General Physics Physics Seminar 14 November 2002


Spontaneous branching of discharge streamers

Ute Ebert

National Research Institute for Mathematics and Computer Science (CWI),
Amsterdam, The Netherlands


If a strong electric field is suddenly imposed on non-ionized media, electric break-down initially occurs in the form of streamers: fast growing, space charge dominated, weakly ionized structures. They play a role in normal lightening, in the recently observed upwards lightening (sprite discharges) as well as in many engineering problems in gases, liquids and solids.

In experiments, streamers are seen to branch spontaneously, and accurate measurements with nanosecond resolution are now becoming available. On the theoretical side, phenomenological models for streamer branching with stochastic elements have been suggested, but without a proper link to the underlying discharge models. However, we recently have found streamer branching in a simple fully deterministic continuum model for the particle densities. The branching mechanism is a Laplacian instability similar to the one causing tip splitting in viscous fingering. We elucidate this mechanism both with simulations and with analytical conformal mapping techniques and discuss the conditions of the instability.

For publications see http://www.cwi.nl/~ebert/branching.html