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Registered Member #29
Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500
You may be right... I am no expert in the theory of discharges. However, if I am not mistaken, the Crooke's dark space is space-charge driven effect in low-density plasmas (in vacuum environments, etc.) Since we are talking about a developed discharge (dense plasma "tube") with considerable current density, I would be inclined to look to current-driven effects first...
Registered Member #118
Joined: Fri Feb 10 2006, 05:35AM
Location: Woodridge, Illinois, USA
Posts: 72
Peter,
Very interesting pictures! You may have captured the gaps between isolated "space leaders" and a nearby negative leader. During the propagation of a negative leader, an isolated, bright section (called a "space stem") can be formed within the gap. This may then grow to become an extended "space leader" as the isolated discharge propagates in BOTH directions, being fed by a negative corona (actually a multitude of streamers) at one end, and positive corona at the other. It seems to be a fundamental process during negative long spark propagation
The unique combination of a declining TC terminal voltage and camera setup may be allowing them to be seen. Normally these gaps will be rapidly filled as the discharges propagate and merge with a nearby negative streamer. However, if the topload voltage declines after their initial formation, further propagation may be arrested. I'm not sure if this explains the cases where the gap is entirely bridged, however. See Gallimberti, "Fundamental Processes in Long Air Gap Discharges", by I. Gallimberti, G. Bacchiega, Anne Bondiou-Clergerie and Philippe Lalande, Comptes Rendus Physique, Volume 3, Issue 10, December 2002, Pages 1335-1359. Page 1339 has a picture of ioslated space leader occuring during negative leader propagation - see:
Registered Member #10
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
I am glad that someone who knows "stuff" has relieved me of my off the cuff theories.
Interesting indeed.
Just some more detail of interest with the TC/Rotating mirror. This shot shows the spark travelling down the picture. The features are the initial bright spark (uppermost) with a gap then the ionisation fades out over 22 pixels (2.2uS). Interestingly there is a green flash lasting 2.8us at the electrode end, presumably of ionised copper. This is not strong with the initial spark but builds up as the ionisation is fading.
This is the type of time varying detail that I want to capture. If need be the speeds could be increased further but already measuring in 100ns units is pretty cool for home made stuff. May be 10ns timebase might show more stuff
Edit: This rotating mirror stuff leads into a whole fascinasting new topic which I have continued as a new topic in the Tesla coil forum: high speed Tesla photography.
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End-on spark view - broken sparks
