“Much ado about nothing”: Electron sources and transport in vacuum

How electron emission is generated from photo, secondary, field and thermionic sources affects their vacuum transport characteristics and therefore their utility for differing Vacuum Electronic applications. Complications associated with emission processes will be related to desirable features of the beams produced in terms of current density, lifetime, space charge, beam halo, emittance, and response time, as well as limitations imposed by the emission mechanisms.