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Ash Small

Mon Mar 04 2013, 06:52PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I've found Bill Parker's original (and apparently only) patent relating to plasma globes. Three of the mixtures he patented use Helium, one with a PP of 10%@480 Torr.

I also found this on the TCML

Interestingly, a member of this forum, Scott Fusare, used to work for Bill Parker.

Carl A. Willis

Tue Mar 05 2013, 01:08AM

Registered Member #9640 Joined: Wed Jan 16 2013, 07:53AM
Location: Albuquerque, New Mexico
Posts: 26

I'm a long-time skeptic of the value of disclosures made by commercial plasma artists about their fills. I don't begrudge these folks their livelihoods or dispute the beauty of what they make, but a lot of what shows up in patents, interviews and the rumor mill must be interpreted with a critical eye for obvious reasons. I mean, just look at some of what's in Parker's patent: fills containing fluorine (which from a practical standpoint, reacts with glass and can't be expected to stick around) and the mention of "radioactive gases", perhaps just to cover his bases. I am a skeptic.

Bill Parker's and Mundy Hepburn's patents mention the use of helium. I take them at their word that they use it. But contrast this with what is said in my Marton "Vacuum Physics and Technology" book:

[...] for a mixture of 0.5% helium in nitrogen stored in glass, the mixture will be greatly depleted of helium within a day at room temperature due to helium take-up within the glass.

A calculation based on Marton's tabulated permeation constants indicates that helium will be transported entirely through a small (1 liter) plasma globe made from Pyrex at a rate of about 10% per year for modest fills of a couple dozen torr and room-temp conditions. That's helium that makes it all the way through the glass, not just captured in the near-inner-surface. The takeaway lesson: For low-pressure fills in large surface area globes, your helium might be effectively sequestered in the glass within a day, while if your fill is higher-pressure He in a small globe, the best you could do would be ~10% loss per year, limited by bulk diffusion. My point here is that I am a skeptic of helium's essential purpose in these mixes. Maybe HeNe lasers use a special glass. Maybe they are filled to a high enough partial pressure of He that the rapid loss is tolerable over the life of the tube. I don't know.

Cheap mass-produced plasma globes contain binary neon and xenon mixes, according to scientific measurements (optical emission spectroscopy and mass spec) made on their contents. The partial pressure of neon is close to atmospheric pressure, and xenon is present in much smaller quantities. See for example Campanell M., Phys. Plasmas 17, 053507 (2010). I think this mix is popular because it is reasonably pretty, simple, strikes easily, and most importantly, is very tolerant of imprecision in the fill.

-Carl

Ash Small

Tue Mar 05 2013, 01:34AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Thankyou for your reply, Carl. I genuinly appreciate it.

While I agree with some of the points you make regarding patents, etc., I'd suggest that, at lower pressures, Helium does not leak out as fast as some might suspect.

The only way to test this is through experiment, unless someone with relevant experience is forthcoming with comments.

I'm in the process of setting up a new workshop at the moment, so it may be a while before I'm able to verify this either way.

Shrad

Tue Mar 05 2013, 07:43AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

helium leak is propotrional to glass temperature, for what it's worth

so it will depend on the energy you feed the globe

Scott Fusare

Tue Mar 05 2013, 09:41AM

Registered Member #531 Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 125

Carl A. Willis wrote ...

Bill Parker's and Mundy Hepburn's patents mention the use of helium.

-Carl

I spent a few months consulting for Parker's company (on plasma etch, not art). The NDA is singed was absurd to say the least so I won't comment on what I learned of his fills. I can however say that he was engaged in legal battle with at least one unhappy customer that had been waiting years for his expensive art piece to be re-filled. I gathered that the need for re-fill was not uncommon. You can draw your own conclusions...

I can also comment (yes this is hearsay) that a mutual friend that worked with Parker when he was artist in residence at MIT early in the plasma art days has mentioned that he buffered the mix with He at that time. (mid-late 70s)

As for his patents, I would think Carl spot in in his assessment. Bill P. is truly paranoid about his "secrets" being stolen by others. He even went so far as to redact the labels on custom mix tanks from Spectra Gas. This in his own facility! Of course, the mix could still be read :)

Scott

zrg

Sun Mar 10 2013, 01:08AM

Registered Member #4762 Joined: Sun May 06 2012, 05:59PM
Location: Russia
Posts: 93

I must admit I was totally wrong about the air influence. Thanks guys, you made me dive into this plasma art again, throwing away boring DRSSTCs and other Tesla stuff.

