Re: More on spark delay

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Hi Ken,

The breakdown sequence of Avalanches --> Streamers --> Leaders will
preferentially "originate" from  points which are under the highest
E-field stress. Terry's E-Tesla6 program can, in fact, be used to help
predict the location of these regions. For a typical Tesla Coil with a
relatively flat primary and a toroidal topload, the regions with highest
E-fields tend to be along the outer surfaces of the toroid, explaining
why toroids help shield the secondary and help throw sparks outward and
away from the primary. The region near the flat primary plane tends to
be at a much lower E-field stress, so breakout normally does not tend to
originate there. BTW, this electrode configuration directly corresponds
to the definition of a "nonuniform gap" in my previous posts. 

Now suppose you altered the primary's geometry by creating a sharp point
poking upwards from the plane of the primary. Under the right
conditions, you will see streamers heading upwards from this point,
particularly when the coil's output voltage is not quite sufficient to
cause breakout from the toroid. I accidentally had this happen on one of
my coils when I tapped the primary from the top side - short (6-8")
streamers were observed heading upwards from the primary tap towards the
upper region of the secondary, connecting every now and then to the
secondary. 

Suppose you move a grounded wire towards a toroid in a system that's
operating just below breakout. In this case streamers and short leaders
will be seen "originating" from the wire, heading towards the toroid.
The grounded wire has now become the more highly stressed electrode in a
nonuniform gap, and streamers now originate from the wire instead of the
toroid. 

BTW, a similar thing happens in nature during negative Cloud-Ground
lightning: a descending negative leader reduces its distance to the
ground, increasing the E-field in the region between itself and ground.
As the leader approaches ground, points of locally higher E-field stress
on the ground will now begin to originate upwardly directed positive
leaders. When one of these upward leaders "connects" with the downward
leader, the full lightning discharge occurs. Upward directed "arrested
leaders" can still carry substantial current (tens or even hundreds of
amps). So, even though they may never actually "connect" to the
cloud-based leader, they can still can cause significant damage to
electrical equipment and injury/death to those in the current path.

Best regards,

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Coins Shrunk Electromagnetically!
http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Kchdlh-at-aol-dot-com>
> 
> Bert (& all)-
> 
> Apropos the following--in a typical Tesla coil system, can you say what the
> significance is of the (apparent) facts that a) sparks emanate from the
toroid
> exclusively, absent a near-enough grounded surface or point, and never, say,
> from the apparatus of the primary (which is essentially at ground) or from
> points on the ground-surface itself beneath the coil apparatus; and b) even
> with surrounding grounded surfaces and/or points present, they being far
enough
> away so as not to seem to emit sparks, the sparks still appear to come "from"
> the toroid?
> 
> I realize that, in the dark, one can see leaders (if that's the proper term)
> apapearing at this object and that--but the big, apparent spark always jumps
> off the toroid.
> 
> Ken Herrick
> 
<SNIP>