Pulsed Plasma Electron Sources

Pulsed ($\sim $10$^{-7}$ s) electron beams with high current density ($>$10$^{2}$ A/cm$^{2})$ are generated in diodes with electric field of $E >$ 10$^{6}$ V/cm. The source of electrons in these diodes is explosive emission plasma, which limits pulse duration; in the case $E <$ 10$^{5}$ V/cm this plasma is not uniform and there is a time delay in its formation. Thus, there is a continuous interest in research of electron sources which can be used for generation of uniform electron beams produced at $E \le $ 10$^{5}$ V/cm. In the present report, several types of plasma electron source (PES) will be considered. The first type of PES is fiber-based cathodes, with and without CsI coating. The operation of these cathodes is governed by the formation of the flashover plasma\footnote{Ya. E. Krasik, J. Z. Gleizer, D. Yarmolich, A. Krokhmal, V. Ts. Gurovich, S.Efimov, J. Felsteiner V. Bernshtam, and Yu. M. Saveliev, J. Appl. Phys. \textbf{98}, 093308 (2005).} which serves as a source of electrons. The second type of PES is the ferroelectric plasma source (FPS).\footnote{Ya. E. Krasik, A. Dunaevsky, and J. Felsteiner, Phys. Plasmas \textbf{8}, 2466 (2001).} The operation of FPS, characterized by the formation of dense surface flashover plasma is accompanied also by the generation of fast microparticles and energetic neutrals.\footnote{D. Yarmolich, V. Vekselman, V. Tz. Gurovich, and Ya. E. Krasik, Phys. Rev. Lett. \textbf{100}, 075004 (2008).} The latter was explained by Coulomb micro-explosions of the ferroelectric surface due to an large time-varying electric field at the front of the expanding plasma. A short review of recent achievements in the operation of a multi-FPS-assisted hollow anode to generate a large area electron beam will be presented as well. Finally, parameters of the plasma produced by a multi-capillary cathode with FPS and velvet igniters\footnote{J. Z. Gleizer, Y. Hadas and Ya. E. Krasik, Europhysics Lett. \textbf{82}, 55001 (2008).} will be discussed.