Plasma emission sources for intense electron beams

Various sources are being used for generation of high-current electron beams (current amplitude of 10³–10⁷A, electron energy of 10⁴–10⁷eV and pulse duration of 10⁻⁹–10⁻⁵s) in specially designed diodes. The main requirements for these sources are as follows: (a) electron emission occurs simultaneously with the accelerating pulse; (b) the extracted electron current density should be governed by the space-charge law; (c) the extracted electron current density should be uniform in its cross-section; (d) the electron source should have a long lifetime (≥10⁶ pulses) and it has to be reliable and reproducible; (e) the electron source should be compatible for operation in vacuum of 10⁻⁴–10⁻⁸Torr. One can divide electron sources into passive and active ones. By passive sources we consider sources which emit electrons under the application of an accelerating pulse. By active sources we consider sources of plasma that can be produced by various methods prior to the application of the accelerating pulse. In this review we consider different types of passive cathodes operating at E≤10⁵V/cm and active plasma sources based on ferroelectric cathodes.