Positive and negative pulsed corona in argon

Photographs are obtained of corona discharges in argon at atmospheric pressure using a high resolution, intensified CCD camera. Positive and negative polarity is applied at the curved electrode in a point-plane gap and a plane-plane gap with a protruding point. Branching is observed in the positive point-plane gap but it is much less pronounced than in air probably due to the much lower energy input. The positive point-protrusion case does not show branching and it very rapidly develops into a spark breakdown. The negative corona in argon requires roughly a two times higher average applied field to develop a discharge. Its appearance is diffuse in the point-plane as well as in the planeprotrusion case. Since the inception voltage and the breakdown voltage in argon are quite close to each other it is not possible using the present set-up to obtain experimental results at the very high field condition where a new theory predicts streamer formation and branching in negative corona.