Relaxation of Electric Field by Covering Cathode Edge With Vanadate Glass

The surface flashover discharge model under direct current (dc) voltage in a vacuum is considered an avalanche discharge induced according to the field emission electrons generated by the electric field concentration and secondary electron yield on the insulator surface. One of the effective ways to suppress this phenomenon is to suppress the field emission electrons at the origin. We have investigated a method for relaxing the field concentration by covering the cathode edge with metallic glass, and the following conclusions were obtained. Metallic glasses are conductive dielectrics and can be sintered to form amorphous and smooth surfaces. Covering the cathode surface with metallic glass is expected to relax the electric field concentration around the cathode edge. The metallic glass evaluated was vanadium-based, with a glass transition temperature of 321 °C, a crystallization temperature of 439 °C, a resistivity of 107–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{8}~\Omega $ </tex-math></inline-formula>-cm, and a relative permittivity of 15. The withstand voltage of a sample with a cathode and an anode formed on an alumina surface was evaluated with and without a metallic glass coating on the cathode edge. As a result, the voltage holding capability was approximately 2.7 times higher than without the coating, under an ultrahigh vacuum of 10−7 Pa, and a good electric field relaxation effect was obtained. The numerical simulation of the electric field concentration relaxation effect of metallic glass as a conductive dielectric material showed that the relaxation effect was equivalent to the experimental results. Future applications will include practical applications such as pin-to-pin interaction in multipin feedthroughs.