偏心电子注激励周期加载波导角向非对称模衍射辐射

Radiation from the unsymmetrical modes of the periodical waveguide structure excited by eccentric electron beam

周期加载波导中匀速带电粒子的衍射辐射是产生较高频段可调谐太赫兹电磁辐射(频率高于1 THz)的有效方法.对圆柱形周期加载波导中偏心电子注产生的衍射辐射现象,进行了严格的理论分析和粒子模拟验证.研究表明,偏心电子注在波导中除了激励起角向对称模(TM_0波)以外,还将激励起角向模式为1(HE_1波)和2(HE_2波)的角向非对称模.并且电子注偏离轴线距离越大,激励的角向非对称模场强越强.每个模式的功率随电子注的激励位置呈变态贝塞尔函数平方关系变化,与电子注电流平方成正比.理论分析与计算机模拟的结果符合较好.研究结果将为发展该类可调谐太赫兹辐射源提供理论依据.

The special kind of diffraction radiation from the uniformly moving electron beam in a periodical waveguide structure has great potential applications in developing the tunable terahertz radiation sources. Rigorous theoretical analyses and detailed computer simu- lation on the diffraction radiation from the periodical waveguide structure excited by the eccentric electron beam are carried out. Our results show that the eccentric beam can primarily excite the axial symmetrical modes （TM0 modes） and axial unsymmetrical modes with axial variation numbers of 1 and 2. The energies of the unsymmetrical modes increase with the distance of electron beam to the axis. For each mode, the radiation intensity changes with beam location as the square of modified Bessel function and in direct proportion with the square of the charge quantity. The results of theoretical analyses and computer simulations are in good agreement with each other. These results are of significance for developing this kind of radiation source.