Experimental studies of high power plasma filled backward wave oscillators

Summary form only given, as follows. It has previously been demonstrated that a plasma-loaded backward wave oscillator (BWO) powered by a relativistic electron beam can generate hundreds of megawatts of microwave radiation at high efficiency (about 40%). An experimental study of an 8.4-GHz BWO filled with an externally controlled background plasma was performed. It was found that the enhanced efficiency can be maintained even for large electron beam currents approaching the vacuum space-charge limiting current, and it is anticipated that this might hold even beyond the space-charge limiting current. A small frequency up-shift (a few percent) was detected for the plasma loaded BWO. A hydrogen flashover plasma gun was used, and its characteristics, including plasma density, drift velocity, and temperature, were investigated. Detailed studies of beam propagation in vacuum as well as in plasma loaded structures were performed. It appears that a slightly over-moded device will be needed for peak power handling capability of 5-10 GW