Re: More on spark delay

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Kchdlh-at-aol-dot-com>

Peter (& all)-

Comments interspersed...

I

>
> Original poster: "Peter Lawrence by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <Peter.Lawrence-at-Sun-dot-com>
>
> Ken,
>     thanks for the clarifications.
>     
> I'ld REALLY like to match up your SSTC with a streak-photograph of the spark
> formation!!! (I've got the machine shop to make the streak-camera (and I've
> built a turbine engine, so high RPMs are not an issue), but..., my girlfriend
> just moved in and there are so many boxes around the house and shop that I
> can't even get to anything right now... :-)))



Nowadays, I'd think an easier way to gauge the spark's progress might be with a
string of fiber-optic cable-ends placed near the spark path.  Collimate each
one so that its field of view is restricted horizontally.  At the other ends of
the cables, use PIN (?) diodes or the like to generate signals that can then be
displayed on a sync'ed scope.  Display at the same time the toriod's voltage
envelope--and there you have it.



>
> I can only wonder and speculate about whats happening during those:
>
> 32 cycles ring up




Just like that of gap-type coils but slower, of course.  EM radiation from the
secondary components occurs during this time; inefficiently, but that's when it
happens.  If I reduce my primary supply-voltage so that the spark just does not
break out, all the miscellaneous fluorescent tubes, neon tubes, etc. in my shop
merrily blink away during my 5 ms. "on" time; whereas with break-out at 200 us
or so, that doesn't happen.  Once the spark starts, that's where the power
goes.  I'm sure I'm stating the obvious...

>
> 1 cycle break out (people say feeder sparks grow in nano-seconds, not 7us)




No doubt they do.  I sync my scope to the beginning of each ring-up time, so
there's some jitter by the time of break-out, from one spark to the next. 
Thus, I don't have a rock-solid view of the sudden Vpk drop.  What I see is
that a certain negative 1/2 cycle retains the exponentially-increasing slope
and the next one exhibits the 30% drop.

>
> 15 cycle ring down




It's clear to me that this is the time interval during which the Q of the
circuit is decreasing.  At the beginning of it, at least, the Q remains high
enough so that the power being taken from the primary can operate to continue
to raise the toroid voltage.  Much more so in a spark-gap system since that
type of system's power is concentrated into the first few cycles of the
exponentially-decaying excitation.  In my system, excitation remains
substantially constant, but relatively low, during the entire spark event.

>
> 700 cycle steady ringing




The spark gets fatter and bushier.



>
> ? how much energy is built up in 32 cycles, and how much expended in that
>   first 30% drop in Vp-p




As an indicator of this, I note that the envelope-shape of the secondary's
return-current is exactly that of the toroid's voltage.  I also note that the
mains-current going into my system is much greater when I have reduced the
voltage so that sparks just do not break out.  As soon as sparks break out, the
input current drops substantially.  And that is with the same duration of
excitation in both cases.  My MOSFET-excited primary is quite efficient
compared to a spark-gap, so essentially all that power is going into the
secondary system.

This seems to tell me that most of the input energy is going into EM radiation
with not much of it actually going into the spark itself.  Once the Q fizzles
out, it seems there's not as much energy transfer.

If I'm wrong, somebody stop me!


>
> ? how far does the spark grow in that first (nano seconds) break out, during
>   the 15 cycle ring down, during the 700 cycle steady ringing



Yes, that's the big question.  No doubt spark experts can and have answered it;
I haven't checked that out.  It surely depends on the "push" behind the spark,
differing markedly in SSTC vs. SGTC systems.  See my comment above re a
fiber-optic scheme.


>
>   
> ? how much corona develops around the spark during the 15 cycle ring down,
>   during the 700 cycle steady ringing
>
> ? how much brighter does the spark get during...



Questions, questions...



>
> ? what happens after the 748 cycles, do you stop feeding input or does the
>   spark extinquish by itself (if so why)



I stop the input.


>
> ? what would happen if you pumped your TC for only 33 cycles, for 33+15
> cycles,
>   for 48+... cycles



See my posting of yesterday to John Freau & all.



>
> ? is the SSTC different from SGTC because of long ring up time, if so can we
>   simulate this with a SGTC with a really low K coupling value (one could do
>   this experiment with a SGTC by raising the secondary a bunch of inches -
> but
>   then will gap losses start to eat up so much energy that comparisons are
>   meaningless?) 



