Analytic investigation of the transit-time instability including intense space charge effects

Summary form only given, as follows. A circuit model is used to investigate the transit-time instability (TTI). Although it has been known since the 1930's, recent efforts to develop a High-Power microwave (HPM) source using the TTI have focused on using modern pulsed-power technology to create high current (10's of kAmp) beams to drive the source. It is well known that the space charge associated with intense beams can severely complicate the analysis of HPM devices. This circuit model clarifies the role of space charge in the transit-time instability. Application of the model to the Radial Acceletron, currently being investigated at Phillips Laboratory, yields an analytic expression of the starting condition for microwave oscillations. Numerical solution of the governing equations gives growth rates, saturation levels, and elucidates the saturation mechanism in the presence of space charge. These results are consistent with full Particle-in-Cell simulations of the device.