Directions for tesla coil research

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

I've been thinking a bit about how best to study the spark growth
interaction with current and voltage on the topload... more
straightforwardly, how to get the best sparks.

It seems that there is a huge dependence on the voltage and current on the
topload.. So.. to do some quantitative studies, here are some ideas:

1) Driving a primary with a suitable arbitrary waveform generator.. you
could control the excitation to carefully adjust things like bang rate,
frequency, etc.  Maybe you'd really want a non resonant system here...
Insulation might be a challenge, but, for thinking purposes, imagine a
1000:1 transformer with very tight coupling driven by the ARB connected to
a topload. Certainly, insulating for a megavolt is entirely possible.
Building a suitable high power high voltage driver for a kilovolt is a
challenge, but not inconceivable...  

1a) How much does the Cself of the secondary contribute to the spark
growth, or is it safe to assume that Ctop is all that really matters, given
the high impedance of the secondary especially for fast time scale events.
One way to look at this would be to put a current probe on the secondary to
topload connection... Guesses as to the current here? (should be of the
same general magnitude as the base current, right?) You could put the probe
in a electrostatically shielded enclosure (inside the topload comes to
mind) and get the info out via fiber, or just log it digitally, and
retrieve it "off line"

2) What's the minimum size for a highly instrumented system?  How can one
best address scaling issues?  One would like to do testing on a fairly low
power smallish coil... You don't want to have to build a 10 kW driver, you
want to be able to run it in a very controlled environment (i.e. a cage), etc.

3) Could one build a suitable means to measure the actual spark/leader
current.  There is some literature on this.. You would create a breakout
point that is somehow connected to the topload by a VERY low impedance
connection... Could one, for instance, measure the voltage drop across the
surface of the toroid using an array of probes? (from the inside) Does some
form of magnetic sensor allow you to measure the leader current?  This has
to be a really wideband measurement (hundreds of MHz).

4) High speed photography and recording.  What's a good way to get properly
synchronized high speed imagery?  Modern CCD cameras have shutter speeds
that are fairly fast (100 uSec or better), but that's probably much too
slow.  Good ideas on microsecond shutters (or is the technology still
things like Kerr and Pockels cells)?  What about modifying an off the shelf
image converter night vision scope (fast pulse on the cathode, for
instance.. might be easier than fooling with nitrobenzene in a Kerr cell)

This is all pretty exotic... What about simpler stuff.. Triggered gaps
running off a DC supply with a big charging choke/resistor can give good
control of "bang" timing.  Say you set up a field probe with a simple
sample/hold at some distance and then average up thousands of bangs...  How
consistent are things like the leader step timing?