From long laboratory spark to lightning

We investigate the growth of meter-length discharges with a 2 MV Marx generator. A high-voltage divider and separate current probes mounted on two cone shaped electrodes provide the electrical parameters. Two LaBr3 detectors recorded the emerging X-rays. Two 0.2 ns fast ICCD cameras provide optical images of the growing discharge; when triggered sequentially, the cameras also determine the propagation direction of the discharge fronts. At negative high-voltage, we observed bipolar phenomena at some distance from the negative leader tip. Negative streamers originate from the leader and leave ionized channels behind. But also positive streamer heads show up and these move towards the leader. X-ray detection coincides with the collision of positive streamers and negative leader. Later on, space leaders are observed to form. Our laboratory observations look similar to the step-wise propagation of natural lightning.