Self-bunching electron guns

This paper presents several new approaches for producing bunched electron beams. The need for higher power injectors and microwave sources for various applications has in turn created the need for higher emission current density electron guns with a means for bunching at the gum. Four different cathode/gun approaches are presented. The first three utilize external methods of bunching. They are based on: field emission, photoemission and ferroelectric emission. The fourth is based on secondary emission and utilizes self-bunching. The latter is emphasized in this presentation. This self-bunching electron gun produces naturally bunched electron beams with the use of microwave fields to generate secondary emission and multipacting of electrons. This type of electron gun is called the Micro-Pulse Gun (MPG). One wall of an RF cavity is made opaque to an input RF electric field but is partially transparent to electrons in order to extract the beam. FMT has studied using simulation codes the resonant bunching process which gives rise to high current densities (0.01-5 kA/cm/sup 2/), high charge bunches (up to 500 nC/bunch), and short pulses (1-100 ps) for frequencies from 1 to 12 GHz. The beam pulse width is nominally /spl sim/5% of the RF period. Experimental verification of self-bunching, cold electron emission, long life, and tolerance to contamination has been achieved. Measurements of current density, bunch length and lifetime are presented for the MPG.