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

在这项研究工作中，我们对高亮度电子束和自由电子激光(FEL)振荡进行了数值模拟，采用了时域有限差分法(FDTD)作为麦克斯韦方程的解算器。首先，对热离子射频枪的束流特性进行了FDTD模拟研究。工作结果改进了实际射频炮的设计工作。在第二年，利用FDTD模拟结果对束团压缩的束流光学结构进行了优化，发现有可能在70飞秒左右产生很短的电子束团长度。此外，从理论上研究了太赫兹区相干同步辐射的特性，设计了光源加速器的基本布局。随着模拟程序的发展，考虑了空间电荷的影响，精确地计算了束团压缩机中的束流动力学。指出了产生100飞秒束团的可能性及其在基于新型加速器的相干光源中的应用。同时，利用FDTD程序成功地模拟了低能量直流束对Smith-Purcell返波振荡器(BWO)自由电子激光器的激光作用。结果表明，Smith-Purcell BWO自由电子激光器需要具有小于1 mm mrad的归一化发射度和小于50keV的动能。该光源在未来的窄带强亚太赫兹辐射中是非常有前途和独特的。

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.