Re: 1st notch qnch--update

Subject:  Re: 1st notch qnch--update
    ate:  Wed, 16 Apr 1997 10:10:08 -0700
   From:  Bert Hickman <bert.hickman-at-aquila-dot-com>
Organization: toneridge Engineering
         To: Tesla List <tesla-at-pupman-dot-com>

> All,
> In todays tests, I first tightened the coupling, then went >back and re-checked the quench at lower power.
> At k = .11, I had been obtaining 1st notch quench at 2640VA.  >iightening to about k = .13, still obtained 1st notch quench.  >ightened further to about k=.16, but the quench moved to the >econd notch, and racing sparks destroyed the secondary by >burning through in two places.  Small incremental
>changes in sec. height were unable to bring about 1st notch >quenching at these tighter couplings.  Quality of quench >seemsextremely dependent on >ightness of k
> value, magic k values seem to provide a small benefit in >quenching.
> Good
> tuning is is a prerequisite for good quenching.  By changing the tune
> point
> by one turn, the quench moved from the 1st notch to the 2nd notch and
> stayed
> there when a streamer hit a ground.  With proper tune point, quench
> moves to
> the 2nd notch only when spark hits a ground.
> Next I patched up the secondary and changed the system back to 360VA to
> see
> if the recent sync-gap modification would improve the quench at low
> power.
>  Originally, the electrodes were less than 1/8" in dia, now they are
> over
> 1/8" in dia.  The quench has now improved from the 2nd notch to the 1st
> notch.  In addition, the gap originally had 12 series gaps, now it has
> 8, but
> the benefit of the wider electrodes has overwhelmed this change.  Wider
> electrodes for better cooling and quenching were recommended by Dr.
> Resonance,  by Bert H. and probably others.  I do not know if using even
> wider electrodes would improve the quench at these power levels, it
> seems
> there would be a point of diminishing returns.  Free ringdown time is
> now
> about 120uS due to the higher frequency which results from this smaller
> (4" x
> 17") toroid.  Basically, I did not see any change in spark length (still
> 37"
> to 39") for 1st notch versus 2nd notch quenching.  I think this is
> because
> even when the gap quenched on the 2nd notch, very very little energy was
> left
> in the second energy packet, so it just didn't make much difference.  I
> lowered the secondary to 5/8" above the primary (about k = .16), still
> quenched (mostly) on 1st notch, and another streamer started to form.
> My
> next test will be to tighten the coupling even more, and see what
> happens.
> After that, I may go to a non-sync system to compare small-cap, high
> break-rate operation with my previous (above) results.  I will be
> looking at
> overall efficiency, and ease of quenching.
> Comments welcomed,
> John Freau


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 --