Streamer propagation over a liquid/solid interface

A needle immersed in transformer oil is located just above a sheet of glass of which the opposite surface is conducting. By applying high-voltage (HV) steps, streamers which propagate radially with numerous branches are generated. The characteristics of these discharges (mean propagation velocity, final extension, and electric current and charge) are determined, and the measured charge is compared with the predictions of two simple models. A technique for guiding the discharges gives single quasi-rectilinear streamers, which allows a more accurate investigation. The mean electric current and the final charge indicate that the streamer channels are, to a first approximation, at the potential of the needle. The simple picture of a finite potential gradient along the channels is discussed with reference to the intermittent character of the discharge phenomena