Numerical Studies on an Efficient Coaxial Superradiant Relativistic Backward Wave Oscillator With Low Magnetic Field

An efficient coaxial superradiant relativistic backward wave oscillator (SR-RBWO) operating at a low magnetic field is proposed and studied. In such SR-RBWO, a coaxial slow wave structure (SWS) is used in the interaction region, the coaxial structure can realize the stable transmission of the intense relativistic electron beam (IREB) in a long interaction region by using the relatively low guiding magnetic field. The existence of an inner conductor can reduce the radial electric field near the cathode emission region, which can reduce radial expansion and improve the quality of IREB. According to the dispersion relations in the coaxial SWS region, when the radiation frequency remains unchanged, the power capacity can be improved by changing the radius of the inner conductor. The particle-in-cell (PIC) simulation results reveal that when this oscillator is applied with a low guiding magnetic field of 0.32 T and diode voltage of 268 kV, the SR pulse with an average power of 1.62 GW corresponding to power conversion efficiency of 140% can be obtained, and output a relatively pure TEM mode at a center frequency of 8.6 GHz.