dimensional particle-in-cell simulation. By supposing two different structure and changing the shape of grating, the output result of all kinds FEL is given and made analysis. The entity of laser is completed and the cold test is carried out. The results match the simulation results well. By debugging the parameter of the simulation structure, we can design more satisfied SP FEL, achieving 3mm wave output with high power.更多还原