Study On FEL Amplifier With Coaxial Waveguide

Free-electron lasers (FEL's) are attractive as tunable sources of high power, high frequency coherent radiation. Considering the potential applications of FEL in military and civil areas, many science and research institutes in the world have been doing research in this field and have obtained some important results.In this dissertation, the FEL amplifier with coaxial waveguide is researched in detail. A set of coupled nonlinear differential equations of the FEL amplifier based upon a coaxial hybrid wiggler, which can be applied to both Raman regime and high-gain Compton regime of operations is derived in three dimensions. Based on these equations, a numerical simulation program is developed independently, which includes the effects of electron momentum spread, space charge effects, wiggler taper and so on. This program is tested strictly and proved to be credible. It is a valuable CAD tool for developing FEL amplifier in our country.By means of simulation program, the nonlinear evolution of a free-electron laser (FEL) 15-GHz amplifier based upon a coaxial hybrid wiggler is investigated. Influence on saturation characteristic caused by electron momentum spread, space charge effects, and wiggler taper is studied. A feasible FEL amplifier scheme is presented and the main parameters are given. Taking the current technology levels into consideration, we found that comparison with lower voltages, a pleased result is gained. The design of input coupler for a Ku-band coaxial FEL amplifier is presented. Main parameters are given. Simulations of this coupler were performed using HFSS, and transmission coefficient is obtained. This scheme is helpful to design related devices. Several valuable and important results are achieved through research on coaxial FEL amplifier:1) Computer program on FEL simulation is developed independently with the characteristic such as convenience and simple operation. This software can be used toassist designing FEL.2) FEL amplifier with coaxial waveguide operating at Ku band wave is analyzed by theory and numerical simulation in detail. Some important effects are researched .The results are useful to developing FEL devices.3) The designing scheme of input coupler is presented with main parameters. Simulations of this coupler were performed using HFSS, and transmission coefficient is obtained.