Oscillation-Starting Conditions for Oversized $G$ -Band (140–220 GHz) Backward Wave Oscillator Driven by Weakly Relativistic Electron Beam

An oversized G-band backward wave oscillator (BWO) driven by a weakly relativistic electron beam less than 100 kV is studied. Rectangular corrugations are used as the slow-wave structure (SWS), which have surface waves with upper cutoff frequencies of above 150 GHz [G-band (140-220 GHz)]. In this paper, we examine the starting conditions for intense G-band BWO operation by varying the beam parameters and SWS lengths. It is shown that a starting energy exists for the G-band BWO and that the starting energy is more critical than the starting current in the oversized BWO. Above the starting energy, very intense output powers on the order of 10 kW are obtained. The oscillation-starting condition for such intense operation may play an important role in high-intensity terahertz wave sources.