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Re: [TCML] Extrodinarily Rudimentary Question From Newbiest Naif

Hi---
Jim Lux's explanation is good. The potential (voltage) of the toroid of a TC is a few hundred thousand volts, so the atmospheric potential gradient of 100 volts per meter or so has little influence. Sparks don't jump to a potential, they jump to a charge, directed by the potential gradient.
When the toroid is negative, it has an excess of electrons which are all pushing against each other. This repulsion is what we see as voltage, and the gradient of this voltage is directed outward. When the voltage becomes sufficiently high, electrons break free of the toroid and form a channel traveling outward from the toroid, following the voltage gradient (usually called the potential gradient). The channel (called a leader) propagates because the electrons at the tip are pushed forward by the ones behind them. As the leader travels, electrons are stored in the air around it, and when the toroid voltage drops to zero there is little impetus for the leader to go further. It then goes out, but leaves behind a cloud of electrons where it traveled. The path of the leader is heated from its passage, and so remains conducting for many microseconds. During the next half-cycle the the toroid voltage becomes positive, and the same process happens, but this time the leader propagates along the heated path by pulling electrons back into the toroid. This is a little harder to visualize than the negative case. This process is exactly the same as lightning propagation, except that lightning is not oscillatory.
The leader lights up because the potential gradient at the tip of the spark is very high and removes electrons from some of the atoms it encounters, leaving them ionized. When the atoms reacquire their electrons, they emit light at frequencies determined by the type of atom.
The currents in a propagating lightning leader are of the order of several hundred amps. When the leader contacts the earth, a current of 20,000 amps or so travels in the channel which has been prepared. This is the dazzling spark we see in cloud-to-ground lightning. When we see "spider lightning" in the clouds, we are seeing the propagating leaders without the high-current flash. When the TC spark contacts a grounded conductor, we get a similar much brighter spark along the leader path. It would be fun and interesting to measure the currents in these two types of TC discharges. But not easy. My MicroCap circuit simulator says that the current in the propagating leaders should be about a half amp, but there are many aspects of reality that can't be put into a simulator. The average current in the discharge is much lower due to the pulsed nature, but the half-amp explains why them suckers hurt so much.
An excellent reference for lightning information of all types is "The Lightning Discharge," by Martin A. Uman. Every TC dude who is even half-serious should have this book. Earlier editions were published under the name "Lightning." Good explanations of the atmospheric electric field and all aspects of lightning are given.
There are many amazing videos of lightning leaders on Youtube taken by Tom Warner. Check this one out and follow the links for many others. Astonishing stuff. 

     http://www.youtube.com/watch?v=A0XkNfTyR9A

You can also check out his website at ztresearch.com.

---Carl






Hi Jim and thanks for responding.

Its interesting you mentioning lightning because atmospheric
electricity is closer to my knowledge base than artificially produced
currents. I have been researching static fields, both environmentally
and artificially produced and I wrote because coming from a geophysics
point of view, the arc would appear to be arcing to the atmosphere
itself.

I wanted to ask this question to see if there were a consensus among
Tesla experts and if there wasn't, I wanted to propose a simple
experiment which should to illustrate the actual dynamics of a "sky
arc".

A Not sure how tight you are with geophysics but bear with me if its elementary.

What we call atmospheric electricity is also known as the potential
earth gradient (PEG). PEG is the potential electric field difference
which exists between the surface of the earth and the ionosphere. For
every foot nearly a hundred volts on average. During an approaching
storm it can be in the thousands.

To find out whether a Tesla coil is indeed arcing to the atmospheric
potential one could count the number of sky arcs over a given time,
then do the test again when then the atmospheric potential has been
altered. If the coil is arcing to the atmospheric potential then the
number of arcs would vary accordingly.

Fortunately, nature has made it quite simple since the field naturally
varies during the course of a day. These fluctuations could be taken
advantage of for this test. Finding these fluctuations can be made
quite simple with a fiber glass fishing rod and s couple pith balls.
Depending on the season and the weather, it would be quite easy to
observe the pith balls diverge to their furthest or closest and then
fire up the coil accordingly.

That is pretty much the experiment I have been planning to set up but
I don't have access to a coil.


One During a storm it can be in the thousands of volts. Over the
course of the day it fluctuates slightly. Over a year and through each
season it also fluctuates slightly.



  I asked because it made sense to me that the arc was arcing to the
potential gradient itself. It would be interesting to conduct some
outdoor tests to determine the number of sky arcs at different
potentials. Over the course of a day, the potential fluctuates, so if
one were to count the number of arcs during these fluctuations we
would know for certain whether a Tesla coil is actually arcing to the
earth potential gradient or not. SBecause of My research has been with
static fields in the isolation of pure thrust

On Sun, Apr 10, 2011 at 2:03 PM, Jim Lux<jimlux@xxxxxxxxxxxxx>  wrote:

On 4/10/11 8:29 AM, nickobert testein wrote:

Hello,

My name is Nick. Just starting to get my head around your concepts. I
just like reading your discussions right now but if its okay with
someone on training wheels with a question. I won't do this often
because its obnoxious walking when you'd rather run but here it is:
when a Tesla coil arcs in the air and not to ground, what exactly is
the arc arcing to?


Not a silly question at all..and one that doesn't have a "good" answer, as
well.

it's arcing to nowhere in particular.  You've got a buildup of charge, that
results in an increase in voltage, the electric field near the topload
exceeds the breakdown strength of air (3MV/meter) and a spark (aka leader)
starts.  current flows into that spark as it grows.. That means charge is
moving off the topload into the spark.
Meanwhile since a spark has some resistance, the current flowing dissipates
heat, so the energy goes into making the air hot (and glowing!)..  The spark
keeps growing, as long as there's charge to keep "filling" the ionized
channel.

However, eventually, the charge runs out, and the spark cools off, and it's
all over, without the spark ever getting to somewhere.

If you look at how lightning propagates, it's exactly the same (on a
somewhat larger scale)


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