Influence of High-Frequency Characteristic of a Cavity on the Phase Shift in the Relativistic Klystron Amplifier

The influences of the eigenfrequency and the intrinsic quality factor of a cavity on the phase shift in the relativistic klystron amplifier (RKA) are investigated. An analytical expression is derived to describe the phase of the gap voltage in a cavity. The theoretical and simulation results indicate that the eigenfrequency of the buncher cavity can significantly affect the phase shift of the output microwave in the RKA. In contrast, the influences of the eigenfrequency and the intrinsic quality factor of the output cavity on the phase shift of the RKA are small. The analytical expression can effectively estimate the phase difference among different RKAs resulting from the machining and assemblage inconformity in the experiment. It is suggested that the differences among the eigenfrequencies of the buncher cavities should be managed in 0.1% of the operation frequency to achieve phase locking among different RKAs.