Improving Withstand Voltage by Roughening the Surface of an Insulating Spacer Used in Vacuum

This paper describes a simple and reliable method of improving the surface insulation strength of a spacer used in vacuum. The method is to roughen the spacer surface to an average roughness R higher than 1 or 2 m. The material of the spacer a examined is SiO , PMMA, PTFE or Al O and their shape is a right cylinder with 2 2 3 10 mm in height and 54 mm in diameter. The spacer is subjected to a ramped dc voltage and its surface charging is observed by using an electrostatic probe embedded in the cathode. It has been found that R decisively affects the charging, which a decreases as R increases. Increasing R larger than about 2 m suppresses the a a charging until a higher applied voltage is reached, thus improving the insulation property. Index Terms — Charging, flashover voltage, insulating spacer, roughness, vacuum.