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Registered Member #1829
Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74
Does anyone know roughly at what pressure a discharge will form the layered plane shape seen here? He says he uses a two stage rotary pump but doesn't specify the pressure. I tried a similar experiment with a water aspirator and only got a solid (but pretty) glow.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Voltwad wrote ...
Does anyone know roughly at what pressure a discharge will form the layered plane shape seen here? He says he uses a two stage rotary pump but doesn't specify the pressure. I tried a similar experiment with a water aspirator and only got a solid (but pretty) glow.
That looks like he is using an HF AC supply and the "layers" are standing waves.
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
The positive column is nearly aways pink when evacuating an air filled discharge tube. The reason is, that as you evacuate the tube, waters vapour pressure starts to become significant. By the time the positive column appears, most of the air has been removed (oxygen-nitrogen), and most of the remaining pressure is due to water vapour. Serious backtreaming of oil vapour will turn the positive column from salmon pink to a dirty grey.
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
Here's what I think is going on:
The RF discharge that you're getting from your cap system doesn't put in as much energy as a straight discharge does. The energy of the plasma determines the color of the discharge to a point. The more energy, the more orbitals an electron travels through and thus the different frequency of light. Don't remeber the exact equations but that's why gasses have multiple discharge lines.
I tried doing what you did but couldn't get it to work... time for another try!
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
the light emission is the experimental proof of Faraday's law of induction (see maxwell equations: Maxwell-Faraday equation). When the magnetic flux density changes over time, the curl operator in the equation implies the generation of an electric field with closed, circular field lines inside the tube. (translation for german "Wirbelfeld", anyone?). I assume capacitive coupling to be negligible. So basically you ionise the residual gas inside the tube, its constituents are mentioned above. You will have some difficulty telling what emissions you observe by just looking at the color of the discharge, because molecules with complex emission spectra are involved. At lower pressures and higher current densities, spectra of highly ionised atoms may be observed.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
hboy007 wrote ...
the light emission is the experimental proof of Faraday's law of induction (see maxwell equations: Maxwell-Faraday equation). When the magnetic flux density changes over time, the curl operator in the equation implies the generation of an electric field with closed, circular field lines inside the tube. (translation for german "Wirbelfeld", anyone?). I assume capacitive coupling to be negligible. So basically you ionise the residual gas inside the tube, its constituents are mentioned above. You will have some difficulty telling what emissions you observe by just looking at the color of the discharge, because molecules with complex emission spectra are involved. At lower pressures and higher current densities, spectra of highly ionised atoms may be observed.
I'll try this myself soon ;)
Interesting stuff! I imagine that you might be able to learn quite a lot by looking at the light through a simple optical spectroscope.
Registered Member #1034
Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154
I tried doing what you did but couldn't get it to work... time for another try!
The only thing I found to be critical was the vacuum, in fact if I let the pump run too long the pump oil would heat up and it would stop working.
What is the frequency of the tesla coil?
I ran it though the Java script Tesla coil designer and came up with about 800 KHZ. I have used other coils with more and fewer turns and it doesn't seem to make much difference.
I should point out that if I run this thing for vary long the tube gets hot!
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
If your pump stops working when the oil heats up, something is wrong with your pump, or you have the wrong oil in it.
First off, I presume you have a rotary vane pump. You should be running a hivac pump oil eqivalent to Inland 19. Your pump should be able to run continuously and maintain vacuum when hot. Hopefully you didn't put automotive oil in your pump.
Do research on emission spectra of plasma used for optical endpoint in plasma etching (in the semiconductor mfg industry). There is extensive data available and should be easy to find.
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Pink light emission from low pressure gas lamp
