Research of High Quality Electron Beam and THz-FEL Based on Numerical Simulation for Electromagnetic Fields Employing a 3-D FDTD Method

本文采用时域有限差分法（FDTD）作为麦克斯韦方程组求解器，对高亮度电子束和自由电子激光（FEL）的振荡进行了数值模拟研究。首先，通过时域有限差分法仿真研究了电子射频炮产生的光束特性。研究结果对实际射频炮的设计工作有一定的改进作用。第二年，利用时域有限差分模拟的结果对束压缩的光束光学进行了优化，发现有可能产生70飞秒左右的极短电子束长度。此外，对太赫兹区域相干同步辐射的特性进行了理论研究，并设计了光源加速器的基本布局。随着仿真程序的不断完善，考虑空间电荷的影响，对束束压缩机的束流动力学进行了精确的计算。指出了产生100飞秒束的可能性及其在新型加速器相干光源中的应用。同时，利用时域有限差分（FDTD）代码成功地模拟了Smith-Purcell后向波振荡器（BWO）自由电子激光器在低能量直流光束下的激光运动。研究发现，对于Smith-Purcell BWO FEL，要求直流光束的归一化发射度小于1mmmrad，动能小于50kev。该源在未来窄带强次太赫兹辐射中具有独特的应用前景。

In this research work, we have investigated concerning high-brilliant electron beam and free electron laser (FEL) oscillation by means of numerical simulation employing Finite Difference Time Domain (FDTD) method as a Maxwell's equations solver. As a first step, beam characteristics produced by a thernionic RF gun was studied by the FDTD simulation. Results of the work have improved design work of the actual RF gun. In the 2nd year, the beam optics for the bunch compression has been optimized by using results of the FDTD simulation, then it was found that there would be a possibility of producing very short electron bunch length around 70 femto-second. In addition, properties of coherent synchrotron radiation in Terahertz region were studied theoretically and a basic layout of light source accelerator has been designed. As the simulation code has been progressed, the beam dynamics in a bunch compressor was precisely evaluated by taking the effect of space charge into account. As the result the possibility of producing 100 femto-second beam bunch and its application for a new accelerator based coherent light source were pointed out.Meanwhile lasing of Smith-Purcell backward wave oscillator (BWO) FEL using a low energy DC beam was successfully simulated by using the FDTD code. It was found that the dc beam having the normalized emittance less than 1 mm mrad and the kinetic energy of less than 50 keV is required for Smith-Purcell BWO FEL. This source is concluded to be very promising and unique for future narrowband intense sub-Terahertz radiation.