On the nature of prebreakdown emission currents in vacuum interrupters

Characteristics of prebreakdown emission currents were studied for electrodes of CuCr before and after DC breakdown. The characteristics were analyzed by using the Fowler-Nordheim equation for field emission. Measurements were carried out with fresh electrodes and after various conditioning procedures. It was found that the value of the microscopic breakdown field strength E/sub b/ (calculated from the measured field amplification factor beta ) is reasonably constant for all surface conditions, with a value of (8.1+or-1.4)*10/sup 9/ V/m. Therefore changes of the macroscopic breakdown voltage are obviously caused by different values of the field amplification factor. It was found that for all surface conditions investigated there exist well-defined correlations between the parameters beta and S of the Fowler-Nordheim equation. The existence of this correlation and the constancy of the microscopic breakdown strength is regarded as an argument for the equality of the emitting points.<
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