Electric and Spectroscopic Analysis of Surface Corona Discharges in Ambient Air and Comparison With Volume Corona Discharges

This paper is firstly devoted to experimental electrical analysis of a dc surface corona discharge in ambient air at atmospheric pressure and room temperature. The surface corona discharge is established between a positive pin and a grounded plate electrode, set on the same side of an insulating plate made either in polymethyl methacrylate (PMMA) or in polytetrafluoroethylen (PTFE). The interelectrode distance, the tip radius of the pin, the applied voltage to the pin, and the nature of the dielectric have been parameterized, and discharge currents are analyzed. It is shown for instance that the surface corona discharge can be ignited over a PMMA dielectric for an applied voltage 20% lower than the PTFE case. This is coherent with calculations of electric fields which are, in the pin region, 25% higher over PMMA than over PTFE. Electrical characteristics of dc surface corona discharge are then compared with those obtained in the case of volume corona discharges generated in the same ambient atmospheric air by using the same positive pin in front of a copper cathode plane. It is observed for the same conditions (applied voltage, gap distance, and tip radius) that the surface corona discharge develops with a higher discharge current even if the UV-visible spectra of both surface and corona discharges remain quasi-similar. This better electric efficiency of surface corona discharge in comparison to volume corona is confirmed from calculations of electric fields and corresponding production rates of certain active species near the pin using multiterm Boltzmann equation solution and literature electron-molecule collision cross sections for electrons impacts with ambient air.