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Re: Optimal Quenching Tests

In a message dated 97-01-03 05:17:28 EST, you write:
<<  
 >> Hi all,
>> snip      
> >       I'm presently exploring the benefits of quenching the spark-gap arc
at
 >> the first RF beat frequency "notch" (1st beat notch) in the tank energy.
 
> snip
 
 >>Anyway, we need a better spark-gap design
> > (or a replacement for the spark-gap) to test the benefits of fast
quenching
 >> at high power levels  Has anyone done any work along these lines?
 Comments
 >> or suggestions anyone?
 >> John Freau
 
 
> John,
 
>My work over Christmas shows severe attentuation of the RF envelope with 
 >proper quench. (you get a beautiful ring wave though)  It was only with a 
> long primary/secondary interaction time (5-15us for 500 khz coil) that 
>sparks grew to max length.  You'll see this in tape #55 which will be in 
> the mail to you in the next day or two.  Obviously if we leave the spark 
> on to long for a given coupling, we have a bad situation.  It is 
> important to realize that max spark is what we, as Tesla coil buffs, are 
 >after and not necessarily good tune or quench which would satisfy theory 
> or a bunch of radio engineers.
 
 >I'm still workin on this along with the electrostatic part of TC output.
 
 >Richard Hull, TCBOR
  >>

Richard,   All,

I've been reviewing some of my notes:

1)  I incorrectly posted that my 550 kHz , k = .09, TC quenched optimally
(for best spark), at 4 uS,  quench for best spark was actually at about 8 uS.
 It was a  k = .22 test that gave best spark at quench time of around 4 uS.

2)  There seems to be differing definitions of the theory of optimal
quenching:    It is my understanding, based on the work of the Corums, that
the optimal time to quench is at the first beat frequency notch, which
results from the split frequencies created by over-coupling.  This notch does
not occur until a certain amount of beating takes place, the exact amount is
determined by the degree of coupling.  I did the calculations, for the above
(k = .09) TC, and the optimal quench comes out to be very close to the figure
of 8 uS:    The Corums' theory states that (for the low loss case), the
optimal spark duration is approximately equal to:   1, divided by twice the
difference between the high and low spectral components.    In the above TC,
there's a spectral split of about 50 kHz.  50 kHz times 2 = 100,000, and 1
divided by 100,000 = 10 uS,  losses will tend to shorten the required quench
time, thus there is good agreement with the 8 uS quench time I obtained.  I
see no conflict between my (or your) results, and the Corum's theory of
optimum quench times.

3) It seems to me that as the RF energy in the primary plunges downward
toward the first beat freq. notch, the energy concurrently builds in the
secondary.  When the energy in the primary is at a minimum, and has been
transfered to the secondary, which is now at a maximum,  that is the time to
quench.  If the spark is quenched after only 1 RF cycle, at this low value of
k, the energy will not yet be fully transfered to the secondary and spark
output will be poor, as you found in your thyratron experiments.

4) Quenching too soon is not something that any coiler builder using a spark
gap has to worry about.  It is almost impossible to quench even at the first
beat frequency notch, (8 uS in the above case),  Richard's thryratron system
is probably one of the few quenching methods that is capable of quenching
BEFORE the first beat-freq-notch.

5) My results seem to indicate that spark output falls off rapidly as quench
time moves outwards to the 2 nd or 3 rd beat freq. notch.  The 2 nd notch
corresponds to  approximately the 17 th RF cycle of ringdown.  The 3 rd beat
freq. notch corresponds to approximately the 28 the RF cycle of ringdown, in
above TC example.  Most TCs  quench somewhere between the 3 rd, and the 6 th,
beat freq. notch--and that's with good quenching.  Who knows where poor
quenching TCs quench?   

6)  When I quenched at 8 us in the above example,  I saw no notches in the
secondary waveform;  I saw only a build-up, followed by a nice high amplitude
ring-down.  But yes, I agree, more work needs to be done to verify the
 optimal quenching conditions needed for optimal spark output.

Happy coiling!

   John Freau