Influence of Surface Microstructures on Explosive Electron Emission Properties for Graphite Cathodes

In this paper, two kinds of graphite cathodes with different surface microstructures were prepared, and their emission properties were investigated. The correlation of surface microstructures of graphite cathodes and their emission properties is discussed in detail. Surface morphological microstructures of the graphite cathodes before and after emission testing were characterized using scanning electron microscopy, X-ray diffractometry, and laser Raman spectroscopy. It was found that natural flake (NF) graphite cathode has significantly higher current, shorter current delay time, and larger effective emission area than POCO graphite under identical testing conditions. Relatively better emission properties of the NF graphite are probably due to their high graphitization degree and large size of graphite microcrystallite. After emission for about 500 pulses, surfaces of the graphite cathodes were smoothened and edges of the graphite particles were blunted, implying that electrons generally emitted from the sharp edges of graphite particles on the graphite cathodes. Furthermore, graphite of larger particles in irregular shape and of higher graphitization degree has enhanced emission properties such as higher emission current and lower current delay time.