ac (50 Hz) and dc electrical breakdown of vacuum gaps and with variation of air pressure in the range 10-9-10-2 Torr using OFHC copper, nickel, aluminum, and niobium parallel planar electrodes

Abstract

Breakdown potentials of vacuum gaps are measured over a wide range of air pressure using both direct and alternating (50 Hz) applied voltage and employing four different electrode materials. The air pressure is varied in the range 2×10-9-2.5×10-2 Torr for dc and 6×10-7-2.5×10-2 Torr for ac applied voltage. OFHC copper, nickel, aluminum, and niobium are used to fabricate the electrodes. It is found that the peak ac breakdown voltage is usually higher than the dc voltage for a fixed electrode separation and a fixed gas pressure. Under certain conditions considerable improvement in the insulating property of the gap can be obtained in semivacuum. The improvement in the breakdown voltage of the gap is considerable and can reach up to 62% in some cases. The higher breakdwon voltage is attributed to the increased work function of the metal-gas adsorbate system.