STUDIES OF THE INITIATION OF ELECTRICAL BREAK DOWN IN VACUUM
NAVAL RESEARCH LAB WASHINGTON DC
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It is generally known that an applied field of 100000 vcm will produce electron emission from apparently smooth surfaces at room temperature. This pre breakdown current is believed to initiate electrical breakdown in vacuum. Experimentally it has been found that this pre breakdown emission is independent of emitter temperature up to 800C. By using electron-shadow- microscope techniques, projections about two microns high, capable of producing field enhancements of the order of 100, have been found on optically polished cathodes at prebreakdown emission sites. This, with other evidence, strongly indicates that prebreak down emission is Fowler-Nordheim field emission, due to geometrical field enhancement.
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