Author Topic: Plasma Toroid  (Read 1565 times)

Offline Uspring

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Re: Plasma Toroid
« Reply #20 on: November 08, 2022, 04:29:37 PM »
Thank you, klugesmith. That calculation depends on an assumption about the diameter of the hot region of the torus and I really don't know that, My very first calculation based on some tabulated heat conduction values from the internet came out to 3600 K and I thought, wow, that looks reasonable and I didn't try to improve the estimate. I don't have literature values on plasma conductivity for Xe, but for the ones I have, e.g. for air and Ar at 1 bar, it seems temperature should be somewhat higher, like 5000+ K. So that's all a bit ballpark. In any case, we are dealing with hot plasma here, not a neon sign type glow discharge.

Offline alan sailer

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Re: Plasma Toroid
« Reply #21 on: November 08, 2022, 05:41:18 PM »
David,

I have read and thought about your three heating ideas.

The first I don't understand the insulation comment. Do you mean that that copper in the center doesn't conduct any electricity.

The second explanation makes great sense. To state it another way, the current does not stay in one strand but has to travel from one strand to another. The contact resistance between strands heats up the wire more.

The solid wire I tried (it's insulation failed) was 14AWG 1.55mm diameter. The stranded is 12AWG 19 strands each 0.4mm. Both are unplated solid copper.

Offline davekni

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Re: Plasma Toroid
« Reply #22 on: November 09, 2022, 04:31:48 AM »
Quote
The first I don't understand the insulation comment. Do you mean that that copper in the center doesn't conduct any electricity.
Center current isn't zero, but extremely close to zero.  True for both solid and stranded.  Skin depth is about 20um at 9.8MHz.  Current drops exponentially from outer edge of copper inwards.  12AWG wire is 2mm diameter, 1mm radius.  By the center current is exp(-1mm/20um) lower than the edge.  Actually, that's a formula for flat conductors.  Not sure off-hand the difference with round.  Doesn't matter much here.  Center current density is ~1E-20 of outside.  Extremely low, even if incorrect by an order of magnitude or two.

19-strand wire is likely to keep the same 12 wires on the outside, at least mostly.  1 center, 6 around that, and 12 around those.  If so, and given unplated copper, stranded loss is likely due to limited copper at outer 20um of wire circumference.  Can't think of any other likely reasons.  Perhaps someone else will.
« Last Edit: November 09, 2022, 09:05:28 PM by davekni »
David Knierim

Offline alan sailer

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Re: Plasma Toroid
« Reply #23 on: November 09, 2022, 06:47:49 PM »
David,

Thanks for the reply. It's not of any real importance. I was just curious.

I'm an OK engineer as I can usually either figure out stuff or find someone (person or book) that
gives the answer.

I'm also sort of fixated on results, so if something doesn't work well (hot stranded wire) and I find
something that does (cooler solid wire ) I generally just go forward without trying to understand
why.

Offline davekni

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Re: Plasma Toroid
« Reply #24 on: November 09, 2022, 09:19:09 PM »
There's lots of information available on "skin depth", an important consideration for many if not most AC circuits.  Even at Tesla coil frequencies, copper skin depth is ~0.2mm.  Typical copper tube primary conductors are using only outer 0.2mm of the tube.  At 60Hz line frequency copper skin depth is ~8mm, so matters only for large high-current bus bars.

BTW, edited my last post to fix the exponential formula.
David Knierim

Offline alan sailer

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Re: Plasma Toroid
« Reply #25 on: November 20, 2022, 01:27:00 AM »
Today I felt better than I have for a long, long time so I have been playing in the garage. I set-up the xenon plasma globe and blew some plasma (smoke) rings. The camera taking the video is an old Edgertronic unit that is running at about 2000FPS.

https://www.flickr.com/photos/8763834@N02/52511116424/in/photostream/

I took another video with the coil on top, which creates a stable toroid. When I stepped the video you can clearly see that the tendrils snake about until one happens to meet up with another and create a closed circuit. The ring flashes into existence and quickly tightens up into a circle. It's fascinating to watch.

