Characterization Of A Space Charge Limited Non Relativistic Electron Beam Diode Operating At 300 KV/cm

High current density (>100 A/cm/sup 2/) electron beam diodes operating beyond 250 kV/cm in a 1-cm gap configuration are described. The principal features of the electron source are the high current density and high field gradient without the onset of vacuum arcs or arc collapse prior to gap closure. The electron beam diode was controlled by a variable pulse-width output Marx generator. Fields of up to 600 kV/cm were applied for 25 to 30 nsec, and up to 300 kV/cm during space--charge limited current conduction at pulse lengths of 100 to 120 nsec. Evidence of the transition to space-charge limited unipolar flow and transition to bipolar space--charge limited flow was obtained. Estimation of plasma closure velocity were made from several gap closure events and perveance plotting. Traces of the typical behavior and the different transitions shown. Beam uniformity was measured by using a set of Faraday cups. The Faraday cup set-up was then used to demonstrate suppression of electron emission from surfaces coated with a dielectric film.