Plasma and electrode interactions in short gap discharges in air I. Plasma effects†

Breakdown in a matched 125 Ω coaxial cable system was studied using the following techniques : namely, (a) current/voltage measurements using fast oscilloscopes ; (b) spectroscopic investigations of the light emissions from the various discharges ; (c) scanning electron microscope studies of the damage on the electrode surfaces, and (d) open shutter photography. The observations reported indicate that short duration coaxial cable discharges in air at atmospheric pressure involve a transition through a glow discharge. The duration of the glow appears to be dependent on the condition of tins electrodes surfaces. The glow appears to contract before its transition into an arc regime. This transition time has been measured and is suggested to be the formation time of the cathode spot. The electrode aspects of this study are presented in the companion paper; II. Electrode effects.