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RobertDyck

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From: Winnipeg, Canada

Registered: 2002-08-20

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Light sabre - how to

The new Star Wars movie is out. Time to geek out.

A couple years ago a friend described his idea how to build a light sabre. He claimed he put up a page on his personal website in the early 1990s. Then a few years ago got a phone call from someone claiming to be from the US military, demanding to know how he got their latest super-secret combat knife. Uh, huh. No one believes him. But it makes an interesting start.

His idea was to start with an atomic battery. That requires plutonium. He claims there's a way to redesign the battery to produce more current, just by making certain layers of the power converter thicker. He said standard atomic batteries produce high voltage and low current. Uh, huh. Well, it's nice to fantasize. So the handle is the power source, which is nuclear. Next he suggested a small bottle of water. Some water would be heated to plasma, producing a plasma jet. This plasma jet would act as a plasma cutting torch. The catch is the blade would only be as long as a knife blade, not a sabre. And you would have to refill the water bottle every so often, but water is easy to obtain.

But we want an actual Star Wars light sabre. How? The plasma window is a sheet of plasma so viscous that it can hold in air pressure. It was originally designed for an electron beam welder, that requires vacuum to generate the electron beam. But a welder must produce a beam strong enough to melt metal, so how do you get the beam out? His solution was a plasma window. If the plasma gets hot from the electron beam, that just holds out air better. The catch was it requires 20,000 watts per inch diameter, and the plasma must be at least 12,000°K. Researchers studying plasma windows today use 14,000°K, so that if something touches the plasma and cools it down, it will still be above the critical temperature required to keep it viscous. The original plasma window could hold out 1.5 atmospheres of pressure against hard vacuum. Ok, so we have a plasma that is hard, can burn through an enemy arm or metal post, and can stop laser blasts.

So how do we columnate the plasma to form a sabre blade? Astronomy describes a very large plasma jet coming out from the super massive black hole at the centre of some galaxies. The rotating accretion disk causes magnetic field lines to twist into a column. And that columnates the plasma jet. Interesting! Could a strong magnet in the end of the light sabre create such twisting magnetic field lines? Interacting with a jet of plasma as hot as a plasma window? Could a twisting magnetic field be generated electrically, or would the magnet have to physically rotate?

Then how do you limit the length of the sabre blade? If it's a plasma jet, do you create a fountain that reaches a certain limit then flows back? A water fountain in a shopping mall shoots water up so high, then the water jet can no longer fight gravity, and falls back. Could a plasma jet be designed to shoot a certain distance then fall back into the handle? Could that be controlled, and plasma recirculated? Or would returning plasma splash all over the person wielding it? Would a collection pool have to be huge, like the pool of a shopping mall? Or could the plasma collection pool be small, like the quillion (crossguard) of a sword? Would plasma counter-flow screw up the magnetic twist that columnates the plasma jet?

This is a very complicated plasma calculation.

Terraformer

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From: The Fortunate Isles

Registered: 2007-08-27

Posts: 3,906

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Re: Light sabre - how to

I suspect it would be much more easier to have a retractable (?) wire, that would be held out and rigid by the magnetic force caused by the current flowing through it (much like a magsail). Then, use that to control the plasma around it. Or if it's hot enough, create the plasma. Whatever way, you're looking at a tungsten filament, which is going to have to retract into the handle very soon after switching it off...

Unless, of course, you can use a cool plasma, maybe 750-1250 kelvin. It would still be hot, but hopefully you can keep the plasma from touching the wire?

It would be quite a thin lightsaber, in any case.

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Use what is abundant and build to last

RobertDyck

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From: Winnipeg, Canada

Registered: 2002-08-20

Posts: 7,933

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Re: Light sabre - how to

Another issue is temperature. Good guys had a blue sword, bad guys red.

Old TV westerns had good guys wear white stetson hats, while bad guys wore black hats. A simple way for the audience to relate. Of course in real life it's never that simple. In fact, often the guy identified as "bad guy" doesn't think of himself that way. He thinks he's the good guy. And perhaps you should think about that before taking action. Before you do something for your job, are you the good guy? Or are you the bad guy? Guards at the Nazi concentration camps during World War 2 were just doing their job. As they rounded up Jews into cattle cars on trains, with no bathroom and no water or food, locked in the car for days, they were just doing their job. As they rounded Jews into gas chambers for extermination, they were just doing their job. The Nuremberg trials established the precident that anyone given an illegal order is not only allowed to refuse, they're required to. If an illegal order is given, the officer or person in authority is guilty, regardless whether he/she is present when the offence is committed. That person in charge (manager or officer) is not just guilty of conspiracy, that person is guilty of the act. But they also established the precedent that the subordinate is equally guilty. So yes, the guards at Auschwitz were guilty of mass murder. Think about this when your ordered to do things at work.

Ok, too deep for a movie inspired discussion. Colour of the light sabre. Plasma colour is determined by temperature. I suggested for the sabre to act as a physical blade that can stop bullets, or laser beams, or blaster bolts (which don't appear to be simply lasers) then the plasma must have some physical presence. A viscous plasma like that of a plasma window would have such a physical blade.


This means a viscous plasma will be blue. Jedi light sabres were blue, Sith red. That would imply red light sabres were lower temperature, so more energy efficient. They could engage in combat longer on the same power cell. And a temperature between 1,000°K and 2,300°K (roughly) would still do a lot of damage. But that means a red sabre couldn't block a physical object like a bullet. A red sabre relies on burning through everything it hits. A red sabre could still parry because the magnetic field of the blade would repel the magnetic field of his opponent's sabre.