Offline davekni

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Re: Plasma Toroid
« Reply #26 on: November 20, 2022, 05:08:31 AM »
Absolutely fascinating!  Thank you so much for sharing.  Happy that you are feeling better too.
David Knierim

Offline alan sailer

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Re: Plasma Toroid
« Reply #27 on: November 28, 2022, 12:06:02 AM »
I decided to break out part of my old plasma filling system (valves, pumps, gauges etc) and try out different gasses with the
10MHz oscillator. After the usual reeducation ("leaks" are sometimes just out-gassing) I got the system set-up and pumped to 30mT.
I'm using a 1000ml round flask with a 24/40 ground glass joint. This lets me set-up and run without waiting months for real glass
from a glassblower. The gauges are two Baratron 10 and 1000torr. I used a Convectron to calibrate them years ago so they are probably OK. At least they agree in the crossover pressure.

I tried three gasses in the range from 50 to 1 torr air (cheap), argon and neon. The 10MHz oscillator was set at 19V/3Amps. I used the vacuum leak oudin coil to start things up. Also played with the current up to 5 amps. I could not find any toroid formation in any of these gases.
I have one left to try krypton but have not found the tank yet.

I am also planning to try the set-up with sodium and potassium. I'm hoping that the path between the globe and the gauges is long enough that the metals can condense out and not hurt anything.Evidently under vacuum these metals when heated moderately can vaporize enough to ionize. They both have such low ionization potentials that they may do something interesting with the oscillator.


Offline klugesmith

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Re: Plasma Toroid
« Reply #28 on: November 28, 2022, 02:09:06 AM »
Glad to hear stories about digging out old playthings.  Can you produce conditions today that are similar to those in your old sealed bulbs that do display toroids?

Regarding the metals, for example sodium.    We know that sodium vapor lamps are filled with rarefied Ne or Ar to get the arc started and warm things up.    Partial pressure of metal vapor can never exceed equilibrium where it condenses at coldest place on vessel wall.   
So I bet the atom fraction in low pressure sodium lamps is never more than 0.1% metal, but for some reason that generates most of the light.  Like Hg in regular fluorescent lamps and non-red neon lighting:   a few microns of Hg pressure and many torr of inert gas pressure.

OTOH, Hg vapor rectifiers with hot cathode manage to ionize at 10 or 15 volts.  As far as I know, the gas content is nothing but Hg vapor, at pressure than can't be more than a few microns.
« Last Edit: November 28, 2022, 02:44:52 AM by klugesmith »

Offline davekni

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Re: Plasma Toroid
« Reply #29 on: November 28, 2022, 03:26:55 AM »
Quote
I tried three gasses in the range from 50 to 1 torr air (cheap), argon and neon. The 10MHz oscillator was set at 19V/3Amps. I used the vacuum leak oudin coil to start things up. Also played with the current up to 5 amps. I could not find any toroid formation in any of these gases.
I have one left to try krypton but have not found the tank yet.
Thank you for for the experiments and results!  I would have expected argon to form a toroid as easily, just not be as bright as xenon.  I think dielectric strength of argon is slightly lower than xenon at any given pressure.  Must be some other characteristic hindering toroid formation.

Quote
We know that sodium vapor lamps are filled with rarefied Ne or Ar to get the arc started and warm things up.    Partial pressure of metal vapor can never exceed equilibrium where it condenses at coldest place on vessel wall.
My small (perhaps 800mm, bent into a U, so 400mm long) low-pressure sodium vapor lamp is in a double glass housing.  Inner U-bent tube surrounded by a larger cylinder glass cover for thermal insulation.  I'm not sure if the space between glass walls is vacuum or filled with some low-thermal-conductivity gas or vented to atmosphere.  It takes a long time (20 minutes) to warm up to full brightness.  Initial glow is just the noble gas color.  There is a tiny bit of the noble gas colors remaining at full brightness, but sodium lines are orders-of-magnitude stronger (by visual judgement through a diffraction grating).  I'd guess that the sodium pressure is significant at full brightness, probably higher than that of the starting gasses.
David Knierim

