An analysis of spark paths in air using 3-dimensional image processing

A video camera has been used to record the path of spark breakdowns across a positive point/plane air gap. By using a prism as a mirror, two images we re obtained from which the path could be determined in three dimensions by subsequent computer processing and analysis. Some 80 images were analyzed f or each of five angular positions of the point electrode's axis, the gap re maining constant. The fractal dimension of each path was determined and fou nd to increase slightly with the inclination of the pointed electrode. Each spark appeared to have propagated semi-randomly in a direction which inclu ded a 'memory' factor, ie. it tended to follow the previous direction while moving monotonically towards the opposite electrode. This was confirmed by considering a projection of the spark path onto the plane electrode which was found to form a semi-random walk in which each step was influenced by t he previous step. These, and other analysis, suggest that the development o f spark paths in air by successive steps is in a direction suggested by an angular probability distribution related to the field at the tip of the pro pagating leader.