Design of a High-Power V-Band Klystron With Internal Coupling Multigap Cavity

In this article, the design study of a V-band klystron with an internal coupling cavity is presented. The effective characteristic impedance of the internal coupling cavity is approximately 25% higher than that of the external coupling cavity when both operate at
$\pi $
mode. A V-band RF circuit of 35% efficiency has been designed based on the proposed internal coupling cavity. An RF circuit based on single-gap resonators was designed first with the help of genetic algorithms (GAs). Then, a five-gap internal coupling cavity replaced the last several resonators to improve circuit bandwidth and efficiency. Simulation results have shown that the proposed internal coupling cavity can significantly improve the efficiency and bandwidth of an RF circuit based on single-gap resonators. Driven by a 60-kV and 9-A pencil beam, the designed RF circuit can achieve a peak power of 188.5 kW, a gain of 47.8 dB, and a 1-dB bandwidth of 180 MHz. The matching high compression ratio beam optics is also elaborated in this article.