Plasma induced efficiency enhancement studies on the UNM long pulse BWO

Summary form only given. Several studies conducted with high power backward wave oscillators (BWO´s) have shown that significant increases in output power and generation efficiency can be obtained when a plasma is injected into the slow-wave structure (SWS) of the device prior to operation. Recent theoretical analyses have suggested that the injected plasma should be confined closely to the axis of the device, while the electron beam driving it should be as close to the walls as possible. A comprehensive set of measurements is being performed using the University of New Mexico (UNM) Long-Pulse BWO to test these suggestions. The UNM Long-Pulse BWO utilizes a plasma source that is mounted within the cathode stalk in the diode region. This configuration allows the plasma to be injected into the SWS upstream of the interaction region. Detailed measurements have been made of both spatial and temporal variations in plasma density and distribution within the SWS for several guiding magnetic field strengths. These data have been correlated with output power, pulse width, and microwave frequency observed from the BWO. Results to date will be presented.