Dynamics of overlimiting electron beam instability in plasma-filled waveguide

Abstract

Summary form only given, as follows. Generators and amplifiers on high current relativistic electron beams are one of the most perspective sources of intense microwave pulses. As it has been demonstrated by present researches plasma filling of the operating space can dramatically improve their performance compared to vacuum devices. Fundamental aspects of this improvement are the neutralization of beam space charge as well as its magnetic field. Plasma filled systems can pass through more capable beams and the devices may operate by currents higher than vacuum devices. The beam current may even exceed the limiting vacuum current. If the latter is the case new physical phenomena appear. The influence of the fields of the beam space charge become very important and electron beam instability changes its physical nature. Now it is due not to induced radiation of the system's proper waves but either to aperiodical modulation of the beam density in medium with negative dielectrical constant or to excitation of the beam wave with negative energy. The change of the instability physical nature leads to changes on many aspects of the operation of microwave devices. The dynamics of the beam instability development changes substantially. The efficiency of energy transfer from beam to excited waves changes also. In the report the space-time dynamics of the instability of overlimiting beams in a plasma filled waveguide is investigated. An analytical expression for space-time distribution of the fields is obtained and analyzed. The maximal growth rate is proportional to the square root from the beam density. Actually it is nothing else than the growth rate in the peak of the growing wave train. The shape of the induced wave train is presented. Unlike the case of sublimiting beam the peak is in its middle.