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Re: stepped leaders
Hi Robert, Jim, all,
Just to elaborate on a couple of points....
> I have to tell you, and remind the audience, that you have had a
> distinct advantage over most of the rest of us in your ability to
> actually 'scope' waveforms pertaining to coil operation. I have
> gotten to where I am now mainly, by mental visualization and then
> tuning the design for the biggest arcs.
(see note at the end of this piece)
I strongly recommend anyone who is interested to get hold of a paper
written by Abramyans on a "Tesla Transformer Accelerator". The article
gives the waveforms (I've been seeing) for different values of k, a
graph showing efficiency vs system Q etc. It is VERY heavily
overcoupled at k=0.6 with Q's of 20 or so for both primary and
secondary to give total energy transfer from primary to secondary
in just two "gap conductions" or half cycles of oscillation with few
losses. I'd imagine he is not using a standard air sparkgap in order
to get primary Q that high.
> You said: "From this you can see where the oomph of a magnifier
> comes from - a much higher value of K (greater rate of energy
> transfer) with a consequent reduction in gap conductions and hence
> (increasing?) losses. <snip> I'd suggest that this improvement in
> performance shows just how bad the gap really is."
I basically meant that gap losses were proportional to the number of
gap conductions.
> Are you refering to the fact that with a higher system K, because the
> gap dwell time is reduced, assuming the gap never gets any better per
> unit of time than C as a conductor, shorter dwell means reduced net C?
I'm not quite sure what C refers to. A couple of notes: for every half
cycle of energy transfer, the gap conducts and loses energy in a big
way. The higher k is, the fewer half cycles are involved for the
transfer to go to completion. If the secondary doesn't spark this at
this point, it'll go straight back to the primary and another round
of trading begins with more energy wastage in the gap.
Second note: The gap losses are inversely proportional to any
other losses in the circuit. In other words, if you have a
superconducting primary, lossless cap, no radiation and no secondary
present, all losses are in the gap. If the primary is otherwise
lossy, gap losses become a smaller fraction of the overall loss. For
this purpose, you can count energy "lost" to the secondary from the
primary.
Because of the tiny time difference (fraction of cycle) between
what the primary is doing and consequent takeup of energy by the
secondary (and assuming the secondary is tuned properly), the primary
"thinks" it is coupling to a black hole - well almost. In fact what
proportion of remaining primary energy disappears into the "black
hole" is governed by k (which is a description of what proportion of
primary flux is also linked to the secondary). Hence the impedance
that the primary "sees" is inversely proportional to k (and possibly
to some power of k (npi)). Any reflections from the top end of the
line that are not in the correct phase increase this impedance as
there is less of a "flux difference" between the two.
The inverse of the above is true at the point where all the energy
(minus losses) has ended up in the secondary and is now starting to
work its way back into the primary. A good output arc ensures this
energy transfer is pretty much one-way. If there isn't a good energy
sink from the secondary, it would take humungous efforts to quench the
gap to stop the process reversing because the time between the
secondary being "full" (and primary empty) and the next half cycle
of secondary ring is VERY short compared to the time it would take to
deionize the gap.
> You then conclude: "The multiple beat envelope one gets shows that
> the system is vastly overcoupled before spark production." Yes I
> agree with you, this seems intuitively correct.
>
> DING, light going on! This is the scientific explanation why on a
> sizeable system, when big power is going in, and no streamers are
> yet coming out, the rotary break is beating itself up! (with
> greatly increased light output). I used to give this the casual
> explanation that the input energy was merely 'piling up' at the
> break contacts, but you've just cleared it up for me!
> The much higher K (no streamer condition) DEMANDS that the interplay
> between primary and secondary in the gap last for many more RF cycles,
> than if a streamer is pulling power from the system at the output
> end. In this situation the mechanics of the break are overcome
> and a form of 'power arcing' (extended interplay) is apparently
> innevitable by this explanation.
Agree completely. The gap also shows considerable brightness if the
energy is not taken up by the secondary, or meets with a high
impedance (out of phase reflection from the secondary aka out of
tune). Because of the ion-cloud and spark adding to secondary
capacitance with neither one of these things being set in concrete,
perfect tune under non-spark conditions <> perfect tune under spark
conditions. So tuning the primary lower in low-level tuning is needed.
In fact the formation of the ion cloud actually causes the secondary
to "pull" itself into tune with the primary if this is done
(parametric tuning).
Just like to say thanks for listening to the above verbosity. I
promise I've said my last word on this. In fact I have arrived at my
conclusions both from observing gap behaviour under different load
conditions and also from observing captured waveforms under those
load conditions. The two correspond exactly. I know that most people
don't have access to this kind of test gear, so I am doing my best to
make what I learn from this available. In doing so, I can't avoid
presenting some conclusions that the measurements lead me to. Some of
the above could possibly have been better worded. Also, apologies for
spelling out what is obvious to some.
I am open as always to criticism of my views.
Regards,
Malcolm