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Re: [TCML] Would a Tesla coil work in a vaccum?



Hi Greg,
I can chime in here, the color of discharge is greatly effected by the humidity and particulate content of the air, as well as current density of the arc. Allow me to explain the basic mechanics by which sparks make light, the atoms in the air are floating around with all their electrons in their lowest orbital states, when they are energized (by heat like with fire, or in this case raw electricity) the outer electrons shift orbitals to a higher energy level. When they lose that energy (which they inevitably do) the electrons come back down to where they belong and emit a photon of an exact frequency. Different elements emit different frequencies based on energy input (hotter fire, or more current.) Dirt in the air will burn encouraging a more orange color (maybe) and humidity will favor a more blue color (probably.) Another very interesting thing to note, is that fire is orange because of the ionized carbon/wood/smoke in it, and if you use high enough current you can ionize and vaporize the metal electrodes (aluminum makes a brilliant aqua blue, and lead solder is dark blue (use ventilation...)) Your grounded arcs have higher current and so the electrons shift higher and the result is brighter. Your Jacob's ladder arc is billowy and thick because high current and high "on time" (most of the time the tesla coil arc is off, so the current stays in a thin bright streamer and does not have time to spread, if you take an instantaneous picture of a Jacob's arc ladder forming it is also a narrow bright channel, which almost immediately spreads out to allow greater current.) This is also why some tube and solid state coil sparks are thick and bushy, they have a higher duty cycle than a disruptive TC so the arc has time to grow. As for photographs the difference is because the camera isn't sensitive to all the frequencies the human eye is, and since sparks emit definite frequencies instead of a broad band like sunlight, if the camera isn't sensitive to one it looks wrong. I explain this a bit here on my Plasma globe webpage.
http://bogard.110mb.com/Plasmaglobe.htm

Scott Bogard.

G Hunter wrote:

Hi Bill,

Interesting stuff, which raised still more questions in my slowly calcifying, middle-aged brain.  For example, why are Tesla coil sparks the color they are?  Presumably, ionized air contributes the color.  But if that's all there is to it, why aren't all TC sparks the same color?  Even in my own coils, I've observed discharges of violet, violet-white, purple, blue, and various shades of blue-white.  Likewise, Jacob's ladder sparks are orange and flaming, while TC spark gap sparks are intense blue-white.  How can an ionized 80/20 Nitrogen/Oxygen mix at 1 atm glow at so many different colors?  Is it just a matter of temperature?  What about impurities?  I suppose the JL uprights might contribute metal ions and metal vapor, which could explain the dramatic color difference.

Oddly, what the camera sees and what I see don't always agree.  Sparks that look blue-white to me may render as violet in photographs, or vice-versa.  This is troubling as my cameras and I tend to agree very well on the colors of other subjects.  Why the disagreement on the color of TC discharges?

Regarding the ultra-high vacuum situation:  what about a thermionic electron tube?  Is a visible discharge inside such a tube possible?  I'm assuming the answer is "no", but what about a very high current through a hard vacuum?  Still invisible?  I guess I'm just fishing around for an answer to the ultimate question:  What color is an electron???

Greg


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