Re: Color Fades in discharges

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Mike" <induction@xxxxxxxxxxx>

Hi Phil,
            A little further down the reply line is also one from Dave which I
will also address about electrode contamination and gas alteration by the
discharge. And another nice reply from Matt. Good points!
I considered, as you say, doing a gas elimination. As the fresh air
constant intake we used to work around the problem enters via an electric
valve then through two needle valves, dual for fine and rough, one with a
gravity ball flow gauge to help in range pre-sets, we have a fixed location
inlet. To that inlet, I had wished to place a plastic flexible bag of known
volume and add all but one atmospheric gas in the right ratio per test. I
hoped to do this one gas at a time, just as you advised but the metering
equipment for that is not available to duplicate an actual air ratio. We have
a small tank of dry N2 but none of the other gas except O2 from a torch.
We are working with MIT people on tube related studies but every favor
used up is one not available later. But we both agree this would be a good
pointer to what is happening, well, maybe. As Dave points out later in the
thread, this could be electrically bonding gas to other combinations.
There is another very good point you bring up, also as relates to streamer
extension tendency and this color / chemistry change problem. I think you
hit a magic button with lifetime of this "burned" gas as it exists in open air.
You refer to the impulse rate of coils. I will quote you here:
PHIL SAID " I think by our minimum BPS for long sparks that there's some
time-dependent effect that lasts only a few mS to allow the streamers to
extend. A lifetime of a "burnt" product in the air?" Close Quote there and
I think very intuitive on your part. In an email communication of just today
of which I was copied and related to this rise time, ionization path, luminance
and persistence of sprites, glowing discharges in the ~45 to 90 Km high
regions of the atmosphere caused by mainly positive cloud to ground strikes.
My friend Earle had this to say: "Regarding time scales, the lifetime (from 
Einstein
coefficients) for the N21PG transition is 6 usec (Heavner et al,  ??? and 
elsewhere).
Sprite luminous lifetimes are orders of magnitude longer, suggesting a 
quasi-steady
forcing which we now attribute to charge transfer by the parent lightning.
(A more appropriate time scale is the streamer lifetime, rather than the 
sprite lifetime,
so please provide some numbers here.)  The time scale for the charge transfer
in the return stroke is hundreds of usec (already much longer than the 6 usec
lifetime), but for sprites we are dealing with continuing current events 
with time
scales of 1000 usec plus." Ending Earle's quote. In the confines of the tube or
in the open air of your TC this forcing is the driving voltage. This 
ionization rise time
is as valid for lightening as it is for the TC or the enclosed tube at low 
pressure,
all cases are over volting of the gas. Just an issue of volts per inch to 
pressure ratio.
Take a coil that does say 3 feet, trap a streamer in a glass tube say 6 
feet or 4 feet
with end electrodes to encourage flow through and seal the tube up after 
you flood
the tube with ozone, does it go further? I assume ozone is the culprit 
here, initially.
(maybe?) Note those heavy strikes to conductors hardly stink up the room (until
after the show is over) while a tiny hand held kicker coil will run you out 
of the place
in no time. I think maybe sheathing is why. In the tube I get to watch it 
all the time.
(In the arc mode). Hot plasma channel forms, current density climbs, 
voltage driven
resistance drops, it would try to pull infinite current without ballast.
Cool plasma contains (sheaths) warmer plasma. Reducing pressure I've made
the discharge more constricted, placed amp meters at central point and other
current measuring meters at the outer sheath area. Amps center, miliamps at 
the sheath.
So the energy is shunted in the arc channel and little left to further 
ionize outside the
sheath. Big arc, less non-contained ozone or what odorous compound that is.
Small coil, low current, lots of low temperature streamers, not much sheathing,
not much shunting, lots of odor. High voltage, high Z, high stink. Looking 
at pictures
like the easy to zoom in on ones Terry put up of his TC lets you see some 
sheathing
~ straight brighter lines center, Blue slight twist outer. Unless it's 
camera saturation
but I do get to see this with ease at lower pressure and without camera assist.
The big fat arcs sheath well. That's my take on this anyway.
Mike




----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Sunday, December 05, 2004 8:10 PM
Subject: Re: Color Fades in discharges


> Original poster: FIFTYGUY@xxxxxxx
>
>     Interesting stuff, Mike!
>     I would think one of the first things to do would be to put gases of 
> known composition into your big discharge tube. Probably start with just 
> pure N2, O2, CO2, Ar, H2O, O3, NOx's, etc, just for control. Then see 
> what happens to a discharge in pure N2 as you add a trace of the others. 
> Maybe by finding out what isn't getting "burnt" will help nail down what is.
>     I think by our minimum BPS for long sparks that there's some 
> time-dependent effect that lasts only a few mS to allow the streamers to 
> extend. A lifetime of a "burnt" product in the air?
>     Might be interesting to also run a Tesla coil discharge through your 
> discharge tube before and after you "burn" the air (and other gases).
>     One wonders if the "burning" is actually due to heating by the arc, 
> ionization of the gas, UV or other radiation, or a chemical reaction with 
> something that IS a direct product of the discharge. Simulating the 
> temperature of an arc without an arc might be tough, but could you 
> illuminate/irradiate gas in the discharge tube first by exposing it to a 
> discharge in a sealed but transparent adjacent chamber? Or could you 
> introduce pure O3 and/or NOx's into the chamber until the air behaves "burned"?
>     Whatabout doing your burning in short bursts, to minimize the 
> long-term heating effects? Is it still the same cumulative time to burn a 
> mixture as it takes to burn it all at once?
>     Seems like an easy thing for us hobbyists to experiment with, as the 
> color change is permanent, visible anywhere near standard conditions, and 
> is apparent in ordinary air. Heck, it's not even dependent on RF, AC, or 
> DC! Unfortunately, it may be pretty important to exclude trace contaminants.
>     Obviously, plasma globes don't "burn" their contents in a few 
> minutes. Fluorescent, neon, and HID lights also last a while (although 
> metal-halide lights do undergo a major color change early and late in 
> their lives, and this probably due to a completely different effect?). 
> Gas tubes don't wear out that quick, do they? Thyratrons and such last 
> for a while, at least. So what's different about air and these gases? 
> Doesn't oxygen "poison" plasma globes effectively?
>     This sounds neato. I'll play with this a bit and report back...
>
> -Phil LaBudde