Emission uniformity and emission area of explosive field emission cathodes

Explosive field emission cathodes have been used extensively in high power microwave tubes. These cathodes emit electrons without the use of cathode h eaters. Recently, some theoretical and simulation work has been performed t o gain further understanding of the physics of these cathodes. The purpose of this letter is to provide the experimental background and justification for the theoretical work. The general idea of how explosive field emission cathodes operate is that plasma is rapidly formed, which provides the sea o f electrons for space charge limited flow. However, recent theoretical and experimental work suggests edge effects, rather than plasma formation acros s the entire emission area, can also provide the same effect. In this lette r we review three types of cathodes which have been tested. We provide opti cal data on the cathode emission uniformity as well as the electrical data for the same devices. In particular, we find that a large percentage of the cathode can fail to take part in the emission process and yet the voltage and current can appear identical from the case in which the entire cathode contributes electrons to the emission process. (C) 2001 American Institute of Physics.