An Efficient Klystron-Like Relativistic Backward Wave Oscillator With a Five-Period Slow-Wave Structure and a TM₀₂ Mode Extractor

A klystron-like relativistic backward wave oscillator (RBWO) with a five-period slow-wave structure (SWS) and a TM02 mode extractor is described in detail in this article. In the device, the five-period SWS downstream of the resonant reflector is introduced to further boost the beam bunching process generated by the reflector. By adjusting the drift tube length between the reflector and the five-period SWS, as well as by selecting the proper working mode in the SWS, the optimal bunching phase in the SWS is maintained with the maximum bunching depth of 145.4%. The TM02 mode extractor downstream of the SWS is used to extract the kinetic power from the highly bunched electron beam. Owing to its partial reflection to the outgoing microwave, the electric field strength in the TM02 mode extractor increases from 34 to 44 MV/m when compared with the conventional TM01 mode extractor. Moreover, for the TM02 mode extractor, the phase of the axial component of the electric field in the extractor shifts $\pi $ radians relative to the last cavity of the SWS, which means that the highly bunched beam transits from the bunching phase in the SWS to the conversion phase in the extractor suddenly. Accordingly, the TM02 mode extractor could convert the beam power to microwave power efficiently. Computer simulations of the device show that at the applied voltage of 650 kV, electron beam current of 13 kA, and magnetic field of 0.7 T, the RBWO produces an intense microwave power of 4.2 GW, a frequency of microwave oscillations of 2.38 GHz, and the maximum conversion efficiency about 50%.