Micro-effects of surface polishing treatment on microscopic field enhancement and long vacuum gap breakdown

In this paper, three surface polishing treatments were employed to treat plate titanium electrodes, and microscopic surfaces of the electrodes after polishing were presented. Through comparing the breakdown strength of the 2.5 cm vacuum gap formed by plate titanium electrodes after the three treatments, experimental results showed that the breakdown strength was enhanced by 35% while the micro-surface roughness dropped from 3.5μm to 0.35μm. In view of that, effects of microstructural parameters after polishing on the microscopic field enhancement factor were investigated. The field-uniformity mechanism and the shield effect between micro-protrusions on the rough electrode surface were put forward and demonstrated. Based on the idea that electric field can be shield in a pit, a theoretical model was established to evaluate the maximum field enhancement factor βEmax on the micro-surface. It revealed that 1 ≤ βEmax ≤ 3.96, and βEmax had the maximum decrements of 1.96 and 2.1 both from 3.96 after the mirror polishing and the chemical polishing, respectively. When the surface roughness decreased to the scale from nm to μm, the effort on βEmax reduction through surface polishing was not effective to enhance the vacuum gap breakdown strength any more.