Recent understanding of streamer discharges by combining experiments and numerical modelling

Streamer discharges are self-organizing discharges which occur when a fast high voltage pulse is applied, leading to a local, but not global electric field above the breakdown field. These ionization waves can then penetrate areas below the breakdown field. Streamers occur as a precursor to sparks and lightning, but also as separate discharges. In recent years, both simulations and diagnostics of streamer have made great steps, so great that they allow us to compare simulation results now directly to experiments and see that their results agree very well. In this contribution, the basics of a streamer discharge will be explained.

Besides this, some examples of recent diagnostics will be discussed, which help us to bridge the gap between experiment and simulation. We will show how we can use a combination of stereoscopic and stroboscopic imaging to determine the path of a propagating and branching streamer discharge. We have developed a semi-automatic routine to reconstruct this path from the images, giving us a complete picture in 3D of streamer velocity, diameter and branching properties. This data will be compared to numerical streamer simulation results obtained using the 3D Afivo streamer model.

Finally, we will show how we can use the E-FISH diagnostic to fully probe the electric field distribution of a single propagating streamer in air. By means of a combination of advanced processing, including an Abel-like inversion process with a detailed scan, we can work around issues like phase-vector mismatch, Gouy phase and background interference to make a combined image of the radial and axial components of the electric field.