Origination of oscillation startup in RBWO from radiation of electrons

In this paper, the radiation of electrons during the oscillation startup in the relativistic backward wave oscillator (RBWO) is investigated theoretically. It is found that the initial power of an X-band RBWO is in level of 1 μW, and the output power reaches up to 1 GW in 6~16 ns. The theoretical results agree with particle-in-cell (PIC) results to some degree. The theoretical method can be used to analyze the radiation of the electron beam and microwave power of other RBWOs at the beginning of startup.