Frequency and power response of high-power plasma-filled backward-wave oscillators

Backward-wave oscillators (BWO) have long been used as voltage-tunable sign al sources, and more recently as high-power microwave (HPM) sources. The fr equency at which a BWO oscillates is commonly viewed as being determined by the circuit geometry and the electron beam parameters. However, several te chniques used to improve the efficiency and reduce the size of HPM BWOs, su ch as the Pasotron, cause the frequency to vary in discrete steps with chan ges in the beam parameters, and a plasma in these device can cause the freq uency to chirp (increase significantly) during the pulse. End reflections i n low-loss circuit designs and excessive plasma generation in these new sou rce geometries produce nonclassical frequency and power behavior. (C) 1999 American Institute of Physics. [S1070-664X(99)01505-0].