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Carl A. Willis

Tue Feb 12 2013, 07:22AM

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

Hello all!

I've lurked here extensively, I know many contributors here personally, but for some reason have been slow to join up. My usual habitat over the last decade-plus has been on the Fusor.net forum, where I share projects involving nuclear fusion and drop the ol' banhammer on the occasional troll in my administrative capacity. Today I have something to share that is genuinely more relevant to 4HV and not nuclear at all, just fun stuff involving decorative plasmas. I put together a small high-vacuum system based on a Pfeiffer TPD-20 drag pump, rounded up some surplus xenon and krypton gases, and did a little bit of glassblowing, and in the process I produced some electrodeless high-frequency discharge tubes that I thought were pretty enough to talk about. Any comments, advice, links to other efforts or further information would be much appreciated as I expand my repertoire in this area!

Already I'm indebted to this forum's own member, "zrg", whose plasma art has been discussed here and in his many dramatic videos on YouTube. He really has paved the way for my efforts.

I use a small high-frequency power supply of my own construction to excite these tubes. The supply consists of a little PWM-chip-driven mosfet half-bridge pumping a transformer from an old Glassman HV supply, with rewound primary and re-gapped core, and potted in mineral oil. Frequency is 10-50 kHz or so; maximum output can form an arc about 2 inches long in air. It is a more powerful and better-insulated supply than the 12-V powered version Bob Ianinni's Information Unlimited website sells, but I happen to know that those work quite satisfactorily for this job too. I typically will make the HV connection to the electrodeless tubes via a cup of water, itself capacitively linked to an underlying metal plate. This provides good, even electrical contact to the tube and helps naturally cool the glass where the dielectric barrier discharge is occurring.

Photos of my efforts are at the bottom. In order of appearance, here are the descriptions:

1. Xenon at 40 torr, with less than 1 torr of air added. Air is responsible for the greenish color at the ends of the filamentary arc. Specifically, I strongly suspect nitrogen alone is the green agent. Neither pure oxygen, nor CO2, nor argon, nor water will produce this color. Unfortunately I do not presently have a tank of pure nitrogen on hand. Air reliably produces the green, which I really like.

2. This is a 1-liter flask with Xe at 45 torr and again, a little bit of air for the green color.

3. At only 25 torr, Xe + trace air produces this gorgeous "fern" in a 1-liter flask. It is a very different effect from xenon's customary filament, but beautiful nonetheless.

4. Three 24-inch-long, 1.5-inch dia. pieces or borosilicate tubing filled with different gas mixtures. My hand (at bottom) is touching a tube with pure krypton at 200 torr. Even at this high pressure, krypton does not completely form filaments; there are diffuse zones in the arc. It is also hard to ignite the discharge. In the middle we have a xenon / air tube filled to a total pressure of 30 torr. At the time it was made, I had not identified air as the culprit behind the emerald green; I had a leaky valve seal that ultimately became known and led to the understanding. The partial pressure of air is under 1 torr. And finally, at the very top: Krypton at 100 torr plus elemental iodine at its equilibrium vapor pressure (~0.3 torr). Note the contrast with the pure krypton tube. The iodine makes the discharge much more concentrated and filamentary even at lower pressures, and it adds a very appealing blue color. Iodine's own discharge is NOT blue at all, but rather a greenish-yellow color! Iodine adds no discernible benefit to an argon discharge. It only adds this striking blue to xenon and krypton fills.

5. This last pic just shows my vacuum pumping system with a 1-liter flask attached. I can add up to three gases to the manifold as presently configured. There is a 1000-torr capacitance manometer for accurate, gas-independent pressure measurement. I have xenon and krypton that I got surplus (Xe dates to 1962!), and I ordered a tank of neon (present cost in 250-liter quantity is about $0.68 per liter from Matheson). It will take several more weeks to get here probably.

Finally, I'll drop in a link to my YouTube channel, where I show a variety of plasma effects in my recent uploads. These plasma effects really need to be seen in videos to be fully appreciated.
http://www.youtube.com/user/Thallium208

Thanks y'all for your attention and any contributions to this thread will be much appreciated.

-Carl

Physics Junkie

Tue Feb 12 2013, 08:13AM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

Lovely work. I like the second one a lot

macona

Tue Feb 12 2013, 08:26AM

Registered Member #3272 Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101

Where did you find the xenon and krypton gasses? I am planning on attempting to extract the gas from used high pressure xenon arc lamps.

