Performance of S band four-cavity relativistic klystron amplifier

In a relativistic klystron amplifier (RKA), the idle cavity can increase the gain of the device, but the oscillation of nonworking modes will occur in the same time, and therefore the performance of RKA will be significantly decreased. We developed a four-cavity relativistic klystron on the basis of three-cavity relativistic klystron to study the mechanism of nonworking modes oscillation. A PIC particle simulation software was used to study the cold cavity structure, beam-microwave interaction and microwave extraction of output cavity. An input cavity with low interaction impedance and a ladder structured drift were adopted in the structure to avoid nonworking modes oscillation. By optimizing the output cavity gap, the returning electrons had been significantly reduced, and thus the oscillation of nonworking modes was not excited. Finally, the output microwave with a power of 3.7 GW, a gain of 56 dB, an efficiency of 22% and 1 dB bandwidth of 74 MHz were achieved in simulation with the discussed structure.