Design and Experimental Demonstration of a Long-Pulse, X-Band Triaxial Klystron Amplifier With an Asymmetric Input Cavity

A triaxial klystron amplifier (TKA) with an asymmetric input cavity is designed to generate a long-pulse high power microwave at X-band. The input microwave is equally divided into two parts and then injected into an asymmetric input cavity to keep the axial electric field azimuthally symmetric in the input cavity. An asymmetric mode competition resulting in a pulse shortening on the output power is observed in a TKA with an asymmetric input cavity. The analysis indicates that the asymmetric mode is excited and amplified in the buncher cavity for the coaxial waveguide cannot cut off the corresponding asymmetric TE mode. By a reflector with high reflection coefficients both to the asymmetric mode and the TEM mode, the asymmetric mode competition is effectively suppressed in 3-D particle-in-cell simulation. The designed TKA is demonstrated by the experiment, in which a microwave with pulse duration of 100 ns, a power of 240 MW, and a gain of $\sim 34$ dB is generated.