Comparative research on three types of coaxial slow wave structures

This paper studies three types of coaxial slow wave structures (SWSs): (1) with ripples on both the inner and outer conductors; (2) with ripples on the outer conductor and smooth on the inner one; and (3) with ripples on the inner conductor and smooth on the outer one. The frequencies, coupling impedances, time growth rates and beam-wave interaction efficiencies of the three types of coaxial SWSs are obtained by theoretical analysis. Moreover, the relativistic Cerenkov generators (RCGs) with the three types of coaxial SWSs are simulated with a fully electromagnetic particle-in-cell code, and the results verify the theoretical analysis. It is proved that the RCG with double-rippled coaxial SWS has the highest conversion efficiency and the shortest starting time.