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PV: Plenarvorträge

PV IV

PV IV: Plenarvortrag

Dienstag, 18. März 2003, 09:45–10:30, FO1

Spontaneous Branching of Discharge Streamers — •Ute Ebert — CWI Amsterdam, NL — Dept. Physics, TU Eindhoven, NL

Streamers are a common and basic phenomenon in electric breakdown. They appear in the initial stages of natural sparking as well as in various gas discharge reactors. Streamers also play a role in the recently observed upwards sparking from a cloud towards the ionosphere. Frequently streamers are seen to branch.

It is generally accepted that the streamer properties are determined by space charge effects. Space charges enhance the field at the rapidly propagating head of the ionized streamer channel and create an active ionization zone that now can be visualized by fast CCD cameras. To date, a detailed understanding of the ionization reaction and space charge dynamics in the streamer head is missing.

Working towards this goal, we have found that already the minimal continuum model for anode directed streamers can exhibit branching. Taking the field in our numerical solutions twice as high as previous authors, we enter a new parameter regime where the streamer approaches the limit of “ideal conductivity” [Lozansky, Firsov]. The motion of the ionization front around the head can be analyzed by evaluating the Firsov limit with methods borrowed from a hydrodynamic moving boundary problem, namely viscous fingering. Our analytical solutions show how streamers indeed do branch due to the same Laplacian instability.