Area effect on electric breakdown of copper and stainless steel electrodes in vacuum

The breakdown field strength E_b(= alpha Vb/d) of gaps made with pure copper and stainless steel depends on the effective area S_eff. It can be expressed by the single experimental equation E_b=K₁S_eff^-n, where K₁ is a constant, n is about 0.24, S_eff is the electrode area subjected to more than 90% of maximum field strength, alpha is the shape factor, d is the gap length, and V_b is the breakdown voltage. The field intensification factor beta _l obtained through the measurement of prebreakdown current can be expressed by a single experimental equation beta _l=K₂S_effn, where K₂ is a constant. This means that the area of effect of E_b is represented by the area effect of beta _l and that the vacuum breakdown may be initiated by field emission.