Design of an X-band high efficiency coaxial relativistic backward wave oscillator with permanent magnetic package

Relativistic backward wave oscillators (RBWOs) have the characteristics of high power and high repetition rate. Reducing the magnetic field strength and the weight of the external permanent magnet (PM) is a significant development direction of RBWOs. In previous research, an X-band RBWO enclosed with a PM has achieved a power efficiency of 50%. However, the PM used in these papers requires a magnetic field magnitude of over 0.68 T, which leads to a weight exceeding 400 kg. The RBWO designed in this paper operates in coaxial TM01 mode, and the radial distance between its cathode and the surface of the slow wave structures reaches 7 mm. Under the condition of a low magnetic field, this design can provide a wide electron beam channel to avoid the rubbing of the electron beam envelope on the inner and outer conductors. Particle-in-cell simulation results have demonstrated that this RBWO achieves an output microwave power of 3 GW with a power efficiency of 50% enclosed in a PM with a magnetic field strength of 0.43 T and a weight of 74 kg.