The effect of mechanical contact on breakdown characteristics in vacuum

Using copper-chromium electrodes, an experiment was conducted to clarify the reduction of insulation strength by mechanical contact in vacuum. The experiment consisted of prebreakdown current measurements and SEM (secondary electron microanalyzer) observation of the electrode surface. Experimental results revealed that the field intensification factor obtained from the prebreakdown current was increased by mechanical contact. SEM observation showed that mechanical contact caused microprotrusions to be generated. This phenomenon suggests that a reduction of insulation strength by mechanical contact is caused by field emission from a roughened surface. If mechanical contact is made, dielectric breakdown occurs when the field strength of microprotrusions on the cathode surface reaches a critical value (1.0 to 1.7×10⁸ V/cm)