Design of a high-efficiency S-band relativistic klystron oscillator under a low guiding magnetic field

A high-efficiency S-band relativistic klystron oscillator (RKO) under a low guiding magnetic field is proposed and investigated in detail in this paper. Two-stage segmented modulation is introduced to compensate for the poor coherence of the electron beam, allowing the electron beam to be deeply modulated even under a low guiding magnetic field. In the particle-in-cell simulation, the proposed RKO generates a microwave with an output power of 3.66 GW at 3.10 GHz under a guiding magnetic field of 0.7 T, corresponding to the power conversion efficiency of 41.3%. To substantiate the practical performance, an experimental validation of the proposed RKO is conducted. The RKO successfully generates a microwave with an output power of 3.02 GW at 3.08 GHz, achieving a power conversion efficiency of 32.2%, under a guiding magnetic field of 0.71 T. These findings confirm that the S-band high-power microwave source can work with high power conversion efficiency under a low guiding magnetic field.