Dave and David,
The main difference here between regular Tesla coil corona discharges and so called "phantom streams" is that the later have very distinct fractal patterns in the air and
aren't mere diffusion. The "Phantoms" as per Tesla's lectures were mentioned as perpendicular lines darting out a foot or more in all directions - this is what happens at moderate power levels. If you reduce the power to less than 50W and have certain other conditions correct (ie, the spark gap must fire slowly, and be adjusted in really small increments, the transformer/cap must fall within a range to allow the gap to fire intermittently, the topload must not be too big nor too small etc etc...)
The positive streams - which are the most typical and easiest to acquire - have a really cool fractal pattern like this:
http://www.electrotherapymuseum.com/2012/Kinraide7MP/content/_8035002824_large.html
With a 200T pancake coil and 8-10mA neon (3-5kV) the discharge is faint but so intensely propagated that a 2" copper ball with produce the streams a foot or more
radially in all directions - literally a 2 foot sphere of activity.
If the gap is opened very slowly and precisely the sound of the discharge will change and the branches will grow to nearly a 1/2" in diameter yet retain the patterns - as in this photo:
http://www.electrotherapymuseum.com/2012/Kinraide7MP/content/_7306920280_large.html
At points if the gap is opened more, a negative oscillation or oscillations will appear interposed as this:
http://www.electrotherapymuseum.com/2012/Kinraide7MP/content/_3652576312_large.html
Normally the negative is smaller and slightly fish-tail in appearance:
(A good example)
http://www.electrotherapymuseum.com/2012/Kinraide7MP/content/_0260820729_large.html
A pure negative discharge will normally only appear when dielectrics are interposed and induced discharges occur:
http://www.electrotherapymuseum.com/2012/Kinraide7MP/content/_2390004612_large.html
Occasionally the negative plumes have a curious shape like this:
http://www.electrotherapymuseum.com/2012/Kinraide7MP/content/_6344063482_large.html
It took a long while to decipher the why and how. I need someone with fancy gear. These baby neons, or regular neons when operated with a lot of resistance or a variac to limit the total power level to much less than 30mA (5-15 seem to work best) actually pulse the Pancake Coil with a messy DC - like an induction coil with a mechanical interrupter. For whatever reason certain settings of the gap produce just the right pulse to allow the very distinct formations in the air surrounding the terminal. Simply rectifying the output of the NST or trying to force the spark gap to rectify it (point - plate gaps, etc) can show a little of the effect but the strongest (and drastically surprising - like the 1/2" thick branches) happen without any real departures from the norm. The best as can describe it, the same way you can get mains resonance with any xfmr at specific power levels and cap sizes, you can also get a strange rectification of sorts when you combine a xfmr, cap, and spark gap. Even If you leave out the primary and replace it with a polarity indicating Geissler tube you can see it clearly, and with this later tube you can watch as one pole lights (showing the negative pole) and how adjusting the gap the polarity may suddenly reverse, or at certain intervals the discharge is purely oscillatory and on adjusting the gap one pole will be predominantly positive or negative...its really strange and a lot of fun.
With cylindrical coils as Tesla used the fractals tend to be washed a lot into the straight lines, with pancake coils as Kinraide used it is much easier to produce the fractals and very distinctly produce them.
Even on the video Frank Jones' old android phone (which is the only camera I've had luck to show these, including a $6000 borrowed UV camera with quartz lenses) you can only see about half of what the naked eye could see.
One day we all must just meet for once and I can show you all in person. Its a lot of fun. I collected hundreds and hundreds of antique Tesla Coils, and while they were all a little different and interesting these Kinraide experiments were personally the most mind-blowing for me. I was fortunate to acquire the old glass negatives to strike my curiosity...to see them in person, 1890s, hold in your hand one of the original coils that made them, and then to see the actual discharges and hear the strange sounds of the spark formations, the sounds from the spark gap even, its all a really different side of Tesla Coiling, and different in a good way because at some point we all think we've seen it all and nothing can be better than witnessing the unexpected "live".
This future museum project, well, this style of coil will be a special feature just for the coiling crowd. I won't have the biggest Tesla Coil but what I will have are coils that inspire people to try something new...
one of the few TCML members that came to the house was David Sharpe... a great guy. I remember the look on his face a few times when he saw things he wasn't expecting. Like the 100T secondary coil from the Mcintosh Hogan throwing a hot purple arc about 10" long. We had a great laugh over that...
The fun things about all of this stuff, even something as crude and simple as a spark gap Tesla Coil can take you off guard. When you operate a Tesla Coil with a 100kV X-Ray transformer, or a 16-plate Static Machine, or a 900V transformer and 1/2 mfd cap the outputs are as different as night and day!!
Jeff
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