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 were obtained from which the path could be determined in three dimensions by subsequent computer processing and analysis. Some 80 images were analyzed for each of five angular positions of the point electrode's axis, the gap remaining constant. The fractal dimension of each path was determined and found to increase slightly with the inclination of the pointed electrode. Each spark appeared to have propagated semi-randomly in a direction which included 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 the previous step. These, and other analysis, suggest that the development of 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 propagating leader.