Lightning vs. Tesla Coil Discharges

Hi All,

While reading Jim Lux´s answer to my post on filming
TC arcs, a few questions popped into my head:

While coils can be (and ARE) very impressive, I´m sure
all will agree lightning is the hands down winner, when it
comes to the *really* impressive discharges.

What is a cloud in the sense of source? Is it *just* an
ultra high voltage source or is it a high current source? I
would guess the latter, because the plasma channels
lightning creates can easily be several inches (maybe
even feet) in width. This discharge channel gets so hot
that we can hear the air being displaced (the thunder).
Wouldn´t a Marx generator be a more *exact* equivalent
of man-made lightning?

What capacitance (roughly of course) does a cloud have?
Is the impedance and capacitance of a lightning strike
comparable to a TC discharge? Terry found that these
values are (more or less) constant for small table top coils
and even for the big monsters that Greg Leyh, Jeff Parisse
and Bill Wysock build. Would they be similar for a lightning

>Current keeps flowing because once the channel is
>formed, it's resistance drops dramatically (that
>negative V/I curve).

This might well be the reason why a TC will almost always
perform better with a larger toroid. The more Ctop, the
more current (and not voltage) our TC can deliver to the
arc channel. Maybe it is also the reason, why low voltage
(high current) powered coils don´t perform worse than
hv coils do ;o)).

>Eventually, IR losses will be enough that it can't
>extend, and inevitably, it cools down and disappears.

One way to cheat this would be to use an easily ionizeable
gas like argon, helium, etc and construct a pre-defined
channel (like a plastic "hose" out of some kind of clear
material) that the discharge can follow.

>The random dendritic nature of the spark means that it
>is branching out as it goes (even if most of the side
>branches are very short and don't go anywhere), which
>consumes ever more charge and current to keep the
>whole thing hot, as it gets longer.

>Once the channel has reached 7000K, the conductivity
>is so high that the IR heating drops off.. Essentially, the
>entire leader is "regulated" by a sort of negative feedback
>(heat loss proportional to T^4, heat input proportional to
>I^2R, which is inversely proportional to temperature) to a
>temperature just high enough to keep it "well ionized". So
>the point where two leaders meet is probably no hotter
>than anywhere else along the leader.

This brings another thought to mind. What would happen
if we could (in some way) make a discharge path which
is surrounded by a gigantic magnetic field? This should
keep the plasma bundled and very hot. What would happen
if we constructed this magnetic field similar to a coil gun? In
other words using not one, but several magnetic coils along
the discharge path. Could one accelerate or even stretch
the actual coil discharge?

Thanks for the explanation of the image intensifier. The only
ones I have had contact with, were the ones we used during
my stay in the Army. These had a long lasting phosphor screen,
which blurred the image, if you followed a fast moving target.

>Now.. I don't know if the surplus $500 night scopes have
>this sort of high speed performance.. They certainly have
>low resolution (mostly a function of how many channels
>there are in the intermediate amplifier stage)

Most surplus night scopes are ones that have been rejected
by the military and usually they will have several "dead" spots.

Coiler greets from Germany,