Electrical breakdown mechanisms in vacuum diodes

The aim of this paper is to determine a statistical model which provides a satisfactory description of the “vacuum breakdown voltage” random variable and its relation to the vacuum breakdown mechanism. For that purpose, theoretical and experimental investigations of pulse and dc breakdown voltage statistical properties in two-electrode vacuum-insulated diodes were conducted.During the experiment vacuum pressures were 10−9, 10−6, 10−4, 10−3 bar and inter-electrode gaps were 0.1, 0.3 and 0.5 mm. Cylindrical copper electrodes with polished surfaces to a high glam were used. The field in the inter-electrode region was homogeneous with slight inhomogeneity at the edges of the electrode system (edge effects). According to results obtained it should be pointed out that, under conditions of the experiment, at the pressure value of 10−9 bar breakdown mechanism is emission mechanism of cathode type, while at the pressure of 10−6 and 10−4 bar breakdown mechanism is combination of emission mechanism of cathode type and vacuum avalanche mechanism, while at the pressure of 10−3 bar breakdown mechanism is Townsend gas mechanism with occurrence of anomal Paschen effect.