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Re: Leader Strike Photo



Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Bert,

I think our "newfound" high-speed streamer photo advantage is now in day 19 (much spent in ordering special parts!)... Here, things or in total chaos and confusion %;-)) The LM3914 thing fell flat, and now LM319 things are on the mind. Long since forgot which polarity is which anyway... @:D

I think both Peter and I stare at "hundreds" (approaching thousands) of photos and we "select" which ones to tell about...

My coil is a solid state DC disruptive coil with very reproducible polarity and power ringups... Almost "cheating"... The whole polarity could be easily reversed by switching primary leads... But we have "too many" variables"... To many things "to do"...

We can provide the data, but there is so much!! We can't figure it all out... So tell us what "you want"? We have more knobs than we have fingers now... Maybe more folks will hook up mirrors to get a more divergent view on all this!!

"Great pictures" are running 1/50 now... I need to order more NiMH batteries to keep up ;o))

Higher RPM on the mirrors seem to really help now to streeeaaatch things out... We have more answerers than we have questions...

Cheers,

        Terry


Antonio, Terry, and all,

It has been amply demonstrated that leaders and streamers are initiated, and propagate, at lower E-fields within a diverging positive E-field than within a diverging negative E-field. And, the underlying propagation mechanisms are significantly different for positive leaders versus negative leaders. Under sufficient fields, a positive leader will grow more or less continuously, while a negative leader proceeds in discrete jumps, forming bright, isolated, leader-like "space stems" ahead of the negative leader. Each space stem has streamers coming off BOTH ends - positive streamers towards the advancing negative leader and negative streamers on the other end. (BTW, this is also observed during stepped leader growth during negative lightning propagation). And, some of Peter's streak photos actually appear to show space stems. For example:
http://tesladownunder.com/HVRotMirrorPolarityNegLeader.jpg

Both Peter and Terry are presently using "rod-rod" electrode configurations which complicate the shape of the initial E-field in the gap. It would be interesting to see if they see different results when using a rod-plane or a rod-wire configuration instead - theory predicts that this should cause significantly more streamer and leader branching in the gap. Of course, once leaders and streamers start growing within the gap, previously injected space charge and topload voltage reversals dramatically complicate things. =<:^O

At higher average E-fields and longer sparks, the propagation "advantage" of a positive source tends to disappear, and negative leaders appear to grow (macroscopically, at least) at fields similar to positive leaders. And, branching occurs with either polarity as the discharge propagates into weaker field areas. Similar branching behavior is readily observed for both positive and negative lightning.

Branching of streamers and, (for long gaps) leaders, appears to be inherent to dielectric breakdown of gaseous, liquid, and even solid dielectrics (electrical treeing and Lichtenberg figures). Branching angles fall between 30 - 40 degrees (i.e., 15 - 20 degrees on either side of the previously unbranched leader direction). And there are lots of interesting theories (and various simulations) that hint as to why this is the case.

Bert
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