I think there'd be a problem due to the rapid decay of the primary's power
after the gap fires.  In comparison, my system just keeps pumping away until
shut off.


>
>    
> ? 
>
> so many questions, so little time...!!!
>
> -Peter Lawrence.
>
>
> (ps,
> A comment about the notion of inertial confinement, the air heats up as
> a consequence of the current flowing through it, this lowers its
> resistance and a higher current brighter spark forms. But from basic 
> physics the _expansion_ of the air/plasma actually _cools_ it. I'm not
> saying that inertial confinement cannot be having an effect, I just don't
> myself see how it would. The lowering of resistance of the air is not a
> function of it expanding, at least as I see it. Perhaps high pressure plasma
> does have a high resistance compared to 1-Atm, I don't really know, but I
> always presumed that plasma already had disassociated electrons and thus
> low resistance regardless of pressure...?
> )
>
>
>
>
> >
> >
> >Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <Kchdlh-at-aol-dot-com>
> >
> >Peter (& all)-
> >
> >Comments interspersed...
> >
> >[snipped]
> >
> >
> >>
> >> Original poster: "Peter Lawrence by way of Terry Fritz
> <twftesla-at-qwest-dot-net>"
> >> <Peter.Lawrence-at-Sun-dot-com>
> >>
> >> Ken,
> >>     certainly some of the more interesting observations to surface
> recently
> >>
> >> first lets see if we have the time-base correct:
> >>
> >> 140KHz -> 7.1us AC cycle time.  100us = 14 cycles.  5ms = 704 cycles.
> >>
> >> your wording below leaves me totally confused, can you fill in a simple
> >> time line with voltages:
> >>
> >> cycle voltage
> >> ----- -------
> >> 0     100%
> >> 1     70%  (aka a "30% drop")
> >> 2
> >> 3
> >> ...
> >> 14    ??? stable value ???
> >
> >
> >
> >
> >Right--  I'll try to be clearer this time:
> >
> >1.  Rise to breakout voltage (Vp-p), ~230 microseconds =~ 32 cycles of
> >exact-secondary-Fr excitation.  Breakout is from a polished 6" x 24"
> Landergren
> >toroid.
> >
> >2.  Toroid-voltage drop from -Vpk to ~-0.7Vpk in 1 cycle, i.e., from 1
> negative
> >1/2-cycle to the next.  Sometimes accompanied by a rise of the next +Vpk to
> >~+1.14Vpk (And I don't seem to see that for every spark.  Also, it might
> be the
> >preceding  +1/2 cycle rather than the following one: can't be sure.). 
> Voltage
> >measured via a nearby scope probe--and I suppose it may not strictly be
> "toroid
> >voltage" but rather, may have a "coil voltage" component.
> >
> >3.  Decline from Vp-p to ~0.17Vp-p over ~100 us =~ 14 cycles.
> >
> >4.  Continuation at ~0.17Vp-p for the ~5 milliseconds duration of the
> >pulse-burst.
> >
> >Repeating my hypothesis:  1.  Given sufficient dV/dt, the toroid voltage
> will
> >increase, above what it would be otherwise, during (at least, the first part
> >of) the ~100 us time period, thus producing a longer spark.  And 2.  The
> ~100
> >us time period is caused by the necessity to heat the air and push it out of
> >the way (so to speak).
> >
> >It may be mostly the heating, because of this:  In the past, I had
> contrived to
> >incorporate a mode of operation in which I gated my ~5 ms pulse-burst on &
> >off.  Sixty-four cycles on, 64 off, etc.  That was just for the hell of it
> and
> >I have quit that, at least temporarily, because I had a rash of MOSFET
> failures
> >that I--probably mistakenly--attributed to that mode of operation.  But I
> >noticed that the ~0.17Vp-p level did not change from one 64-cycle "on"
> event to
> >the next one.  And further, I could clearly hear the "musical note" that was
> >created by that on & off characteristic during the ~5 ms follow-on time
> >period.  That would imply that the air, "pushed out of the way" during each
> >64-cycle "on" period, rushed back again--at least, in part--during each
> >subsequent "off" period.  But it stayed hot, with the interrupted spark
> >continuing to go along the same path for the full ~5 ms period (as I
> observed),
> >because the ~0.17Vp-p level r! emained essentially constant.
> >
> >More food for thought, I hope...
> >
> >Ken Herrick
> >
> >
> >
>
>