Electrostatic potential distribution characteristics of glass surfaces in vacuums

The voltage of vacuum-insulated high-voltage systems typified by X-ray tubes has recently increased. In particular, the surface discharge on the insulation material surface in a vacuum is a major problem. Recent studies show that the electrostatic charge of the insulation material surface is closely related to surface discharge. Therefore, we developed a measurement system that measures the electrostatic potential distribution of an insulation material surface with a scanning electrostatic voltmeter in a vacuum. We used this system to measure the electrostatic potential distribution of the surface of a borosilicate glass plate energized with a high voltage. A local increase in the electric field was observed. This phenomenon is caused by a positive electrostatic charge generated by a secondary emission of field emission electrons from an electrode. On the other hand, a local increase in the electric field was not observed on a glass plate coated with silica particles and a glass plate roughened by sandblast. We reasoned that this could be because the electrons were trapped by the roughness of the surface. In this paper, an outline of the measurement system, experimental results, and a discussion are reported.