On the phenomenon of a plasma-loaded high-power backward wave oscillator

Summary form only given. Recently it has been demonstrated that the presence of a low density background plasma in a slow wave structure (SWS) of a backward wave oscillator (BWO) can lead to a sufficient enhancement in output power. There exist several treatments of this effect at present, but it appears that full clarity has not been achieved yet. We would like to point out one effect which may be important in this regard but has not been analyzed yet. It is well-known that BWO output power is strongly sensitive to variation of the cavity length, i.e. to the mutual placement of a synchronous point frequency and nearest eigenfrequency of SWS. The presence of plasma changes the optical length of SWS and shifts its eigenfrequencies. Therefore it can cause an increase in the output power. To examine the role of this effect an accurate computer simulation of finite-length plasma-filled BWO has been performed using the singular integral equation method which takes into account the "full wave" solution for electromagnetic fields and self-consistent mode coupling at the output and input ends of the SWS within the scope of the linear beam model. The results obtained indicate that the periodic output power dependence on plasma density is similar to that obtained in experiment.