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Re: green plasma globe

Original poster: David Speck <dave@xxxxxxxxxxxxxxxx>

Guys,
The precise gas mix that gives green streamers is, still, to the best of my knowledge, a closely held secret. I have had a Bill Parker "Star Sculpture" plasma globe that displays green streamers with red feathers on the ends since 1983 and have not been able to definitely determine the fill.
Even Parker's employees don't learn the gas compositions except on a "need to know" basis. Scott Fusare (if he still monitors the list) can tell you about that.
Plasma globes operate without the heating effects that would be necessary to get copper vapor or sodium vapor. Metal plasma lasers have heavy duty heaters to make the metal vapor that is required for their operation, and no such components exist in a plasma sculpture.
Mixing gasses is often unsuccessful, as one gas will have a lower breakdown voltage and essentially hide the effects of any other gas.
I've heard of folks who have tried to duplicate certain gas colors, but found that tiny traces of contaminant gasses completely hid the expected discharge color of the gas that was the primary and desired fill agent.

My best bet is that the globes contain one of the nine (IIRC) isotopes of xenon. If you look at the rare gas suppliers pages on the net, it seems that xenon has three common isotopes which account for about 40%, 30%, and 10% of the naturally occurring gas. The other isotopes together make up the remaining 20%. Xenon is an expensive rare gas, even in the unsorted version, and isotopically purifying it adds considerably to the expense. To make matters worse, the plasma sculptures run at nearly atmospheric pressure, and the volume of a 12" diameter sphere comes out to about 15 liters, according to Google's convertor, so you are talking about a major investment in rare gas even for a small display. Scott told me that one unique Parker sculpture that I really liked required $20,000 worth of a gas isotope to fill a 12" globe. It had very thin, twisty hyperactive lavender streamers the size of grocery string with green feather at the ends. An exquisite piece, but he only built one, for understandable reasons.
Krypton also comes in 5 or 6 isotopes, so one of them might be a possibility as well. I don't think that the halogen gasses would be good candidates, as they would eventually attack the glass walls and be consumed. My green sculpture still works after almost 22 years, though I don't run it all the time.
I've looked for spectral emission charts for the rare gas isotopes without much success. Perhaps some one on the list might point out a place where the spectra could be found. If you found an isotope with strong lines in the green, that might be your candidate for the green globe.
HTH,
Dave

Tesla list wrote:

Original poster: "Mike" <mike.marcum@xxxxxxxxxxxx>

Not sure exactly, probably argon or some other "neon" gas with a touch of copper vapor to give it the green color. Or some mixture of yellow (sodium?) and blue (nitrogen?) gas.

Mike
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Friday, January 21, 2005 6:03 PM
Subject: green plasma globe


Original poster: Vladimiro Mazzilli <mazvla@xxxxxx>

I've seen in a Paris scientific museum a plasma globe with normal clear
glass a very nice dancing discharge of intense green colour and
I've seen it another time in a plasma globe site without explanation.
Anyone know the gas mixture.


Cheers

Vladi.