Re: More on spark delay

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Ken,
        Despite my lack of responses to your posts I do read them and 
take an interest in what you are doing.

On 22 Apr 2002, at 17:11, Tesla list wrote:

> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Kchdlh-at-aol-dot-com>
> 
> I've put forth my hypothesis more than once that the relatively high
> rate-of-rise of spark-gap-coil voltage is the reason that spark-gap
sparks are
> longer than SSTC sparks.  I've proposed that that high rate allows the toroid
> voltage to rise higher during the time it takes for the spark to propagate. 
> That time period exists due to the necessity to heat and displace the air
along
> the spark's path.
> 
> The notion has received scant attention.  I may be repeating myself but
here's
> an observation I just made today:   In my SSTC, the toroid voltage's rise &
> fall is extremely stable from spark to spark.  So, I can sync the scope to it
> and accurately gauge the rise and fall.  I find, at commencement of the
spark,
> that the toroid voltage falls abruptly, at first, to about 70% of the level
> that it holds during the remaining 5 milliseconds of the spark's duration. 

Just to be clear; is that 70% of the initial voltage or ?  The drop 
is to be expected of course. A drop of that magnitude suggests that 
50% of the energy in the top capacitance is being dissipated.

> That fall seems to take place well within 1 cycle of the excitation, which is
> at ~140 KHz , and it always occurs at a negative half-cycle (indicating to me
> that the spark initiates when the toroid is 'crowded" with electrons and not
> otherwise).  It then takes just about 100 microseconds longer for the voltage
> to decline further to the steady level.
> 
> Clearly, at the instant of the 30% drop, the impedance of the initial
spark has
> appeared in parallel with the impedance of the capacitance between the toroid
> and ground.  But at the end of that instant, the spark impedance is still
> relatively high since its presence in the series circuit of
> ground/secondary/toroid:ground capacitance/ground (across "toroid:ground
> capacitance") has diminished the toroid voltage by only that 30%.  The spark
> impedance then relatively-slowly decreases during the following 100 us,
causing
> the toroid voltage to correspondingly diminish.

Which supports the observation of prolonged ringing for air streamers 
and a still rather high loaded Q under those conditions. 

> So my supposition remains:  It is the capability of spark-gap systems to
> deliver higher power during the (at least first part of) 100 us or so that
> allows for the longer sparks.  And it is the physical/thermal inertia of the
> air in the path of the spark that causes the 100-us phenomenon to exist.

I've heard the phrase about the abrupt rise of terminal voltage prior 
to breakout as akin to "shocking the air" or something similar. So 
what happens if the system is operated on the edge of breakout? Of 
course, further powerful shocks in the form of subsequent ringups 
would do the lengthening trick alright. Single shot would probably do 
no better than a slow ringup to breakout voltage. Indeed, my largest 
disruptive coil stretches five times further when repetitively fired 
than it appears to do when sshotted. I say "appears" because there is 
a distinct possibility that streamers which would be visible under 
only the darkest conditions streatch out a good deal further. I have 
observed this phenomenon more than once.

Regards,
malcolm

> But perhaps this is old-hat to spark experts.  Comments?...
> 
> Ken Herrick
> 
> 
>