Re: the cure for racing sparks

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

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Bert Hickman wrote:

> backfiguring the estimated RC for this system implies an arc
> resistance in the range of 5000 - 10000 ohms. 

That sounds like a more realistic value.  If the value happens to
be higher than the secondary resonator's characteristic impedance,
(32Kohms for Thor) then the system retains the odd-wave mode 
spectrum of the unloaded coil, albeit with the frequencies shifted
somewhat and the Q factors reduced.  We may expect to see a 
qualitative change in the behaviour of the system when the
discharge resistance crosses the characteristic value.

Some work is needed on the modeling software.  The heuristics
currently used to hunt down the singular values of the determinant
in equation 6.10 of http://www.abelian.demon.co.uk/tssp/pn1401.html
work fine when the load resistance is either well above or well
below the characteristic impedance.  But they fail miserably for
the heavily loaded cases in between.  Not a fundamental problem -
just a different approach is needed.  As soon as this is sorted
I'll make up a web page of transient responses, perhaps as a
function of normalised load resistance.

> I also agree with your comments regarding influence of topload
> coupling to the upper portion of the winding.

Yes, and perhaps also the close proximity of the toroid allows eddy
currents in the shorted turn to dampen the HF modes.  The effect of
the shorted loop at the operating frequency is quite small, 
because the loop resistance of the toroid, when reflected to the
secondary, is quite small compared with the ESR of the coil. Ditto
the reflected reactance of the toroid loop.  But at higher
frequencies we might expect more of an effect.

> The "racing sparks" nut is beginning to crack... :^)

We've got quite a collection of possible explanations and we now
need to test them against some real coil measurements. I suppose
racing arcs will never be eliminated because folk will just wind
up those variacs until the problem reappears again in some form or
another.  I guess the best we can hope for is to push back the
limits a little here, a little there, by understanding the various
mechanisms better.
--
Paul Nicholson
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