Perhaps I've never had a truly clean system until now. Anyway, the grass green color in xenon-air mixes is now clearly visible. And which is most important, absolutely no any organic components which mean this perfect green color will remain as long as the glass is not cracked.

That 10L sealed xenon-air flask is the most awesome plasmaball I ever created. Will need to order some more of these flasks.

Carl A. Willis

Mon Mar 18 2013, 03:35AM

Registered Member #9640 Joined: Wed Jan 16 2013, 07:53AM
Location: Albuquerque, New Mexico
Posts: 26

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I have more information to share about the green color. Nitrogen is necessary, but NOT sufficient after all! Oxygen in very small amounts (<1/10 the partial pressure of nitrogen for best results) is also needed to get this color. If a very clean flask is taken at 400 deg. C and pumped, cooled while pumping, then backfilled with ONLY N2 and Xe, a grayish color with only a faint hint of green is obtained. Nitrogen adds its own pinkish coloration and fuzziness to the filamentary structure as its partial pressure rises above about 1 torr, but the green is weak unless a tiny amount of oxygen is admitted. A tube that is not baked at all often requires no oxygen addition for good color, presumably obtaining this impurity from existing contaminants on the walls or in the residual gases. In any case, too much oxygen shifts the color toward a bluish-green and destroys the intensity of the color. Pure oxygen contributes its own yellowish afterglow to xenon's filamentary arc, but the green color requires nitrogen AND apparently a trace of oxygen or possibly another impurity carried in it to turn out well.

So what is this green emission? I don't have a spectrometer, so until I do, all I can offer is some literature references that mention green colors from xenon plasmas with nitrogen and oxygen, and invite speculation about which mechanism is at work here.

Cicconi and Piano flowed Xe at 10-40 torr through an electrodeless RF discharge tube containing residual atmospheric gases in the 1E-4 torr range, obtaining a green color. They attributed the color to a particular excited state of the dimer XeO.

Passow and Brake (Plasma Chemistry and Plasma Processing 9(4), 497-511 (1989) also discuss the emissions from xenon discharges that are attributable to XeO*, presenting energy diagrams, lots of empirical data from different pressures, and a thorough discussion.

Herman and Herman, Nature 191, 346-347 (1961) describe a new RF discharge afterglow emitting green light, in which both Xe and N are necessary. They propose that the emission is either an XeN excimer or one of the unstable states of molecular nitrogen known to be excited in afterglows. This is a very interesting read.

Mannella's monograph on "active nitrogen", Chem. Rev. 63 (1), 1â€“20 (1963) is a very thorough discussion about all kinds of phenomena related to the nitrogen afterglow, including green afterglows from mixtures of Xe and N.

The mystery continues. If anyone has a small, computer-operable spectrometer, or is wise in such things and has a recommendation...lemme have it!

-Carl

Sigurthr

Mon Mar 18 2013, 04:14PM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

I'll have to see if I can get in touch with some old laser hobby buddies over at LPF. Several of them have usb spectrometers. They wouldn't be willing to part with them but they could point you in the right direction for one I'm sure.

Btw; re: my earlier query / search for a white diffuse glow in an electrodeless tube. A physicist acquaintance of mine suggested looking in to Xe + O mixes. He said that he once saw an electrode discharge tube with something like 85% O2 and 15% Xe at low pressure which gave a very pure white glow at sufficient current, but that the O2 quickly destroyed the electrodes. He suggested trying a similar mix in an electrodeless tube.

Any of you guys up for testing it?

zrg

Tue Mar 19 2013, 08:02PM

Registered Member #4762 Joined: Sun May 06 2012, 05:59PM
Location: Russia
Posts: 93

Discovered a funny effect while playing with xenon and ~30 MHz generator.
The inductively coupled plasma acts similar to a ball lightning.

klugesmith

Sat Mar 30 2013, 12:56PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Speaking of electrodeless plasma discharge tubes ---
has anyone here tried making Violet Ray wands, in traditional or novel shapes?

Or perhaps refilling commodity V.R. wands with better colored gases?
I just discovered commercial sets available in neon red!

and unexpected accessories from the Violet Ray's heyday (early 20th century):

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