Simulation analysis of cold-test characteristics of pitch-tapered helical slow-wave structure

Based on the MAFIA simulation platform, the effects of helix pitch on dispersion, interaction impedance and attenuation characteristics are analyzed for an ultra-wide band(4~18 GHz) helical slow-wave structure. The rules of the cold-test characteristics changing with helix pitch are also studied and it turns out that, with increasing helix pitch, the phase velocity increases linearly, the interaction impedance changes nonlinearly and the attenuation constant decreases nonlinearly. At the same time, with the limitation of the synchronism between the electron beam and the electromagnetic wave, the change of pitch is small and therefore an approximate linear relation can be introduced. Based on these effects and rules, the linear interposition method is suggested to get the cold-test characte