Offline klugesmith

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Re: Plasma Toroid
« Reply #30 on: November 28, 2022, 05:21:37 AM »
It looks like Dave and I are in the small club of people with big LPS lamps at home.  In my case, parking lot luminaires that were replaced with LED's.  The only voltage taps on these ballasts are for 208 V and 277 V.  I haven't observed the spectrum, but this outdoor picture on a sunny day in 2018 gives an idea of the luminance.

Dave, do your lamps (SOX series ?) have little dimples at intervals along arc tube, as intentional cold spots for sodium to go when lamps are off?

Following up on my guesses about vapor pressure, Internet search found this familiar classic chart.
https://www.powerstream.com/vapor-pressure.htm
Suggests that tube must be pretty darn hot to get sodium pressure higher than 1 micron.

There's an old stubby version, the NA-1 lamp, once used as a laboratory light source.  Normally operated inside a double-wall vacuum Dewar to get hot enough at 5W or 10W power level. http://lampes-et-tubes.info/dlna/dl074d.jpg

We could compare elements' vapor pressures at their normal melting points.   Zn and Cd are familiar as "volatile" in that sense, and noted in high-vacuum literature.   Hg, Pb, and I think Na are in bottom quartile.  In and Ga are in a class of their own at the bottom of vapor pressure charts (at their respective melting points) IIRC.

[edit] found one reference giving tube temperature.
http://www.soxlamps.org/soxdiagnostics_contents.htm
4. Failing to warm up fully to final colour — i.e. more orange or red than normal
If the lamp does not reach its optimum operating temperature of 260°C, the sodium inside may not vaporise and the red colour of the neon in the lamp tube would be the result. This is normally attributable to a leak in the outer jacket: when the outer vacuum fails, the thermal insulation of the arc tube deteriorates, and the lamp can only partially warm up. ... (ref: Colin Grimes, James Hooker, Mike Docherty)

260 °C is 533 K, where Honig chart shows sodium at 5 microns vapor pressure.
I think that what counts is the temperature of coldest spot on tube wall.   But maybe non-uniform partial pressure along the length of an arc tube can persist for a while.  I guess neon lamp tubes and curly CFL's charged with Hg can take minutes to get uniformly bright.  How can diffusion timescale be more than a few seconds, in 1 meter length of hot and rarefied gas?
« Last Edit: November 28, 2022, 08:12:21 AM by klugesmith »

Offline Uspring

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Re: Plasma Toroid
« Reply #31 on: November 28, 2022, 06:01:14 PM »
I believe, that the gases you used are too thermally conductive, requiring more power than available to sustain a hot torus. Possibly you could see a self sustaining glow discharge at the lower pressures. But these were cooled too well to reach the lower limit temperatures of hot plasma conductivity (4000 - 5000K). Or the gas was too dilute to be able to carry much current.
I think you have a better chance of success with Krypton, which is less thermally conductive than Argon or air. Or you increase amp turns of your coil.

I really liked the slow motion video. Pretty and interesting. It looks like the torus flashes brightly initially. Difficult to explain.

Offline kurtrox

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Re: Plasma Toroid
« Reply #32 on: November 29, 2022, 05:51:59 AM »
Good evening Alan! I too have joined in this quest to make shiny bright xenon donuts, I finally received my 2L 15Torr xenon envelope (sphere). I am currently only using the basic 10Mhz oscillator (SSTC) from teslundmehr on youtube flame candle design. I am having extreme difficulty keeping my variable bench supply calm from some sort of back EMF. or RF noise. I also keep killing the IRFP460 and IRFP260 Mosfets I'm trying to use. I would love some help shedding some light on your circuit design.

https://www.circuit-diagram.org/circuits/24ddc75d2c05422cb0dfbe5f598448c6

I have chosen to use 2x 1KOhm Resistors and only a 4.7nf and also tried a 5.6nf capacitor once that is in parallel with the TVS. I will admit, I was super excited to make the flame candle work, and then the globe, but I would really like to get it to run a bit longer ( i do have the mosfet heatsinked and fans). Any help would be appreciated.

