Characterization of Commonly Used Cold Cathodes in Explosive Emission Diodes

The technology used for the intense relativistic electron beam production has advanced significantly and is wide spread in use for variety of pulsed power applications generating several mega-watts of beam power. The production of such intense electron beam begins from electron source. In various applications of intense pulsed electron beams such as microwave generation, free electron lasers (FEL´s) etc., good electron beam quality (i.e. low divergence and uniformity) is of prime importance. Also, one would like to extract as much as current possible from a given cathode. Considering these issues, experiments have been done on most commonly used cold cathodes (aluminum and graphite) for field enhanced explosive electron emission. Mainly the effect of cathode geometry (i.e. area of electron emission), cathode material and transparency of anode on extracted beam has been studied. Experimental investigations of planar explosive emission diode with different cathodes has been done using compact water line based pulsed power source, capable of delivering 300kV, 60kA and 30ns pulse to a matched load of 50. Practical observations are well described by simulating simple model for space charge limited current in the presence of expanding plasma on anode wall as well as cathode surface. With this study, we sought to better understand electron field emission/diffusion processes that impact cathode material its geometry and effect of anode transparency in space charge cloud formation in the axially symmetrical planar diode configuration