Space-charge fields of positive point¿plane discharges in air and nitrogen

The spark-breakdown mechanism of positive point-plane gaps in air and nitrogen has been studied using a probe technique to record the electric-field variations at the plane electrode caused by space charges in the gap. The technique involves oscillographic recording of the integrated displacement current through a small probe of 1 cm diameter mounted flush with the surface of the earthed plane. The results described refer to a 15 cm gap subjected to impulse voltages of 1 ¿s wavefront and 50 ¿s wavetail. The point electrode consists of a cylindrical rod with a square-cut end of 1.1 cm diameter. Further information about the physical processes affecting the growth of the discharge has been gained by observing the effects on the field of changing the oxygen concentration in nitrogen.