A High-Gain ${X}$ -Band Overmoded Relativistic Klystron

A high-gain X-band overmoded relativistic klystron is presented in this paper. The device mainly consists of an input cavity, two buncher cavities, and an output cavity. Moreover, two reflectors are added before and after the input cavity, therefore a standing wave is formed between the two reflectors, improving the initial modulation of the electron beam. With two sectional RF lossy materials inserted, the input cavity and the two buncher cavities are effectively isolated with each other. An additional reflector located just before the output cavity further reflects the backward-flowing power. Particle-in-cell simulations show that for a 10-kW injected microwave with a frequency of 9.37 GHz, the generated microwave power is 1.2 GW, corresponding to a beam-wave interaction efficiency of 30% and a gain of 50.8 dB. As the injected power increases from 10 to 100 kW, the frequency control range extends from 30 to 130 MHz.