The use of SEM to investigate the effect of an electron beam on the optically-visible flashover treeing of MgO ceramic
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This paper introduces the use of a scanning electron microscope (SEM) to evaluate the insulation property of insulators under electron bombardment. An SEM may be used not only to observe a surface image but also to provide a fine electron beam for charging an insulator surface simultaneously. The distribution of electric field created by the surface charging can be developed by a simple model. The increase of electric field at the surface may exceed a critical value to experience a surface breakdown/optically-visible flashover. The insulation property is evaluated by measuring the period of charging/electron bombardment, which is needed to initiate a treeing-formation (hereinafter time to flashover treeing/TTF). In this paper, under a 25 keV primary electron beam energy and for a magnification of 5000×, a 99.95% purity polycrystalline MgO specimen resulted in 7 min TTF. It was also observed that increasing the primary beam energy and the SEM’s magnification decreased the TTF. Therefore, at for a given energy and magnification, this method can be used to evaluate the insulation property of insulators under an electron beam environment.
KeywordsElectron Beam Energy Emission Current Density Incident Electron Beam Primary Beam Energy Scanning Electron Microscope Vacuum
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