Streamer discharges are the primary mode of electric breakdown of air in lightning and high voltage technology. Streamer channels branch many times, which determines the developing tree-like discharge structure. Understanding these branched structures is for example important to describe streamer coronas in lightning research. We simulate branching of positive streamers in air using a 3D fluid model where photoionization is included as a discrete and stochastic process. The probability and morphology of branching are in good agreement with dedicated experiments. This demonstrates that photoionization indeed provides the noise that triggers branching, and we show that branching is remarkably sensitive to the amount of photoionization. Our comparison is therefore one of the first sensitive tests for Zheleznyak's photoionization model, confirming its validity.
Streamer discharges often exhibit branching, which can greatly affect their behaviour and will lead to so-called streamer trees. In this work we present a methodology for investigating the structure of a streamer discharge tree by means of advanced imaging techniques.
Stereoscopic and stroboscopic techniques augment the images with depth perception and temporal information relevant to study the inherently stochastic three-dimensional and transient streamers.
A semi-automated post processing algorithm is developed to make a reconstruction of the streamer discharge tree formation.
This results in a tree of streamer segments, separated by branching events, where velocities, diameters and trajectories are used to characterize the morphology.
The workings of the algorithm is detailed using an exemplar measurement series of positive streamers in synthetic air at 233 mbar.
Streamer discharges are the primary mode of electric breakdown of air in lightning and high voltage technology. Streamer channels branch many times, which determines the developing tree-like discharge structure. We simulate branching of positive streamers in air using a 3D fluid model with stochastic photoionization. The distributions of branching angles and branching locations agree quantitatively with dedicated experiments. The simulations are sensitive to the photoionization coefficients, and they confirm the validity of the classical photoionization model.
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