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RE: TC Limits

Hi Mark,
For long sparks higher charge frequencies result in higher losses so lower
charge frequency coils prevail.
Your need for only 50kV may mitigate what most are after - long sparks.
There are small ones, such as my furnace igniter about 1.5" tall !
even stun guns use the TD technique (spark gap and all)

The coefficient of coupling is easiest set empirically, 
increase Pri/Sec proximity until onset of undesirable 
arcing Pri to Sec or inter Sec then back off a bit.

I've experimented with standard Xenon flashtube gaps 
on my .1uF 7kV 2.5J manually triggered DCTC (see archives)
Tubes long enough to hold off sufficient voltage possess too much series R
My TC did fire but at much sacrifice of spark length.
If you parallel enough long ones it may work well enough.
I was using 4-6"L 1/4 to 3/8"D tubes which were designed for 
~2kVdc (20uF = 40J) fire with hold off ~5kVdc (too low for most TCers)

Tubes short enough to be low series R possess too little hold off voltage.

If one could custom the tubes a good compromise could likely be reached.

My manual pneumatic control implements Jennings or Kilovac 25kV vacuum SPDT
relay 
jogging the contacts close enough to arc w/o closing to avoid welding.

Regards, Dale
Redondo Beach, Calif

-----Original Message-----
From: Tesla List [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, March 22, 2000 6:30 AM
To: tesla-at-pupman-dot-com
Subject: TC Limits


Original Poster: "Mark Fergerson" <mfergerson1-at-home-dot-com> 

  Greetings all, newbie ex-lurker (1 whole week) here!

  Some time ago I posted a request for some TC info on
sci.physics.electromag and was referred here (thanks Dan Kline). I've
been all over the Tesla Ring, and still have some questions.

  A lot of posts about record (large) TC's here of late. Anybody ever
think about record _small_ ones? I'm envisioning a bipolar model;
helical primary 2" long, 4" dia, secondary about 10" long, 2" dia,
running at 1 MHz. It isn't intended for spark generation, but rather
to power a small particle accelerator in pulse mode (I may not even
want a TC; that's why I'm here). The electrodes (rings spaced
exponentially) are the "topload" of around 75pF. I'm looking for about
50KV. I plug the numbers into several TC design programs and I get
reasonable numbers for wire size, number of turns, supply voltage,
etc.

  I picked those proportions from memory of a photo, BTW.

  What are the length/diameter ratio limits for a "good" TC? Why do
some folks think a secondary 2"dx10"l is fine, others say it's less
than ideal? What is ideal, anyway?
I've heard a lot of opinion, but little justification.

  As extreme cases, I can see that a very long secondary would have
too many windings out of the influence of a very short primary to be
worth the trouble to wind, and a secondary the same length as the
primary would would be prone to interwinding arcover, but where's the
breakpoint? What constitutes "long" and "short" here?

  What are the operating frequency limits, and why? I was told a TC
couldn't operate satisfactorily at 1 MHz. Why won't they scale?

  How do you estimate coefficient of coupling for a particular
geometry (preferably without using calculus)? <math pun>

  Anybody think a standard Xenon flashtube (or rather several in
series/parallel) with some kind of magnetic quenching arrangement
would do as a "spark gap" in a low-power design? They're designed to
switch currents quickly at fairly high voltages, their electrodes are
fairly erosion-resistant, and they can be triggered reliably.

TIA

  Mark L. Fergerson