Excitation and suppression of asymmetric modes in a coaxial relativistic klystron amplifier with cascaded single-gap bunching cavities

The excitation and suppression of asymmetric modes in a coaxial relativistic klystron amplifier (RKA) with cascaded single-gap bunching cavities are analyzed this paper. Through theoretical analysis simulated verification, we find that the have low external quality factors, same resonant frequencies, negative beam-loading conductance ratios so they easily excited by electron beam. To solve issue, feasible method is proposed paper to suppress cavities, under conditions decreasing their coupling coefficients increasing frequency separation, choosing an appropriate drift tube length between them. These improved further examined X-band RKA 3D particle-in-cell simulation, which shows high power microwaves 0.8 GW generated corresponding efficiency 40%. Furthermore, there no mode competition during 150 ns simulation time.