Cecil Moore wrote:
On Oct 18, 11:30 am, Jim Lux wrote:
You can model a tesla coil's
behavior to within about 5% using a simple lumped LC model.

How can a model that presumes faster than light speeds yield a valid
outcome? Drs. Corum seem to disagree with you. Here's what I have been
quoting:

http://hamwaves.com/antennas/inductance/corum.pdf

Drs. Corum seem to debunk the lumped LC model. They also once had some
class notes titled: "Tesla Coils and the Failure of Lumped-Element
Circuit Theory", but I can't locate it on the web.

Changed the topic.. and really, this isn't r.r.a.a territory any more..
Feel free to send me an email directly.

This has been thrashed through pretty thoroughly on the Tesla Coil
Mailing List (TCML, http://www.pupman.com/) and I'd refer interested
parties to the list archives, or, to the works by Paul Nicholson.


I've had some nice discussions with Corum the younger, but, their model
makes life harder than it needs to be. Occam and all that.

At TC resonant frequencies (100kHz), the "light time delay" from top to
bottom of a 3 foot high coil is pretty small. I don't know about faster
than light, but at 100kHz, for an object that's a meter or two in size,
assuming simultaneity isn't a big stretch.

(for the propagation of the spark, though, and the current flow in the
top load, yes, the speed of light matters, and in fact, the speed at
which the charge can get off the top load and into the spark channel is
probably one of the bigger factors affecting maximum spark length.)

People have also put current and voltage probes at the top and bottom of
the secondary coil (with fiber optic connections etc.).

Getting to the "transmission line" or "slow wave structure" aspects..

You've got an inductor with a lot of stray distributed capacitance.
Indeed, that's exactly what a transmission line can be modeled as
(distributed series L and shunt C). And with an arbitrarily complex
nonlinear distribution of L and C, you can make a transmission line that
acts like a lumped L and C of the appropriate values.

So, the question really is, do you want the simple model or the complex
one. If the goal is to design better tesla coils, and the simple model
gets you to fractions of a percent in terms of agreement between
experiment and theory, why use the more complex model. It doesn't lead
to any better understanding of how it works, either.


Now, if you want to talk about modeling the spark channel as a time
varying lossy transmission line, that's something more interesting, and
it DOES have value in terms of understanding/predicting the behavior.
For that, I'd point readers to "Spark Discharge" by Bazelyan and Raizer,
which is one of the best works in the field, and a fascinating read
(and, as well, they have that cool 150 meter+ spark picture from a
really, really big Marx generator, 1.2 MJ or more, in Siberia)