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>

Antonio wrote:
> The animated gifs appear to be or too large or are confounding
> my browser

I've made up some half-size versions, about 1/3rd the file size.
 http://www.abelian.demon.co.uk/tssp/tmp/thor.anim1-small.gif
 http://www.abelian.demon.co.uk/tssp/tmp/thor.anim2-small.gif

> If a spark discharges the terminal while the energy transfer is
> not complete, the secondary current may continue to feed the arc
> for a long time.

The above example discharges the topload during the +ve peak of
the 3rd RF cycle - at this point energy transfer has almost 
completed.  If instead we discharge at the +ve peak of the first
cycle, we get

 http://www.abelian.demon.co.uk/tssp/tmp/thor.wave2.gif
 http://www.abelian.demon.co.uk/tssp/tmp/thor.anim3-small.gif

With the primary ringing down at 68kHz and the fundamental mode
of the secondary now at 226kHz, there is relatively little 
coupling between the two resonators.  Nevertheless, a current of 1
amp at 68Khz in the primary induces around 4mA in the secondary,
so with the primary still at 200A after 80uS, we still have 800mA
circulating through the topload discharge, surely enough to
maintain the arc.  In addition to this, we still have the currents
due to the secondary modes contributing to the arc current too.

> How is the model?

The Q factors in the simulation are probably unrealistically high,
because I just guessed a very low constant 50 ohms for the
discharge arc resistance.  So the Q factors and the ad hoc
breakout threshold are guesswork but the rest of the model should
be accurate to a percent or so.  The secondary is modeled in 235
steps for these examples, and we're only considering modes below 7
Mhz.

This model is able to compute the response of the system to the
non-linear boundary conditions of the loaded secondary, and the
problem now is determining what those boundary conditions are for
a typical or particular coil breakout.  We need to know Ctop as a
function of either Qtop or Vtop.  Nice but less important would be
to find the effective shunt conductance as a function of Qtop or
Vtop.  Work is ongoing to obtain this information, approaching it
from three angles - precision measurement of topvolts using an oil-
filled capacitive divider;  analysis of base current waveforms
to identify the resonant modes and how they change during the
firing event; and modeling of systems tuned for optimum breakout
performance.  Each of these three approaches should lead to an
estimate of the non-linear load function, so each method has two
independent cross-checks.
--
Paul Nicholson
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