ELECTRON-EMISSION FROM SLOW-WAVE STRUCTURE WALLS IN A LONG-PULSE, HIGH-POWER BACKWARD-WAVE OSCILLATOR

Pulse shortening is a phenomenon common among all long-pulse, electron -beam-driven high-power microwave sources, Although the electron beam driving the source may continue to propagate through the interaction r egion of the device for several microseconds or more, the duration of the emitted microwave pulse is typically no more than similar to 100 n s. Most explanations of this phenomenon put forth involve the introduc tion of plasma into the interaction region and/or the degradation of b eam quality. This paper describes experiments conducted on the Univers ity of New Mexico's Long-Pulse Backward Wave Oscillator (BWO) Experime nt which investigate the behavior of beam electrons in the slow-wave s tructure (SWS) during microwave generation, A current probe having a s mall aperture at a variable radius is placed within the SWS to monitor the beam current profile at different radii as a function of time, Re sults from these experiments reveal the appearance of electrons betwee n SWS ripples at times corresponding to the peaks of the microwave pul ses in separate experiments, A drop in the main beam current is observ ed shortly thereafter. The source of the electrons within the ripples is thought to be field emission or secondary electron emission from th e SWS walls or emission from plasmas generated there.