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Re: Positive VS negative streamer
Hi John,
At 12:35 AM 10/28/98, you wrote:
>
> All -
>
> Tesla said that the dominant polarity of the TC secondary terminal when
>the Tesla coil is operating is negative. He said this is due to the the
>dampened wave being off center with the negative peaks being greater. The
>dampened wave has other idiosyncrasies. The peaks of this wave do not occur
>at the same time as a sine wave of the same frequency.
>
> Some coilers have made these tests and said the polarity was positive.
>However, when correctly made the tests indicate the polarity is negative.
>You can verify the negative polarity by doing the the test I posted some
>time ago. I believe the dominant streamer and space charge would be
>negative when the secondary terminal is negative.
>
>Apparently it has been found that with a certain voltage impulse wave the
>space charge is positive. But how does this apply to Tesla coils?
>
> Terry - I visited your site and scope pics. I am always amazed that I can
>print pics so easily that were made by someone else's scope. Thank you for
>making my life so pleasant. The pics do show spikes and they are labeled
>negative polarity! How would you match these spikes to any particular
>secondary spark anyway? Are you saying that those random TC extra long
>sparks are all positive?
>
> John Couture
>
>------------------------------------
>
Hi John,
The digital LCD screen on my scope is backlit so the digital pictures come
out very well. I now have a bubble jet printer hooked directly to the
scope so I can get great printouts with just the touch of the hardcopy
button. All I need now is an overstuffed chair and I'll be set! :-)
Let me clarify the pictures a bit. The sphere on the top of the coil has
two current probes built into it. One measures the current from the coil
to the sphere and the other measures the current from the sphere into a
terminal that the arcs shoot out from. In the pictures, the top trace
(Current into sphere) has the polarity reversed due to the fact that I
wired it the shunt backwards (there is some law of nature that says these
things always need to be done twice to get them right :-)). The bottom
trace is the current into the arc and the polarity is correct in that trace
(up is positive). You see in the bottom trace that the current is fairly
sinusoidal but there are sharp spikes in the positive peaks and only a few
small spikes on the negative peaks. This is very typical of the
measurements I have seen (I have seen hundreds of these waveforms but I
only posted this one typical example). It is very apparent that theses
sharp spikes occur much much more frequently in the positive direction
rather in the negative direction. There have been a number of posts
explaining this effect. Apparently, it has to do with ionization energies
and stuff like that which I don't claim to understand well. However, the
effect is well known in a number of areas of science.
It appears that these sparks are sudden small bursts of energy being sent
to a low impedance arc channel. Sort of like little streamer branches
breaking into new areas (perhaps there is a name for such things?). I
think the arc gets started by these little positive micro streamers and
then the full AC current maintains the arc after that. So positive
micro-arcs are much more likely to start streamers than negative
micro-arcs. I think the net effect would be a neutral charge. However,
spark gaps like to fire and quench at none zero voltages which can easily
lever a net positive or negative charge on the system after the firing
cycle. Multigaps are very good at leaving net voltages while rotary and
simple single gaps ring down to close to zero net voltages. I'll leave the
rest of this to you, Richard and the others who know more about this than I.
The picture in question is at:
http://www.peakpeak-dot-com/~terryf/tesla/misc/spikes.jpg
Terry
References: