Chinese Acad Sci, Inst High Energy Phys, Beijing 100080, Peoples R China
; Univ Elect Sci & Technol China, Inst High Energy Elect, Chengdu 610054, Peoples R China
FEM amplifier with a novel groove waveguide and helical wiggler is proposed and researched both in three-dimensional nonlinear theory and numerical computation in this paper. A set of equations about this model is derived. Efficiency and bandwidth of the FEM are studied including the electron beam emittance effect on it.