Improving Surface Flashover Voltages of Alumina Insulators by Applying Titanium Dioxide Coatings

Experimental results of the improvement in the surface flashover voltage of an alumina insulator in vacuum achieved by applying a TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> coating are reported. We used a needle with a sharp tip made of conductive diamond as a cathode to easily repeat the measurements. In each measurement run, the applied voltage was ramped up until discharge occurred. The obtained average surface-flashover voltages of alumina with and without TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> coating are −7.4 kV and −24.9 kV, respectively. This improvement is attributed to a lower secondary electron emission yield and a reduced electric field at the cathode triple junction, and a lower degree of surface charging.