Study On Nonlinear Characteristics Of FEL At Millimeter Wave Band

Nowadays, millimeter wave band free-electron laser(FEM) is an important branch of free-electron lasers. Considering the potential application of FEM in new generation radar in the future, 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 FEM amplifier is researched in detail. A set of coupled nonlinear differential equations of the FEM amplifier which can be applied to both Rarnan regime and high-gain Compton regime of operations is derived in three dimensions. Based on these equations, a numerical simulation program, R-FEL3D, is developed independently, which includes the effects of electron momentum spread, mode competition, space charge effects, wiggler taper and so on. This program is tested strictly and proved to be credible. It is a valuable CAD(Computer Aided Design) tool for developing FEM amplifier in our country. By means of R-FEL3D simulation program, the nonlinear evolution of a free-electron laser (FEL) 35-GHz amplifier is investigated for a configuration in which an electron beam propagates through an multi-mode rectangular waveguide in the presence of a planar wiggler with paraboloidal tapered pole pieces. It is found that comparison with a single-mode analysis the enhancement of the efficiency of the lEo5 mode obtained by means of a tapered wiggler is significantly greater when the TE21 and TM21 modes are included in the simulation. The theory and simulation is found to be good agreement with the experiment performed by Orzechowski and co-workers[Phys. Rev. Lefl. 54, 889(1985); 57, 2172(1986)] By means of R-FEL3D simulation program, a rectangular waveguide FEM amplifier operating in 94GHz is researched in detail. The theoretical analysis and numerical simulation show this kind of FEM amplifier wih rectangular waveguide and planar wiggler is able to used as power source of the new generation millimeter wave radar. Taking the current technology levels into consideration, a feasible FEM amplifier scheme applied to the new generation radar is presented and the main parameters are given.