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Re: 1st notch qnch--update

Subject:  Re: 1st notch qnch--update
  Date:   Thu, 17 Apr 1997 22:52:30 -0400 (EDT)
  From:   FutureT-at-aol-dot-com
    To:   tesla-at-pupman-dot-com


 John,
 
> This is very interesting work!! The changes in quenching during ground
> hits are especially interesting, since you are measuring these with the
> coil running at relatively high rep rates. 
 
> When I did my experiments, they were "single shot", using a storage
> scope and firing at a rate of perhaps 2-3 times/second. I slowly
> decreased the distance between the toroid and the grounded electrode
> until I could capture the effects of a "single shot" discharge to
> ground. Under these conditions, the toroid voltage was very near its
> peak value, and the resulting discharge removed virtually all of the
> secondary energy (and indeed all of the remaining "bang" energy) in 1-2
> microseconds. Since there was no energy left in the secondary:toroid,
> there was none left to reflect back to the primary and quenching
> consistently occurred AT the first notch. I had previously thought that
> if the discharge occured earlier in the transfer, the primary energy
> would continue to get dumped into the secondary... your experiments seem
> to indicate that this clearly is not the case. After thinking about it
> some more, the reason is becoming somewhat clearer.
 

> Some speculation:
> Once you've heavily ionized the area surrounding the toroid by running
> at higher rep rates, a streamer may "connect" as a ground hit at a
> secondary voltage substantially lower than the peak. If energy is still
> being transferred from the primary to the secondary when this occurs,
> the circmustances are significantly different than the single shot,
> near-peak ground hit. Under these conditions, there's a sudden change in
> termination from the relatively high streamer impedance (the
>secondary:toroid still has relatively high Q), to a relatively low
> impedance, (and low Q) ground arc. As soon as we get the ground hit, the
> much lower impedance, high-current arc causes the secondary Q to drop
>dramatically - so much so that during this surge, the secondary:toroid
> no longer behaves like a series LC resonant at Fo. The transmission-line
> characteristics and surge impedance characteristics of the secondary now
> take over, and because of the large mismatch between the coil Zo and the
> ground arc, we no longer efficiently couple energy to the secondary. The
> residual energy in the primary's electromagnetic field now couples back
> mainly into the primary, and the secondary arc is extinguished. The
> second (but significantly lower) hump occurs as the energy transfer
> process resumes, and quenching now occurs at the second notch.
 
> Make sense? Any other thoughts??
 
> Safe coilin' to you!
 
> -- Bert --
  >>

Bert,

An excellent analysis!  I hadn't considered the timing of the ground
strikes,
but your explanation makes perfect sense, and explains both our
(opposite)
results.  The part about the ground strike shorting the coil output
agrees
with Malcolm's suggestion that the secondary acts like a shorted-output
quarter wave transformer and results in the primary "looking" at a high
impedance.  Guess we can't escape radio theory.

As you said or implied (plus I threw in a couple of my viewpoints here,
which
you may have mentioned in the past also), in many cases, the streamers
from a
previous gap firing which failed to hit a ground (but came close) may
leave
behind an ionized trail which then on the next gap firing easily (and at
a
voltage below the peak), re-ionizes the trail and connects with ground. 
Once
the streamer hits ground, subsequent streamers probably require
relatively
little voltage to hit ground again and again, as long as the ground
strike
lasts.  Probably, at times, the initial ground strike occurs at the
peak, in
which case quench would occur at the first notch, but it would be
impossible
to see this on the scope (due to human limitations) since all that would
be
noticed (on the scope) would be the subsequent lower voltage ground
strikes
which would cause second notch quenching.

All in all Bert, there's not really much I can add to your concise and
thorough posting.

Towards optimal coiling,

John Freau