Conundrum

Tue Feb 12 2013, 08:48AM

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

Hi, have you considered making some demo "not fusing" He filled fusors for educational purposes?

Maybe add extra gases to highlight field lines etc.

-A

Ash Small

Tue Feb 12 2013, 09:08AM

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

Nice work Carl. I noticed what looks like an oxy-propane torch in the last photo.

Is it simply a question of heating the glass tube and twisting to seal?

I'm sure others here would appreciate a bit more detail regarding the glassblowing techniques involved.

Is borosilicate the best type to use for this application?

(You've come over to 4HV to pick up some tips on moderation, I presume?

)

macona

Tue Feb 12 2013, 02:30PM

Registered Member #3272 Joined: Mon Oct 04 2010, 11:40PM
Location: Beaverton, OR
Posts: 101

Ash Small wrote ...

Nice work Carl. I noticed what looks like an oxy-propane torch in the last photo.

Is it simply a question of heating the glass tube and twisting to seal?

I'm sure others here would appreciate a bit more detail regarding the glassblowing techniques involved.

Is borosilicate the best type to use for this application?

(You've come over to 4HV to pick up some tips on moderation, I presume?

)

To seal the glass you soften the glass and push it together a bit to thicken. Once the glass is soft enough it will collapse in on itself from the vacuum. Then you can pull it apart. You have to be careful when parting so it does not blow through.

Boro is good but you need oxygen to work it. You can also get leaded glass for neon signs, that can be worked with fuel-air. I just ordered some today for a project from glasscraftinc.com. You can buy single sticks of Simax boro in lots of different sizes.

Steve Conner

Tue Feb 12 2013, 02:59PM

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

Nice!

I had a commercial plasma ball that turned green as it aged (and took hits from Tesla coils) and I always wondered why this happened. Looks like nitrogen from an air leak then.

Carl A. Willis

Tue Feb 12 2013, 07:40PM

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

macona wrote ...

Where did you find the xenon and krypton gasses? I am planning on attempting to extract the gas from used high pressure xenon arc lamps.

The krypton cylinder is almost empty and was being thrown out at work, with about 40 psig remaining (about 20 liters in this particular cylinder). The xenon I purchased from a local guy who had a lecture bottle sitting in storage. It was manufactured in 1962! The cylinder still had about 23 liters in it.

For reference, I did ask for quotes on various gases. For this application, not much gas is used, and a lot of the expense instead has to do with the cylinder and the HAZMAT shipping of it. Matheson's prices on neon and xenon, NOT including the cylinder, which must be rented or purchased (~$350):

250L Neon, UHP purity = $168.35

250L Xenon, 5N research purity = $3830.00

250L Xenon, "Matheson purity" = $2608.50

SpecGas, Inc.'s prices for disposable, non-refillable cylinders (cylinder price included):

100L Neon = $350

100L Krypton = $600

100L Xenon = $850

These are expensive gases to be sure, but happily the amounts used in any single plasma toy are very small. The real risk is accidentally wasting gas through valve mishandling or other accidents!

-Carl

Conundrum

Tue Feb 12 2013, 08:09PM

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

Wonder if there is much xenon in an old linear flash tube from a few defunct ancient flash guns?

Wolfram

Tue Feb 12 2013, 09:08PM

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

Those tubes are stunning.

I was also inspired by zrg's tubes and I've started putting together a vacuum system for making gas discharge tubes. I still have some work to do though, vacuum parts and gases are hard to get here, and I have to import everything from the US. Also, I'm going to CERN for a year, and I'm moving in two weeks so it doesn't look like I'll get any tubes made before I leave. If surplus vacuum stuff is easy to get there, I might be able to put together a vacuum system and make some tubes while I'm there.

I'm interested in some more info on your gas delivery system. Do you have any close-up pictures?

Regarding gas prices, I found Advanced Speciality Gases to have bette prices than any of the other vendors I got quotes from. All prices are 5N purity, including a disposable cylinder and CGA580 valve and excluding shipping. They also seem very hobbyist-friendly.

Xe 200l $2,585
100l $1,435
50l $835
25l $535

Kr 200l $635
100l $435
50l $360

Ne 500l $460
200l $385
100l $310
50l $235

Also, Tecnolux sell disposable low pressure cylinders (with 12l of gas) that are easier to work with. The containers are 1l and the pressure is 12 bar.

Xe â‚¬708
Kr â‚¬118
Ne â‚¬67
Ar â‚¬61
He â‚¬ 67

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