I am super new to the idea of winding my own coils. I have tried to get as close as possible winding my own magnet wire around small pieces of plastic tubing. I know the plastic effects things but unclear as to how much, I see your coil on the glass is directly on the globe, and also the windings are bundled. Does this help performance? Thanks!

I forgot to mention some other information. I have tried to get the toroid to form at 19v as suggested by other people doing similar things, but Ive only been able to get tendrils to form. I can achieve a toroid at 30V and roughtly 3 amps.
« Last Edit: November 29, 2022, 05:57:12 AM by kurtrox »

Offline alan sailer

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Re: Plasma Toroid
« Reply #33 on: November 29, 2022, 04:08:00 PM »
kurtrox,

I'm sorry that you are having such problems. I used the exact same diagram that you linked to and it worked on turn-on.

I happen to own an LCR meter so measuring the coils was easy and accurate. Plastic is an ideal coil form and should have no effect on the inductor unless you are using some weird plastic. PVC tubing works great.

If the MOSFET is heating too much then the circuit is probably not operating class E and needs to be tuned.

I bundled the output coil because I wanted to keep it somewhat neat. Keeping the coil bundled does affect the inductance somewhat.

Is your coil running at 10MHz? How are you establishing the inductance? You can measure an unknown inductance be resonating it with a known capacitance...

Offline davekni

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Re: Plasma Toroid
« Reply #34 on: Today at 04:51:33 AM »
Looks like Kludgesmith is correct about relative pressures.  On the order of 1000Pa for noble fill gasses and 0.4Pa for sodium vapor.  Found another reference:
http://www.lamptech.co.uk/Documents/SO%20Vapour.htm
http://www.lamptech.co.uk/Documents/SO%20Gas.htm

Quote
I believe, that the gases you used are too thermally conductive, requiring more power than available to sustain a hot torus.
Good point.  I hadn't thought about thermal conductivity.  Some day, after many other projects on my list are past, I hope to try argon with higher field strength.
David Knierim

Offline DashApple

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Re: Plasma Toroid
« Reply #35 on: Today at 07:37:22 AM »

Dave, do your lamps (SOX series ?) have little dimples at intervals along arc tube, as intentional cold spots for sodium to go when lamps are off?


I have a few newer lamps in the 55W to 180W range with the dimples, I think one reason for them is they are there to provide more even distribution of sodium during the warmup phase on the longer tubes and perhaps a longer life,  after enough time the sodium in the dimples will go and never come back .

Some of my older 135W lamps lack the dimples and the sodium sits in the U at the lamp top

Offline klugesmith

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Re: Plasma Toroid
« Reply #36 on: Today at 09:35:18 AM »
Thanks for dimple observations.  And thanks to Dave for showing us that website, with a wealth of details about a lamp technology that filled an important niche for more than a half-century.  Check out the page about sodium migration.   It confirmed that sodium partial pressure can differ substantially from place to place along the tube.  I guess the conditions make diffusion very very slow (for a gas).  Site includes this picture of a demonstration lamp whose heat-retaining coating was removed from right half of arc tube. Outer envelope is warm in left half and hot in right half.


I respect the site's choice to report pressure values in pascals. 0.4 Pa is very close to 3 microns.
In olden days, the exact conversion factor would depend on density of Hg at some temperature, and acceleration of gravity at some place. Now it's easier to remember:
Torr is defined to be 1/760 standard atmosphere. Standard atmosphere is defined to be 101325 pascals.
Hmm, I bet the 101325 was adopted to reasonably match 760 mm of mercury in centuries of barometric instrumentation.

