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Steve Conner

Wed Feb 27 2013, 04:08PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

No, I junked it many years ago. It started out with the ordinary mix used in plasma balls, giving blue streamers with orange tips. According to your findings, the most likely explanation for the green colour is that it sprung a slow air leak.

Sigurthr

Wed Feb 27 2013, 08:56PM

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

Hi Carl, your tube work is amazing. Outstanding colors and filament formation. I've been working with two amateur plasma tube makers over the last year or so on various projects/tubes and I'd like to include you in the loop so to speak on a recent project, and also ask if you could verify the phenomena I've found in one of my tubes. We've been trying to get diffuse glows in two colors; white (Xe and/or Kr) and a dark blue (think 450nm).

My high pressure Neon (250Torr) tube exhibits a bright white central filament with feathery red tentrils when sufficient voltage is applied. I have observed not a continuum (as a massive mix of gas or contamination with Ar would suggest) but rather many distinct spectral lines across the spectrum from UV up through infrared that do not match the normal Ne spectrum. The Ne lines are in there as well, but it looks more like a spectral mix of Ne + Xe + He + H. The strange thing is the glassworker I had make this tube ONLY had access to Ne, N, Ar, and He. He only had 30Kv to play around with and was not able to bring out the white filament that even a small SSTC can produce from this tube. Any verification of 250Torr Ne white filament formation would be greatly appreciated. Here is a screencap of the tube exhibiting this phenomena:

For the white we got very close by precisely controlling the RF field exposure of a normally filamentary discharge Xe tube by adjusting orientation and distance of the tube within a CW SSTC's e-field. Results were not always 100% reproducable and a bothersome green tint often resulted. It seems that the effect mostly appeared at the cusp of full dielectric breakdown of the fill gas. Unfortunately the pressures were not able to be carefully adjusted so no low pressure work was tested. Do you think you could do some tests and see if you can achieve a full tube diffuse white glow?

For blue, again it was mostly by controlled exposure to a TC's RF field with a rough mixture of Xe + I. Any leads or tips you might have would be greatly appreciated!

Carl A. Willis

Wed Feb 27 2013, 10:43PM

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

Hi Matt,

Thanks for your compliments. As of today, I have a neon tank (250 liters!), so I can probably investigate the neon @ 250 torr observation soon enough. From previous experience with neon (I "borrowed" a little for mischief while I was at an undergrad research program at Kansas State back in the summer of 2000), I can report that it forms beautiful orange filaments at atmospheric pressure, provided the drive power is high enough. So I'm suspicious that the color you report is indeed some contaminant. But we will see!

For a diffuse white, I would recommend krypton as a starting point. At low pressures and low power, this pretty much describes what it does.

I have a question for you. Or maybe more for your glassblower. I'm curious what it costs a professional to assemble an electrodeless tube or flask akin to what I have been using. Albuquerque's only commercial scientific glassblower is retired now I think. As useful as my developing skills in this area are, I wouldn't say I've mastered it by any means, and I'm just curious if the cost of getting the skilled glasswork done would be an attractive alternative to developing a refined personal capability in all of the construction of these things. If you can shed any light on this, I'd be grateful.

-Carl

Sigurthr

Wed Feb 27 2013, 11:47PM

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

Sure, I had Ron Soyland, who makes vacuum tubes, make my 1.25" OD pyrex tubes from pyrex stock. Most of the cost was labor, but still the glass itself was pricy. His glass lathe only accepts tubes up to 11" so my tubes are all 10" long. It came to about $85/tube for the 1.25" x 10" variety. He did not charge for fill gas since he has a ready supply of He, Ne, N, and Ar. I think he said any exotics would be a several hundred dollar investment for even the smallest gas flask. If you would like I can put you in contact with him, he is very knowledgeable.

Carl A. Willis

Thu Feb 28 2013, 12:54AM

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

I would like to get to know Ron and any of the other folks you alluded to.

I think there ought to be a wider collaboration on this stuff. What I would like, ideally, is a relationship with some local, skilled artistic glassblower who can actually make beautiful glass. The glassblower would envision and realize suitable containers for plasma, and then I could apply my technical repertoire with the gas filling and electrification. Best of both worlds, and the results could be truly sick.

