|Ph.D Thesis||Department of Physics|
|Supervisors:||Prof. Emeritus Felsteiner Joshua|
|Prof. Krasik Yakov|
This work is directed to experimental investigations of physical processes in different types of plasma electron sources which could be used for generation of high current electron beams under moderate accelerating electric fields (£ 105 V/cm). Processes of plasma formation, plasma parameters and parameters of generated electron beams were studied for active plasma sources (i.e. sources where the plasma formation occurs by the application of an additional driving pulse) and passive plasma sources (i.e. sources where the plasma formation is caused by the application of the accelerating electric field).
As active plasma sources, ferroelectric plasma cathodes were studied. The investigated passive plasma sources were based on either dielectric or carbon fibers and on metal-ceramic structures. Various types of electrical, optical, and spectroscopic diagnostics were used to study the dynamics of plasma formation, the behavior of the plasma density and temperature, the potential distribution in the planar diode, and the uniformity and the divergence of the extracted electron beam. It was shown that all of the studied plasma sources have the same origin of the plasma formation. The formation of the plasma occurs due to incomplete surface discharge. Based on the obtained experimental results, a qualitative model of the surface plasma formation and the operation of investigated plasma sources was developed.
It was demonstrated that all of the investigated plasma sources are able to generate large area uniform electron beams with current amplitude of 102 - 103 A, current density of 1-100 A/cm2, and pulse duration of 10-8-10-6 s, under accelerating electric fields in the range of 30-80 kV/cm. The ferroelectric plasma cathodes are able to generate low divergence electron beams at a repetition rate of several Hz without significant decrease of the emission properties and without significant vacuum deterioration. Successful operation of a high-power magnetron with a specially designed ferroelectric plasma cathode was demonstrated.
A novel phenomenon, namely high frequency modulation of an electron beam generated in a planar diode with a ferroelectric plasma cathode, was found. Parameters of the modulated beam and a qualitative model describing this novel phenomenon are presented.