Back to nominal subject of this thread: I guess Alan has his work cut out for him. Get back to xenon wrangling and demonstrate a sodium-doped plasma toroid. :)
« Last Edit: Today at 10:12:50 AM by klugesmith »

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Re: Plasma Toroid
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post Re: Welcome new members, come say hello and tell a little about yourself :)
[General Chat]
AkashaStar
November 19, 2022, 01:56:10 PM
post Re: Buck converter question
[Dual Resonant Solid State Tesla coils (DRSSTC)]
dru
November 19, 2022, 08:03:56 AM
post Re: Induction cooker without electronics
[Electronic Circuits]
Solhi
November 19, 2022, 06:38:00 AM
post Basic Gate driving doubts
[Solid State Tesla Coils (SSTC)]
prabhatkumar
November 19, 2022, 05:37:09 AM
post Re: ZVS driver won't oscillate
[Electronic Circuits]
davekni
November 19, 2022, 03:59:56 AM
post Re: Non-laser pointer
[Light, Lasers and Optics]
klugesmith
November 19, 2022, 03:56:32 AM
post Re: Buck converter question
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
November 19, 2022, 03:36:20 AM
post Re: Vacuum pump
[Laboratories, Equipment and Tools]
davekni
November 19, 2022, 03:26:48 AM
post Re: Vacuum pump
[Laboratories, Equipment and Tools]
Alberto
November 19, 2022, 12:40:33 AM
post Re: ZVS driver won't oscillate
[Electronic Circuits]
AstRii
November 18, 2022, 09:32:33 PM
post Re: Induction cooker without electronics
[Electronic Circuits]
klugesmith
November 18, 2022, 05:48:00 PM
post Re: Audio Modulated CRT Flyback Transformer Loud Sparks
[Transformer (Ferrite Core)]
John123
November 18, 2022, 03:49:12 PM
post Re: TV flyback number of primary turns rule of thumb
[Transformer (Ferrite Core)]
John123
November 18, 2022, 02:56:49 PM
post IF D95T vs IF D95OC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
RoamingD
November 18, 2022, 01:44:38 PM
post Re: Induction cooker without electronics
[Electronic Circuits]
Solhi
November 18, 2022, 11:38:44 AM
post Non-laser pointer
[Light, Lasers and Optics]
klugesmith
November 18, 2022, 10:05:29 AM
post Re: Induction cooker without electronics
[Electronic Circuits]
klugesmith
November 18, 2022, 06:54:55 AM
post Re: Induction cooker without electronics
[Electronic Circuits]
Twospoons
November 18, 2022, 06:29:23 AM
post Buck converter question
[Dual Resonant Solid State Tesla coils (DRSSTC)]
dru
November 18, 2022, 06:10:52 AM
post Re: TV flyback number of primary turns rule of thumb
[Transformer (Ferrite Core)]
davekni
November 18, 2022, 05:53:15 AM
post Re: Induction cooker without electronics
[Electronic Circuits]
Solhi
November 18, 2022, 05:21:52 AM
post Re: Vacuum pump
[Laboratories, Equipment and Tools]
davekni
November 18, 2022, 04:00:04 AM
post Re: Vacuum pump
[Laboratories, Equipment and Tools]
alan sailer
November 17, 2022, 10:24:35 PM
post Re: TV flyback number of primary turns rule of thumb
[Transformer (Ferrite Core)]
John123
November 17, 2022, 08:30:00 PM
post Re: TV flyback number of primary turns rule of thumb
[Transformer (Ferrite Core)]
klugesmith
November 17, 2022, 07:28:16 PM
post Re: TV flyback number of primary turns rule of thumb
[Transformer (Ferrite Core)]
John123
November 17, 2022, 03:38:00 PM
post Re: TV flyback number of primary turns rule of thumb
[Transformer (Ferrite Core)]
davekni
November 17, 2022, 04:03:51 AM
post Re: what type of diode is better for make high voltage diode?
[Voltage Multipliers]
davekni
November 17, 2022, 03:57:40 AM

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