Re: Stealing Celestial Fire

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Jim Lux" <jimlux@xxxxxxxxxxxxx>

I like the off hand comment:
"they are far from getting filaments that could span the 5 to 6 kilometers
separating a thundercloud from the earth"

They sure are a long way from doing it (as in tens of orders of magnitude).
they get 3.8 meter filaments now. Leaving aside the challenge propagating a
high power laser beam for several km (without distortion), made much tougher
by the very short pulse (implying wide bandwidth, and meaning that the
frequency dispersive effects of the atmosphere are of importance).

You're left with the common feature of all directed energy beam systems: the
fact that inverse square law means that ionizing that 3.8 meter segment a km
away as opposed to 10 m away will require 10,000 times the power.  (the
segments 5 km away will require only 250,000 times the power)  At least
you'll ionize an area that's 100 times the diameter.

Finally,  they still have to ionize a path some 1000 times longer, so the
energy has to be increased by the same fraction.


Interesting, also, that they aren't getting a huge reduction in breakdown
voltage with this system.  3.8 meters isn't all that far to jump for a rod
gap at 1-2MV. The filament is being created in an area where the field is
already close to breakdown.  (or, maybe, they are doing it right, firing the
laser, waiting for the filament, then triggering the marx).  Typical fields
before a lightning strike are in the 20kV/meter range... a long long way
from 3MV/meter free air breakdown or the several hundred kV/meter if they're
firing that Marx into a uniform field gap.

A rod/plane gap (as described in the article) probably looks a lot like a
rod/rod gap twice as long, field wise.  1m standard rod gaps breakdown at
500-700 kV.  A 3m rod/plane gap would be like a 6m rod/rod gap, but as shown
in Bazelyan and Raizer, when there are nonuniform fields, you can't just
extrapolate up... The breakdown on that 3.8 m rod/plane gap is probably a
couple megavolts, at most.


They employed their Teramobile laser, whose pulse lasts for a mere 100
femtoseconds and packs a peak power of 5 terawatts

That's 100E-15 seconds * 5E12 Watts = 0.5 Joules... if I got my prefixes
right...

Now.. they're using the high Efield to ionize the air, but not dumping much
energy into it.  That means that when the pulse ends, the air isn't hot, and
won't stay ionized very long.   They'd have to simultaneously ionize ALL the
column to make this work (it's not like a traditional spark growth scenario,
where the current flow into the leader heats the air, so it's thermally
ionized).  It's possible that they could ionize in 100 meter chunks (much
like real leaders and lightning). That is, use the laser technique to
"guide" the development of an existing lightning leader already forming.
Lightning leaders move fairly slowly, compared to light, so conceivably, you
could detect the formation of a leader, determine where to aim the laser,
and fire, to force (or push) the extension of the leader in a desired
direction.  The detection process is non-trivial, but at least it depends on
EM propagation, so it moves at light speed, as does the return laser beam.

Yes... I'll say they've got a ways to go.

But it is cool and nifty, none-the-less.
----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, April 20, 2005 12:25 PM
Subject: Stealing Celestial Fire


> Original poster: "Samuel C. Johnson" <metaform@xxxxxxxx>
>
> If anyone is interested in reading the article published in the IEEE
> Journal, you may read it at:
>
>
<http://www.spectrum.ieee.org/WEBONLY/resource/apr05/0405nlas.html>http://ww
w.spectrum.ieee.org/WEBONLY/resource/apr05/0405nlas.html
>
> Sam Johnson
>
>