Figure 3

Time evolution of the ionization front in (a)–(d) air-filled, (e)–(h) CO\(_{2}\)-filled point-point gap. Panels have been labelled with the moment in time the image was recorded. Showing dU/dt = 50 kV/ns, the distinction between anode and cathode is indicated by the ‘+’ and ‘–’ symbols printed on the needle electrodes.