Effects of plasma filling on microwave emission in a BWO with non-uniform slow wave structure

Abstract

Summary form only given. In a backward wave oscillator (BWO), an electron beam flowing in a waveguide interacts with a ripple in the waveguide wall, known as a slow wave structure (SWS), to produce high power microwaves. The introduction of either a non-uniform ripple or plasma filling in the waveguide has been shown to increase the output power of the BWO. The effect of a non-uniform ripple and plasma filling is studied using the computer code MAGIC. For a BWO with a non-uniform SWS geometry similar to that used in experiments at UNM, the effects of plasma density, plasma radius, and the amount of plasma filling on microwave emission are being simulated. Preliminary results suggest that higher power is produced only with a plasma density less than the electron beam density. In addition, our MAGIC simulations are testing the prediction made by an analytical study which suggests that higher output power will be generated with a plasma concentrated within a small radius and an annular electron beam flowing at a larger radius close to the SWS ripples. The effects of the amount of plasma filling are also studied to determine if the presence of plasma beyond the SWS inhibits the production of high power microwaves in a plasma filled BWO.