Improving withstand voltage by roughening the surface of an insulating spacer used in vacuum

TLDR

The study proposes a simple, reliable method to enhance the surface insulation strength of vacuum spacers. The method involves roughening the spacer surface to an average roughness above 1–2 µm, using materials such as SiO₂, PMMA, PTFE, or Al₂O₃ in a right‑cylindrical shape, and measuring surface charging under ramped DC voltage with an embedded electrostatic probe. Higher surface roughness reduces charging, and when the roughness exceeds ~2 µm the charging is suppressed until a higher voltage is reached, thereby improving insulation.

Abstract

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/sub a/ higher than 1 or 2 /spl mu/m. The material of the spacer examined is SiO/sub 2/, PMMA, PTFE or Al/sub 2/O/sub 3/ and their shape is a right cylinder with 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/sub a/ decisively affects the charging, which decreases as R/sub a/ increases. Increasing R/sub a/ larger than about 2 /spl mu/m suppresses the charging until a higher applied voltage is reached, thus improving the insulation property.