Question on electricity and light (physics)

[Ashton]

I was thinking about a concept from an old Sci-Fi book ("Invaders from Regil", if anyone's familair with it) and was wondering if anyone here knew the physics to either tell me how it can be applied or that it's impossible. From my standpoint of very limited advanced-sciences, it seems possible but unlikely...

In the book, the characters had built a 'plane' that collected static electricty as it flew, like a mason jar, then, they used a high-intensity light and electrodes attached to the casing, to direct the stored electricity, saying that it woudl follow the beam of light instead of purely going from sky to ground like lightning.

Does anyone know if this is real or just Sci-Fi? If it's real, what's the science behind it and could it be incorperated into a laser? (and if so, how pwoerful of a laser and of a power source would be needed?)

 

[chuckknight]

Hmmm...I'm not entirely sure what the purpose of such a device might be, but let's just say you want the electricity to follow a beam of light.

A Blumlein LASER (UV LASER using atmospheric N2 as a lasing medium) will ionize atmospheric nitrogen as it travels...and at its power levels it will do it over a significant distance.

Since ionized air offers a less insulative path than regular air, it creates a conductive pathway...an electrical discharge would follow the path of least resistance.

I was on an alt-science forum a few years back, and we theorized that lightning might create its own conductive path in this exact way. And, that tapping clouds for power (cloud = conductive plate, earth = conductive plate, air = dielectric) might be practical, using this very method.

It was a fun theory...but certainly nothing I would ever test. Whoever tested it would *literally* be drawing down a lightning bolt, directly into their equipment.

-- Chuck Knight

 

[pseudonomen137]

Yes, there was a post on LC just a few days ago with a vid showing that. In high enough powers the lasers can ionize air forming a conductive path for electricity - just like dielectric breakdown of air but without needing the high voltages. Not sure of the power, but it takes a decent bit. I think people have done this with focused SSY-1s before, but its not something you do in any regular setup.

 

[Hemlock_Mike]

The SSY-1 if focused to a sharp point will ionize air and cause a kind of plasma flash and snap in front of the lens. I've done it with mine at about 18 Joules and a 2" FL lens. A plasma is highly conductive as in plasma arc cutting but we're talking killowatts to do this.
Nitrogen can be used to make a spark gap UV Laser. Perhaus a goodly amount of UV laser might cause the N2 in the air to ionize easier.

Mike

 

[Ashton]

ok, so... translation: For all practical purposes this is still Sci-Fi.

I was thinking of basically like a taser, you aim the beam, throw a switch, and electricity flies down the laserbeam and strikes the target asif it were struck by lightning. Though using it to call down lightning for charging batteries to somthing is a fun idea, if probably impossible (or atleast impractical)

But, practicality aside... just how much power is this requiring? I looked us SSY-1s on Sam's LAser FAQ and they were talkigna bout them barely putting out enough pwoer to smoke electrical tape! my 135mw pulsar can do that! (I'm not familiar with Jeules, how much power are we talkign in mw/Ws?) Even if it does require a labby, that's an awesome concept lol

 

[Aseras]

the ssy-1 is old technology. it's flashlamp driven. it's only good for pulses, if you actually wanted to burn something you really need MUCH higher powered pulses or a CW application. for the cost of a whole ssy-1 setup from scratch, you can have a co2 laser that's a thousand times more powerful and full CW.

for ionization you actually want to go down in wavelength, then you have a smaller wavelength, and more energy. A uv laser like an excimer can easily ionize air in CW mode. an experiment I remember was to have a van de graff generator ( static electrical generator ) build up a charge and fire a excimer through a metal plate ( shield the laser frrm discharge ) across the generator head and to a ground rod. the electricty would arc along both paths of the beam. it was kinda neat.

there was also a study a while back ( don't remeber who i think japan? ) where they tried to stimulate a thunderstorm with a very high powered excimer uv laser to stimulate a lightning strike.

 

[Ashton]

After reading about the Excimer on wikipedia, it terrifies me that I can buy one on ebay... (granted it's $2000, but still...)

I really, really, really, really, REALLY dont want to play with UV light... IR can blind you, but UV can give you cancer...

I'm still not seeing a power rating... I've seen Co2 lasers in the 10W for a few hundred, would this do that, and if so, how would you protect the laser from the 'lightning' (aseras said osemthing about firing UV through a metal plate...? metal, I thought, absorbs light, so how could you make it pass through (or was it a fine metal grill?))

