Re: Lightning vs. Tesla Coil Discharges
> 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?
The latter, a high current source, many coulombs at many volts, but mostly
a current source (roughly 10 to 100 kAmp) dissipating about 100 kJ/meter of
length. Yes, which is why impulse generators like Marx banks are used to
simulate lightning for component testing.
> 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)).
I think this is true...
> >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.
This has been done... More than one person has rigged up a nozzle to shoot
a stream of argon out the top of a TC. The Corums rigged up a scheme which
shot a stream of fine metal particles, along which the leader moved,
creating a good "death ray" type effect.
> >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.
> 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?
Yes. Magnetic fields are used to compress and to stretch arcs. Some large
circuit breakers use the fault current to
"blow" the arc into a set of disrupting plates.
> Most surplus night scopes are ones that have been rejected
> by the military and usually they will have several "dead" spots.
But might still work for this sort of purpose?