Dynamics of electron beam instability development in short-pulse system for microwave generation

Summary form only given. Dynamics of instability development is an important characteristic of any system. Depend on needed length of radiation pulse, the operating substance in microwave devices is long continuous beam or series of short electron bunches. Propagation of a series of short electron bunches fundamentally differs from propagation of continuous beam. The difference is that every bunch´s front induces electromagnetic fields. Namely these fields provide the space charge and self magnetic field neutralization. From the other side these fields interact resonantly with the beam electrons and this interaction results in the beam instability development. Actually these fields serve as an initial perturbation for instability development. They increase exponentially and may significantly influence on many aspects of the physics of the system. These fields actually form transient processes in microwave devices. The time necessary to attain the operation regime critically depends on the dynamics of these fields. These fields also effects on process of electron bunching and phase-focusing in microwave sources. The development of the fields induced by beam front in turn relates directly to the character of instability evolution. In system with short electron bunches back edges induce fields of opposite sign, and they, by part, neutralize fields from front edge. As a result complicated structure establishes depend on bunch length, distance between bunches, and character of instability development. In present investigation development of conventional beam-plasma instability in systems penetrated by series of short electron bunches is considered. Approach enables to single out the most intrinsic peculiarities of induced fields´ behavior in considered system. It is shown that the fields induced by bunches´ edges serve as an initial perturbations for development of conventional beam instability. The effect of front and back edge of the bunch results in complicated co- figuration of the induced fields.