This hobby keeps giving me deviously wicked ideas for projects... I wonder just how portable a vandegraph is....

 

[SenKat]

You can make a van-de-graff from a soda can - so it is pretty portable !

 

[pseudonomen137]

Some of the laser stuff you're asking about may be a little overambitious to start with. What it sounds like you may be interested in though are transformers. You can pick up cheapo NSTs (Neon Sign Transformers) for <$50 that can be run off batteries (if you stick enough in series/parallel) and ionize air to general a constant arc >1". After that you may want to look into Jacob's ladders. Dangerous stuff and you wont want to play with it until you know the dangers involved, but a whole heck of a lot cheaper than the laser things you're talking about.

 

[Ashton]

lol. This is just a silly idea I had taken form a number of sources. To reduce it to absolute layman's terms, I want a lightning gun. No, I dont have any malacious intent, just pure 'cant this be done? I did it!' type thing.

 

[pseudonomen137]

Not entirely impossible, but portability would be severly limited by the extreme power requirements, and operation would probably be limited to a femtosecond pulse. Also wouldn't be able to fire at ungrounded targets .

 

[Ashton]

I'm still working on aquiring the parts needed to portabalize a 10W Co2. (including the massive backpack needed to hold the PSU and batteries) I was thinking this might be a fun add-on when CO2s were mentioned, but I'm starting to see the science behind this. I'm guessing also I'd need a rather large vandegraph to draw a spark that's 4' long.

Grounding isn't a problem, as I said this has no malcious intent, so I'm planning more on driving a long metal rod into the ground and attaching a flat plate to the front (sorta like a street sign) with the vandegraph a few feet from it, and the laser would fire through the ES Charona (probably not the right terms, but) and the lightning would leap from the vandegraph to the grounded "sign" a few feet away. (yes, this is a semi-permanent demonstration I'm wanting to construct)

Biggest problem is the power requirements for laser and gennerator, and, more importantly, how to keep the lightning from going from gandegraph to laser and blowing it up... So far outside of placing a ground wire withint he laser beam (and @ 10-80W it owuld have to be made of something with a VERY high melting point so it doesn't start liquifying on me) and I'm not sure that even that would work... if the spark length is less than the distance between laser and gennerator, would the electricity be forced to take the opposite path or would it still hit my lasertube? (i.e. sparks average 4' and laser is set up 8' from gennerator)

EDIT:
and I'm not expecting continual arks, while that owuld be nice, just a nice visible pulse like a lightning bolt is all I'm expecting.

Oh and yes, I am also planning to eventually build a jacob's ladder, just not untill I have an area free of pets... kentucky-fried-kitty does not appeal to me...

 

[SenKat]

I am going to go on and move this to the "experiments and mods" section...sorry if it offends you by doing so !

 

[Ashton]

I am going to go on and move this to the "experiments and mods" section...sorry if it offends you by doing so

The thread evolved, I started out with a genneral question and am now moving into planning a project, it makes sence to move it.

Also, While reading about how to build a vandegraph, I noticed that its construction is very similar to a plasmaball (which runs off a teslacoil) Is this coincidence or are the two related?

 

[pseudonomen137]

Well, I still don't think the CO2 backpack is the best idea - besides making power and cooling portable, a fragile large tube is not the ideal solution for a handheld - but anyway.

You're right about the plasma ball and van de graff though - its the same general idea of using a high potential difference to ionize a gas.

As for your project, I think you should keep it purely electrical. Bringing the laser in, as cool as it would be, is not practical for your budget. A 10W CO2 would be a nice burning laser, but in both wavelength and power its orders of magnitude off from what you'd need to ionize atmosphere and guide a 4' arc.

For a 4' spark on a Van De Graff you'd probably need at least 1 foot radius on the electrode (probably a bit more than that)

 

[Hemlock_Mike]

I don't think 10 W of CO2 would ionize a 4" path unless VERY tightly columinated. My SSY-1 can only do it at a tightly focused point.
A small hole in the grounded plate should be sufficient shielding for the laser especially if battery powered and not grounded. My plasma cutter has to have the metal being cut grounded to the machine or no arc with power is established.
The other problem I see with a "lightning projector" is that the source is also part of the circuit - That's you !!!
Mike