RE: Frequency splitting (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Tue, 21 Aug 2007 08:41:42 -0400
From: "Lau, Gary" <Gary.Lau@xxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: RE: Frequency splitting (fwd)

Thank you Bert - I always look forward to and save your posts.  I wholly
agree that there must be capacitance between the conductive plasma
channel and the rest of the world, in the same way as there would if the
arc is replaced with a piece of wire.

But if I may play the devil's advocate for a moment - I recall about a
year ago when Terry and others were playing with streak cameras, the
duration of arc luminosity was extremely brief.  Is the plasma
"conductiveness" correlated with the luminosity?  In other words, is the
effective increase in Csec due to the plasma channel, in effect for the
entire bang duration, for only for a few nanoseconds during each HF
peak, or does it span bangs?  I'm sure the answer is a great deal more
complex than any one of those answers, but I have to wonder what the net
effect would be if the channel capacitance were present for just a few
nanoseconds per bang.

Thanks, Gary



> From: Bert Hickman <bert.hickman@xxxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: Re: Frequency splitting (fwd)
> 
> Tesla list wrote:
> > ---------- Forwarded message ----------
> > Date: Sun, 19 Aug 2007 15:22:28 -0400
> > From: Jared Dwarshuis <jdwarshuis@xxxxxxxxx>
> <snip>
> >
> >
> > Commentaries:
> >
> >
> >
> > It has come to my attention that many experts on Pupman are now
describing
> > the plasma arc from the secondary capacitor  as having a
capacitance. They
> > are tuning coils as if the capacitance was really there.
> 
> One might reasonably ask where the currents flowing through the roots
> Tesla Coil air discharges ultimately "go"? The answer is that, unless
> these discharge actually complete an arc to ground, all of the current
> flowing through the "root" of a TC air discharge is ultimately due to
> capacitive charge transfer (i.e., displacement currents) since there
is
> no direct or resistive path to ground on the far end.
> 
>   >
> > There is no such capacitance in the arc. Capacitors do not increase
> > capacitance when they arc out. Arcs do not have an ability to store
charge.
> > Arcs  do not have plates nor can they be described with a fixed
geometry.
> 
> Unfortunately, you are artificially limiting the physical definition
of
> "capacitance". Any conductive object has the ability to store and
> transfer charge. This includes toploads, a projecting length of wire
> from a topload (the effects on tuning being easily measurable), or a
> similar length Tesla Coil discharge springing from the topload.
> 
> The easily visible part of a TC discharge is only part of the total
> discharge. Most of the actual charge transfer process occurs at the
far
> ends of the sparks, in the dim bluish colored region just beyond the
> leader tips. In this region, countless microscopic filamentary
streamer
> discharges busily transfer charge into, and out of, thin air - into
and
> out of the invisible "space charge" regions that form around Tesla
Coil
> sparks. The cumulative result of these filamentary streamer currents,
> when combined through various leader branches, is a significant
> (multi-ampere) displacement current that flows through the root of the
> main channel.
> 
> There are also voltage drops along the plasma paths from (nonlinear,
> arc-like) channel resistances. Even though the discrete processes are
> considerably more complex and operate across time scales spanning at
> least 6 orders of magnitude, at a macroscopic level the channel can
> simply be modeled (for most TC purposes) as a distributed resistance
in
> series with a distributed capacitance, each scaling with overall spark
> length.
> 
> In 2001, Terry Fritz measured an effective spark "load" of about
> 220k/foot and 1.9 pF/foot. Although YMMV based on coil size and power
> level, this seems to be in the ballpark for disruptive Tesla coils. A
> similar degree of detuning can easily be measured (by attaching a
> suitable length of wire from the toroid and using a signal generator
to
> find the loaded resonant frequency of the secondary (emulating the
> effect of the capacitive loading by conductive plasma channels).
> 
> >
> >
> > Nor can we describe an arc as having an appreciable inductance. The
geometry
> > is not much good for inductance.
> 
> I agree that path-associated inductance has little bearing on low
> frequency behavior of the coil (i.e., TC tuning). However, leader path
> inductance does limit the charge transfer rate between HV terminal and
> streamer tips during the nanosecond-scale current events that
> characterize actual streamer growth. More accurate dynamic models for
> leaders and streamers do include include distributed inductance,
> capacitance, and channel conductivity. Channel inductance also comes
> into play during direct toroid-ground discharges.
> 
> >
> >
> >
> > Nope!;  you are altering C or C'  to make up for changes in
frequency caused
> > by dampening. (dampening from  the non linear resistance of the arc)
> >
> >
> >
> > Empirical corrections are wonderful, my hats off!  I am sure that a
great
> > deal of effort was involved in arriving at a useable correction
factor. But
> > there is no capacitance in the arc. There is only non linear
resistance and
> > perhaps a tiny bit of inductance.
> >
> 
> OK... Let's assume that leaders are merely nonlinear resistances. What
> is tied to the "other end" of the current path? How do you (otherwise)
> account for multi-ampere air streamer currents on one, seemingly
flowing
> into thin air at the other end?
> 
> >
> >
> >
> > Jared Dwarshuis  August 07
> >
> >
> 
> The roles of pulsed charge transfers, displacement currents, and
> streamer capacitance are included within the "streamer theory" of
spark
> propagation. The streamer model, originally developed in the 1930's,
has
> been experimentally verified and refined by countless researches in
the
> intervening years. It is now accepted by virtually all serious spark
> researchers. The streamer model appears to apply to the formation and
> growth of any long spark within a nonuniform field, not just sparks
from
> Tesla Coils. A couple of excellent resources that cover spark
> propagation in much greater depth include "Spark Discharge" by
Bazelian
> and Raizer (ISBN 0849328683) or Gas Discharge Physics by Raizer (ISBN
> 354019622). You can also find tons of information by searching the
> literature for "streamer capacitance", "leader capacitance", or
> "streamer model".
> 
> Bert
> --
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