Method

1
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
Left view
Front view
Left view
Front 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

• 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

• 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