Suppression of the Higher-Order Azimuthal Mode Competition in an X-Band Triaxial Klystron Amplifier With a Slotted Coaxial Waveguide

Suppression of the higher-order azimuthal mode competition is significant in the design of an X-band triaxial klystron amplifier (TKA), since coaxial waveguide cannot cut off the low-order coaxial TE modes. In this article, the generation mechanism of the higher-order azimuthal mode competition is analyzed, and a slotted coaxial waveguide is specially designed to suppress the coaxial TE81 mode leakage. The results show that the reflection coefficient of the slotted coaxial waveguide can be optimized over 99%, and the reflection coefficient is sensitive to the variation of the slot length rather than the aperture angle or the thickness of the inner conductor. The combination of two identical slotted coaxial waveguides staggered azimuthally can effectively reflect the arbitrary polarized coaxial TE81 mode. Together with the reflectors specially designed to suppress the coaxial TE61 mode leakage, all of the asymmetric TE modes' competitions are restrained in this device. In the 3-D particle-in-cell simulation, the pulse-shortening resulting from the coaxial TE81 mode leakage is successfully suppressed with the slotted coaxial waveguide. The output power of the TKA achieves 1.28 GW, and the efficiency and gain are 34.5% and 41.5 dB, respectively. The slotted coaxial waveguide together with the reflectors eliminates the utilization of attenuation materials.