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>

Marc wrote:
> the coupling magnetic field from primary to secondary forms may
> be a very efficient transfer, When the secondary tries to
> reverse this charge, There is simply far too little windings!

Antonio wrote:
> the coupling coefficient measured in both directions is exactly
> the same

Marc, 
Antonio is of course correct, and I seem to remember giving a
similar answer when you asked me about this some time ago.

But I've since wondered about some possibilities that may arise.
For example, if heavy streamer loading or a solid discharge arc
is present on the topload, this alters the tuning of the resonator
and is likely to trap some energy in the secondary.  For example,

#8 Discharges to earth from the topload redistributes the coil's
   remaining stored energy into a 1/2 wave mode with a volts max
   around a third to half height. (RV) Cure: stay with streamers
   to air, or use wider toroid.

Consider a coil tuned Fpri=Fsec. Half a beat after firing, the
firing energy has transferred 100% to the secondary, and the
topload begins an arc discharge to a grounded point, say.  Both
ends of the coil are now clamped to earth potential and most of the
remaining stored energy in the secondary takes up a half wave mode.
This continues to resonate, but at a frequency more than twice as 
high as the coil's original Fsec.  Thus the symmetry of the 
dual-resonator is thoroughly broken, the energy can't transfer back
very well at all, and the secondary must withstand this condition
until the energy dissipates in the arc.  So here is a case where
Marc may have a point.

It's also notable that when modeling resonators in various states
of offset tuning, there is no great tendency to produce higher than
normal voltages.  As tuning is adjusted either way, the voltages
and currents in the secondary come down from their in-tune values.

We can see this in Terry's very nice animation, 

 http://hot-streamer-dot-com/temp/Animation4.gif

in which we see the coils response becoming lower in amplitude as
(presumably) the primary tap is moved out a turn at a time. We just
don't seem to see any significant increases in voltages anywhere
when the primary tuning is offset or the coupling is raised. With
offset tuning mostly what happens is the secondary V and I goes
down, and a lot of the primary energy remains in the primary to
harmlessly dissipate.  When the coupling is raised, V and I go up
a little because there's less loss, the energy transfers quicker,
but that's about all.  All we can conclude from this observation 
is that lacking a mechanism in the linear (below breakout) regime
of the system capable of explaining the apparent sensitivity of
racings arcs to coupling and tuning, it does seem that we have to
look at the effect of streamers and discharges on the coil in order
to find viable explanations.

Discharges certainly, and streamers probably, have the ability to
drastically alter the configuration of the resonator on-the-fly,
so to speak.  What started out as an in-tune resonator may be 
behaving quite differently half a beat after firing.

We so often hear cases of racing arcs being cured by a slight
alteration of tuning - more C or more L on the primary. Perhaps
this is just that detuning away from Fpri=Fsec is curing the
racing arcs simply by reducing the secondary voltages?  But that
probably isn't the whole story, and I'm keen to take a much closer
look at how the secondary reacts to the loading we demand of it.

Terry wrote:
> However, your animation shows just such an effect!!  The only
> thing wrong with the coil was the tuning ws off, (it was very
> sharp).  Once the coil was in tune, it ran perfectly.  The coil
> never showed signs of racing arcs.

That cuts right to the heart of the matter. The thing I want to
know is why is the tuning so sharp.  Is the real 'best' tuning
some compromise between ability to deliver discharges in the first
place, and the coils ability to withstand their backlash, so to 
speak?  My approach to this is to examine the tuning of coils that
have been set up to what their operators consider best performance.
This is the idea behind the page
 http://www.abelian.demon.co.uk/tssp/cmod/
and I think there's lots to be learned this way without requiring
much fancy instrumentation.

Marc wrote:
> ...several renowned coiling theorists

Ah, so much nonsense has been written up by renowned coiling
theorists. We have to tread very carefully in order to sort things
out.  And I find it pays to take note of what experienced coilers
are saying about how their coils behave, even if it doesn't make
sense by available theories.  It usually means there's something
interesting to uncover - some new understanding just around the
corner. 

And Boris's potato, refering to a secondary voltage profile
occuring when Fpri >> Fsec, I think this is an example of 

#4 Gross tuning error: (RV) Primary is exciting 3/4 wave mode to 
   produce a voltage max around half height. Cure: sort out the
   primary tuning error or cap fault.

and we're beginning to see the 3/4 wave appearing, giving a lift
to the lower part of the profile.  This is taken to its extreme
when the primary is tuned up to that mode, as in 
 http://www.abelian.demon.co.uk/tssp/pn040502/tfsm1-hf.anim.gif

BTW,
Terry's animation demonstrates that although we casually talk about
the secondary 1/4 wave mode 'splitting' to form the double hump,
it isn't really splitting - instead the primary resonator has
brought an extra resonance with it.
--
Paul Nicholson,
Manchester, UK.
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