Statistical Property of Breakdown Between Metal Electrodes in Vacuum

The statistical property of breakdown voltage of vacuum gaps ( 2 x 10-6 Torr) was studied experimentally using parallel plane copper electrodes in the gap length of 3 mm to 20 mm. The results are summarized by expressing the cumulative probability of breakdown as a function of applied voltage and the gap length. It was found that the 50% breakdown voltage for the electrode with uniform field is expressed by the relation V - i. The 50% breakdown voltage for the electrode with non-uniform field is lower than the voltage derived from the relation V - ´i. It is shown that the breakdown property in the nonuniform field can be explained as well as in the uniform field by introducing the concept of effective area of the electrode surface.