The evolution of pulsed discharges over PTFE in the presence of various cover gases

The spatial structure and temporal evolution of surface discharges have been studied. The substrate was a sheet of PTFE that was 0.5 mm thick and the cover gas was argon or nitrogen. The surface discharges were capacitively coupled to an earth plane that was located on the underside of the substrate. High-speed digital photographs were taken of the surface discharge development and these have shown that the structure was dependent upon the gas type. Uniform discharges tended to form in argon whereas filamentary discharges were prominent in nitrogen. It was also found that the amount of energy stored in the external circuit capacitance influences the nature of the surface discharge by determining both its width and uniformity.