Plasma Toroid

[klugesmith]

Very nice. I would call that a toroid.

[davekni]

Alan:  Very interesting experiments even if not fully "successful"!  I'd guess that sodium or potassium would require the assembly to be in an oven or have a double-wall glass bulb with vacuum between walls and IR-reflective coating as with low pressure sodium vapor lamps.

I also killed my driver since at points I was inputting over eight amps. It probably indicates that my circuit
 is not tuned to best class E operating point.

Could be just excessive FET current or voltage.  Class-E FET current can be much higher than supply current.  FET conducts resonant current besides supply current.  Could also be excess FET gate power (internal gate series resistance) or overall power, since using a FET designed for much lower frequency.

[alan sailer]

I liked the experiment. It was not too hard to do and I got lots of pretty colors.

And yes I was pondering the ways and means of making a big globe without the condensed metal.
It was easy to see that I would need a hot globe inside a vacuum insulated visual globe. While
technically possible it would be a challenge to build with the additional problem of avoiding metal.
The oven is the best idea since it would help shield that noisy 10MHz.

And kludgesmith, although technically a torris like object I'd rather call it a lavender rosary. Hopefully other,
more explicitly religious pareidolia will not appear in the future.

[Uspring]

I don't classify it as a ring like the one you see in xenon since the brightening is not there and the rind is
beaded.

Yes, striations are typical of glow discharges. These occur in cold plasmas. The Xe toroid is one of hot plasma.
Presumably you would see much less power draw from the glow discharge, i.e. the 2500 Vpp you measured at the coil would not drop to 1000 Vpp as you saw with Xe. Also the light spectra would be continuous in the Xe case, as in thermal black body radiation, whereas you'd see line spectra in the glow discharge case.

[alan sailer]

So I have been going through my back catalog of plasma globe and got a few more interesting results.

First off is a globe filled with40 torr of xenon with a trace of iodine. Iodine turns all the noble gasses blue, different hues but all basically blue. This was the first time that I got a stable toroid above the coil.

https://www.flickr.com/photos/8763834@N02/52748239841/in/dateposted/

The second globe is a fill of 30 torr of xenon with traces of oxygen and nitrogen. this is the classic way to get a green plasma. the toroid is stable only with the coil on top.

https://www.flickr.com/photos/8763834@N02/52748650440/in/dateposted/

Finally a repeat of a globe with only xenon at 50 torr. It has the coil at the bottom and has the wonderful "smoke ring effect".

https://www.flickr.com/photos/8763834@N02/52748483559/in/photostream/

I am still trying to figure out why none of the globes I have recently filled with xenon will form a toroid. I have globes filled with the classic 15 torr that everyone is using for their toroid experiments and nothing happens. i also filled a globe with 50 torr and nothing.
i even have an old xenon globe at 110 torr that I can get a toroid.

I just ordered parts to try a Steve ward toroid driver using an FDA18N50. The only major difference I can see with this driver vs the one I am using is 2 turns vs 3 turns on the drive coil.

I'd like to get a stable 15 torr globe working for use as a permanent display. So far as I can tell people are getting the 15 torr toroid to run without a kicker coil to start ionization.

Cheers.

[davekni]

Nice videos as usual.  Enjoy watching your experiments.

So far as I can tell people are getting the 15 torr toroid to run without a kicker coil to start ionization.

Many of the videos I've seen still require at least capacitance to ground of a hand on the globe (or fill tube end) to start an arc.  It appears that starting is usually due to electric field capacitively coupled through the glass wall.  Perhaps a bit of grounded foil against the globe somewhat close to the coil would be sufficient to use coil voltage for starting.  Or perhaps a grounded spiral or other non-closed shape of wire against the globe surface would be best, providing sufficient capacitance while blocking less magnetic field.  Optimum size for added grounded electrode probably depends on glass thickness and location.  Guessing perhaps 10x glass thickness away from coil wire.  Diameter depends on whether trying to maximize field at coil or at added electrode.  Small to start arc at electrode, large to start arc at coil.
This is something I hope to explore more eventually myself, but several projects are ahead of plasma toroid in my planned list.

[Uspring]

I'd like to get a stable 15 torr globe working for use as a permanent display. So far as I can tell people are getting the 15 torr toroid to run without a kicker coil to start ionization.

You might have an impedance matching problem with lower pressure. Ignition will require less voltage, but possibly the toroids resistance will be higher compared to your previous experiments due to the lower pressure. That might require extra turns to get enough power into the toroid to heat it up to plasma temperatures.