Beam-plasma interaction in presence of dissipation in finite external magnetic field

Abstract

Summary form only given. Plasma-filled microwave sources on relativistic electron beams have essential advantages as compared to vacuum ones. Their operation is based on stimulated emission of the oscillations of plasma-filled waveguide by the beam electrons. They operate at higher beam current and the output frequency might be gradually changed by changing plasma density. With increase in beam current the character of the beam-plasma interaction (BPI) changes. Up to now theory of plasma- filled microwave devices is developed mainly in strong external longitudinal magnetic field. Such approach substantially simplifies the analysis. However, its applicability conditions may be violated in real experiments especially in short wavelength range. Description of devices based on cyclotron emission from beam electrons (i.e. based on anomalous Doppler effect) is impossible at all. There is a necessity in theory of microwave devices in finite external magnetic field. Now specific problems of this theory are begun to be considered. Plasma-filled microwave devices correspond to cylindrical waveguide with thin annular plasma and spatially separated coaxial thin annular e-beam. Along with maximal exhibition of the advantages of plasma filling this configuration provides development of beam instability (BI) caused by growth of negative energy beam wave (NEBW). Its growth rate attains maximum under collective (instead of usual) Cherenkov resonance. In these conditions the role of dissipation increases as it also leads to growth of NEBW. The trends of increasing output frequency leads to decreasing of the skin depth in the walls of resonators. Their quality factor Q decreases and actually dissipation increases. With increase in level of dissipation the BI becomes of dissipative type. In the configuration of microwave devices even small dissipation leads to a new type of dissipative BI with inverse proportional dependence on dissipation. Its properties and conditions of development are important additional factors that should be taken into account upon design of the devices. Present investigation substantiates the new type dissipative beam instabilities in finite external longitudinal field. It is shown that the new type of dissipative beam instability, presented in, develops also in finite external magnetic field and can essentially influence on operation of the devices.