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Modern take on Franklin's lightning-kite experiment?
Posted: Wed Jan 19, 2011 7:51 pm
by chrismb
All you engineering chaps, can you answer me this? If I stand under a thundercloud and shine a laser (or maser) up at the cloud so as to create a preferential channel of ions that the static charge can rush down, how powerful does that laser need to be?
Posted: Wed Jan 19, 2011 9:20 pm
by rjaypeters
Check with the University of Florida. They do lightning research for NASA, in Florida, runner-up lightning capitol of the the world. Don't know if they use(d) laser to trigger, mostly rockets, IIRC.
Posted: Wed Jan 19, 2011 9:34 pm
by Giorgio
Here you go:
http://iopscience.iop.org/1367-2630/4/1/361/fulltext
This model suggests that UV (220-420 nm) 200 ps laser pulses with a peak power of around 50 MW (or 12.5 mJ input energy) and a beam size of 100 µm are the optimal tool to trigger outdoor lightning. The laser beam size remains relatively small (less than 0.3 mm) after a propagation distance of 200 m up into the normally cloudy and damp atmospheric conditions.
Posted: Wed Jan 19, 2011 9:51 pm
by Diogenes
From my reading, there are at least two companies working to use laser generated plasma channels to produce a long range Taser weapon.
Cool idea, but I can see serious problems with it if criminals get a hold of it. Rape and robbery would be easy if you can zap someone into helplessness from 300 meters away.
Posted: Wed Jan 19, 2011 10:25 pm
by DeltaV
Another piece of the puzzle falls into place...
viewtopic.php?p=44778&highlight=#44778
Posted: Thu Jan 20, 2011 12:14 am
by ladajo
rjaypeters wrote:Check with the University of Florida. They do lightning research for NASA, in Florida, runner-up lightning capitol of the the world. Don't know if they use(d) laser to trigger, mostly rockets, IIRC.
They do (did) lightning research at Stennis Space Center as well. When I was working out there, as I recall they were mucking around with poles and rockets.
Posted: Thu Jan 20, 2011 4:34 am
by DeltaV
And they just happen to have engine test facilities there...
Posted: Thu Jan 20, 2011 1:11 pm
by ladajo
The engine tests were somewhat awe inspiring. When they would light one off, the swamp would shake for literally miles. Very cool. Gotta love the buffer zone. I liked test days.
Certainly an interesting place to work. Lots going on. I think I miss the "Stennis Speedway" access road the most. Exit 2, then game on...followed with how fast you can transition back to normal space from lightspeed before you clean out the guard shacks. Oh, and lovebug season, can't forget that. But that I did not like so much...
Posted: Fri Jan 21, 2011 8:50 am
by MSimon
Hmmmm. - 200 ps = .2E-9 s. 50 MW * .2E-9 = .01 joule.
The trick is fast discharge. And of course obtaining or building the laser.
Maybe a higher power laser would do if efficiency is not too important. i.e lower ionization per photon.
Posted: Sat Jan 22, 2011 3:48 am
by DeltaV
Posted: Sat Jan 22, 2011 4:28 am
by MSimon
http://www.science-project.com/_members ... 06-fs.html
I would do the power supply with a 12 spark coil, a suitable MOSFET (avalanche rated with heat sink) and a 12 V 555 running at about 400 to 4000 pulses a second. Duty cycle of around 80% to 90%.
Also a HV divider would be good a string of 10 meg resistors with a 10K as the measuring resistor. If 20 KV = 20 V = 100K then the string should total 100 Meg. The divider will draw 200 uA. About 20% of supply power. the 100 K should be made of 2 200K resistors in parallel for safety (in case one opens).