The smoothness of our toroids

• To: tesla-at-pupman-dot-com
• Subject: The smoothness of our toroids
• From: Kennan C Herrick <kcha1-at-juno-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Wed, 22 Dec 1999 17:42:50 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Here's a comparison test I just made that leads me to think aluminum duct
material may not be all that satisfactory:

1.  I placed on the top of my (MOSFET-driven) t.c. a corrugated
aluminum-duct toroid of 5" nominal c.s.d. and about 15" mean diameter,
reasonably well formed & free of irregularities.   With the 'scope
nearby, I observed that it took 250 microseconds for a spark to occur
after initial excitation, with a pk-pk waveform on the screen of 4 cm.

2.  Next, I placed on top of that toroid an aluminum pizza pan having a
very smooth peripheral "bead" of about 1/4" c.s.d.  I observed 150
microseconds for the spark to occur and a pk-pk waveform of 2 1/2 cm. 
All else in the setup stayed the same.

That seems to tell me that the corrugated 5" toroid is only 4/(2.5) = 1.6
times as good as the smooth 1/4" pizza pan in holding off the spark until
the voltage can build up, as compared to what one might hope from the
ratio of the nominal cross-sectional diameters, which is 5/(.25) = 20.  

Am I wrong?
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