Point-to-Plane Corona Onsets

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Abstract
The effect of point material and point radius of curvature on positive and negative intermittent corona onset potentials has been studied with a point-to-plane gap in air at atmospheric pressure. The negative Trichel pulse onset strangely is independent of point material but does depend on point history and radius. This surprising result is shown to come from the circumstance that the Trichel pulse onset depends on current densities needed to condition the point surface and yield a higher value of the second Townsend coefficient to give the increased currents. Trichel pulse onset thus does not mark the onset of a self-sustaining discharge. The self-sustaining discharge initiates at lower potentials and leads to currents of a low order until the cathode spot cleans up.