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Re: spark length vs toroid diameter

Subject:  Re: spark length vs toroid diameter
  Date:   Fri, 9 May 1997 01:47:13 -0400 (EDT)
  From:   richard hull <rhull-at-richmond.infi-dot-net>
    To:   Tesla List <tesla-at-pupman-dot-com>


At 01:17 AM 5/8/97 -0500, you wrote:
>Subject:     Re: spark length vs toroid diameter
>      Date:  Wed, 07 May 1997 18:58:24 -0800
>      From:  Greg Leyh <lod-at-pacbell-dot-net>
>        To:  Tesla List <tesla-at-pupman-dot-com>
>References: 
>           1
>
>
>dw pierson wrote:
>
>>         Assuming the rest of a given coil setup can provide some
>>         arbitrarily high voltage (eg: low enuf losses, high enuf
>>         power), the spark over distance is set, largely, by the
>>         terminal (toroid, sphere, whatever) diameter.  A 'zero radius'
>>         terminal (point) will spark out at a relatively low voltage.
>>         If LOTS of power is available, there may be long sparks.  A
>>         larger toroid will 'allow' higher voltages before sparking over.
>>         (Of course changing toroid size also changes tune, all the
>>         way back thru the system, so simply dropping on a new toroid
>>         to see the effect can be complicated to interpret...)
>
>
>There are several points to consider here:
>
>1)  Why then wouldn't a hemisphere on the top of the coil be the best?
>
>2)  Some coilers report getting longer arcs by putting breakout points
>    on their toroids, which actually compromise the hold-off voltage.
>
>3)  The streamer itself, once formed, acts as a sharp wire hanging off
>    the toroid, further compromising its holdoff voltage.
>
>It would seem that a larger radius of curvature isn't necessarily
>the reason for longer arcs.  What else could it be?
>
>-GL
>
>
Grag,

All good Questions and thoughtful, too.

1.  The hemisphere, provided it had a rolled under lip, would indeed be
the
ideal form of Terminal.  They are not very dimensional stable though
compared to toroids.  I have used hemispheres a lot until I found I
needed
one 60" across and ran headlong in the fabrication issue.  The lower
slowly
rolled under lip is a must have and complex to produce.  Toroids are
rather
easily fashioned by amateur hands.

2.  Ah, but there is a small art involved here.  The "points" are not
points
at all, but artfully crafted rounded flowing perturbances designed to
just
marginally upset the terminal system.  In this manner the spark action
can
be controlled and nearly the max potential of the terminal realized. 
This
art is paracticed by very few folks.  I think We here a the TCBOR first
mentioned it and a number of other class A builders are taking advantage
of
it now.

The idea of usuing an actual point, as in the classic pointed metal rod
dangling over the toroid, is like throwing the toroid on the floor!
(well
almost)

3.  Once the streamer leaves the toroid, the energy is in the bolt.  Its
wad
is shot until next blast from the gap.  If regualr enough and of
sufficient
energy, the spark grows out farther based on the toroidial energy store. 

 I still have no explanation for why the spark grows and grows to say X
distance and then dies quickly only to restart in another direction when
a
nice channel has been opened.  I am sure lots of ad hoc, handwaving
references to a number of ionic gaseous conduction, thermal convection
or
breakdown laws, associated equations, etc might give comfort to those
who
are uneasy and might be demanding to settle the matter quickly.  I would
like an nice answer with good cogent reasoning behind the phenomenon.  I
once thought thermal conditions might be the causitive agent, but now
don't
hold with that as the sole agent. (though still it lingers)

Again, Good questions.

Richard Hull, TCBOR