Particle simulation of relativistic klystron amplifier double-gap output cavity

Using a three-dimension fully electromagnetic particle-in-cell(PIC) code, double-gap output cavity of the S-band Relativistic Klystron Amplifier is simulated numerically. It is found that the microwave extraction power and efficiency is increased by employing the double-gap output cavity to change the distance of beam-microwave interaction. The relations between output power and depth of the modulated current and that between output power and r-distance of coupler hole, as well as the relation between output power and distance that electron beams is close to drifting wall are obtained. Furthermore, the relation between output power and DC transitional angle is presented and it accords with that of the theory. An 800 MW averaged power over the oscillator period is generated by simulation, w