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Vertical distance. Branching angle. Stereophotographs of point-plane streamers in air S. Nijdam 1 , J. Moerman 1 , T. Briels 1 , E. van Veldhuizen 1 , U. Ebert 2 1 Technische Universiteit Eindhoven, Dept. of Applied Physics

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  1. Vertical distance Branching angle Stereophotographs of point-plane streamers in air S. Nijdam1, J. Moerman1, T. Briels1, E. van Veldhuizen1, U. Ebert2 1Technische Universiteit Eindhoven, Dept. of Applied Physics Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands 2Centrum voor Wiskunde en Informatica, Amsterdam Introduction • Set-up • Similar set-up as used by Tanja Briels • Positive streamers, 47 kV, 6ns rise-time, 16 cm gap • Measurements in air 200 – 1000 mbar • Problems: • Interpretations often ambiguous • 3D spatial structure not known • Impossible to measure branching angles • Streamer photography usually only provides 2D information • Streamers are a 3D phenomenon • Method • Use 2 prisms and 2 mirrors to get 2 images on 1 CCD • Superimpose the 2 images in different colours to create an anaglyph image • Select same streamer section in both colours • Check line positions in original image • Use pixel size, set-up geometry and observation angles to calculate 3D position of streamer section • Repeat this method for all suitable streamer sections Example pressure: 200 mbar Original image Front view Left view Front view Left view Anaglyph image with streamer section selected Selected streamer shown in 3D Multiple streamers shown in 3D Results: Branching angle distributions at different pressures and fixed V Results: Branching angle vs. distance to tip • Branching angle is distributed statistically • Branching angle does not depend on pressure • Large spread in branching angle • Branching angle does not depend on distance to tip • Conclusions • Stereo photography method works excellent, although not for all streamer situations • Image processing is somewhat labour intensive but not difficult • Automatic processing probably too difficult to pursue • Branching angle does not depend on pressure or distance to tip, hence on reduced electric field • Branching angle is distributed statistically • Future work • We are working on: • Stereo photography with a 2-point-plate configuration • Comparison air vs. nitrogen and other mixtures • Measuring speeds and other distributions from these 3D data sets

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