My own expenses for this hobby come out in the $25-$30 range per tube or flask in glass and consumables, not including the equipment to make the pieces. The gas fill itself barely registers, except for a couple high-pressure, high-volume tests with xenon. As I have mentioned before, the cylinders rather than the gas are really what costs so much and also what dictate the requirement to buy certain quantities of gas. A large operation would spend almost nothing on gas, relative to the glassblowing.

-Carl

Wolfram

Sat Mar 02 2013, 01:42PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Have you seen the plasma sculptures by Mundy Hepburn

? He has some really interesting gas mixtures and he makes some beautiful tubes. I talked a bit with him earlier, and he mentioned that nitrogen was essential for the green color, like you found out. Here's one of his patents

, with some good info on some gas mixtures.

Carl A. Willis

Mon Mar 04 2013, 07:09AM

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

Mundy's work is gorgeous. But I can't help my skepticism about the sheer complexity of some of his mixes according to the patents--what role does each gas play, and does he really know? I have helium here at the house and it's not something I'm comfortable with in a plasma lamp. After all, it diffuses through Pyrex quite rapidly!

Anyway, here are a few more of my own experiments:

This is a 1-liter flask with
Xe: 20 torr (provides the basic structure, color, and brightness of the filamentary arc; produces the green tips in concert with trace N2)
Ne: 135 torr (subtle influence, considering the high pressure. Adds red color at the periphery of the glow.)
O2: 5 torr (important to the structure and flow kinetics, and has almost no influence on color)
N2: <0.1 torr (green color. Too much N2 results in a pinkening and fuzziness of the filament)

This is a 1-liter flask with
Xe: 40 torr (filamentary arc; green with N2)
Ne: 230 torr (subtle color and texture influences)
N2: 18 torr (major structure and color influences)

This is a 1-liter flask with
Xe: 35 torr (filamentary arc)
Ne: 136 torr (peripheral color and texture)
O2: 5 torr (major texture influence, no color influence)

-Carl

Ash Small

Mon Mar 04 2013, 10:38AM

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

Carl A. Willis wrote ...

I have helium here at the house and it's not something I'm comfortable with in a plasma lamp. After all, it diffuses through Pyrex quite rapidly!

That's an interesting comment. I'm fully aware that Helium will leak through most things, presumably due to it being monatomic, making it the smallest gas molecule, but a quick look at google suggests that the most common gases used in commercially produced plasma balls seem to be Helium/Neon mixes (Neon produces the orange-red, and Helium the blue).

,or.r_gc.r_pw.r_qf.&bvm=bv.43148975,d.d2k&fp=c25e4 5b6675ac0af&biw=1366&bih=663

Although Wikipedia states that Helium will leak out, Most other web pages (including two articles on the University of Illinois website) state that helium is one of the most common gases used.

Is it just a popular and widely believed mis-conception that Helium is a common gas in plasma spheres, or is this actually the case?

Steve Conner

Mon Mar 04 2013, 11:47AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I've never heard of plasma globes having helium in them. It's expensive and it would leak out.

Wolfram

Mon Mar 04 2013, 04:29PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Helium is not that expensive compared to any of the other gasses used in the tubes, except for argon and nitrogen of course. Xenon is hundreds of times more expensive.

From my discussions with Mundy, I got the impression that one of his main objectives is to make tubes that last for tens of years with continous usage, and some of his older tubes (20 years or so old) are still working. I'll ask him if he has had any trouble with helium diffusion through the glass the next time I talk to him. He specifically mentioned that organics and oxygen don't last very long in tubes (not together of course). Also, helium is used in HeNe lasers, and while I've heard stories of laser tubes becoming helium-deficient at old age, it doesn't seem to be a common problem. I also guess it depends on the partial pressure of helium, and this is a lot lower in his compositions than in HeNe-tubes.

I think every gas has a special purpose in his mixtures, I know that all of his gas compositions are made to work well at high pressures, for safety reasons. When I asked for details on the different gases, he explained in detail what effects each gas had at different partial pressures. I'll check with him if it's OK for me to reproduce this info here. I don't like being secretive about anything related to science, and he certainly wasn't when I asked him for details, but since he's spent over 20 years perfecting his mixtures, I'll check with him before reproducing it publically.

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