An Experimental Study of the Breakthrough‐Phase and Return‐Stroke Processes in Long Sparks

The dynamics of the brightness of a long‐spark channel during the breakthrough and the return‐stroke phases of discharge development were experimentally studied using streak‐camera images synchronized with current recordings at the high‐voltage electrode. The velocities of primary positive leader developing from the high‐voltage electrode and connecting negative leader extending from the grounded electrode during the breakthrough phase were measured as a function of the discharge current and the distance between leader tips. The velocities of the return‐stroke waves propagating upward and downward along the positive and negative leader channels, respectively, were also measured. The connection region exhibited channel splitting and reduced brightness relative to the channels above and below it.