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Ash Small

Sat Mar 30 2013, 11:18PM

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

klugesmith wrote ...

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):

There was a thread here recently, I'll try to find the link EDIT:

Conundrum

Sun Mar 31 2013, 03:04PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Fascinating re. spherical discharges.

It almost looks from the video that these are collapsing toroids, does this only happen with xenon or does it happen with other gases?

-A

Wolfram

Mon Apr 22 2013, 09:55PM

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

I found an interesting document regarding Helium diffusion through glass a few days ago, while looking for something completely different. The effect of exposure to helium on photomultiplier performance and lifetime. What surprised me the most was the huge difference between the different types of glass. I quickly redid some of the calculations with parameters more relevant to plasma tubes, a 750mm long 50mm diameter tube with 1mm wall thickness. With a partial pressure of 10 torr of Helium, it takes tens of thousands of years for half of the Helium to diffuse through the glass in the case of standard soda-lime glass. High-borate borosilicate would lose half of the Helium in around 40 years in the same setup, and standard 7740 would lose half of it in only around 5 years, according to my calculations.

As for my own progress, there's not too much to report unfortunately. Acquiring vacuum equipment here has turned out to be much harder than expected, and now I'm considering bringing some vacuum equipment with me here the next time I go home for a visit.

klugesmith

Tue Apr 23 2013, 12:31AM

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

Re. helium diffusion through glass(es).

1. AFAIK that's the basis of portable "standard leaks" used to calibrate helium-sniffing leak detectors. You can make a glass ampoule that "leaks" at, say, 1e-5 standard cc/minute, with a decay rate measured in percent per year.
[edit] Glass permeation is one way to do it, and typically brings a tempco of +3% per degree C, according to

2. Something else I've heard but never tried.
If a sealed HeNe laser tube gets old from loss of helium, can it be rejuvenated by putting the whole tube inside an enclosure with any old helium at about 1 atmosphere?
If the laser tube likes an internal pressure of about 1 torr

then 1 day of inward diffusion should compensate for more than 2 years of outward diffusion.

Glass temperature is probably an important factor here. [as Shrad mentioned in this thread]

3. FWIW, I've observed that carbon dioxide diffuses out of inflated latex balloons as fast, or faster, than does helium. In the case of CO2 I'm guessing that it's a polar molecule thing.

Sigurthr

Tue Apr 23 2013, 02:47AM

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

I too heard about regassing He depleted HeNes by applying external helium... only the version I heard was several atmospheres while baking it at around 200C. Maybe they both work and one way is just very much faster?

Wolfram

Tue Apr 23 2013, 05:09AM

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

The temperature dependence on the diffusion rate is well described in the document I linked in my last post.

Carl A. Willis

Tue Apr 23 2013, 05:26AM

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

Here's a video featuring some neon mixtures. http://youtu.be/A9ECEGs_r2U

I'm particularly fond of the effects created by adding a trace of solid 1-bromo-3-chloro-5,5-dimethylhydantoin (spa oxidant) to the tube. Really brings out a great filamentary arc with some iconic red and orange neon colors. However, I don't have a good understanding of the mechanism behind this improvement. I think it is probably most related to the presence of trace halogens from decomposition of the solid, but the presence of CO / CO2 from the solid may also play a role. In any case, the longevity of any tube featuring an organic dopant is a major concern and, while this one has survived several hours of operation over about two months of existence without any noteworthy changes in behavior or ugly residues in evidence, I don't know what the long-term prognosis for it is.

Enjoy!
-Carl

Sigurthr

Tue Apr 23 2013, 07:09AM

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

Thank you, Carl! That was quite informative and enjoyable. Based on similarities between my high pressure neon tube and the second tube in the video I would wager there is some trace oxygen in my tube. The filament is a briliant white with orange/pink edges. The glassworker I had make it had no access to Xe, N, or Kr, so we can rule them out.

I look forward to more!

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