Slashdot Mirror
Rail Guns Closer to Reality
emtboy9 writes "Yahoo News is reporting that scientists at Sandia National Labs have created a magnetic pulse gun (rail gun) that can accelerate small aluminum plates at 34 kilometers per second, faster than the Earth travels through space.
The accelerated plates strike a target after traveling only five millimeters, or less than a quarter-inch. The impact generates a shock wave -- in some cases, reaching 15 million times atmospheric pressure -- that passes through the target material turning matter into various states almost instantly (solids into liquids, liquids into gas, and even gas into plasma)."
However -- rail guns are on the cusp of military viability. The University of Texas at Austin's Institute of Advanced Technology got 10 million dollars to develop viable rail guns. Just a month ago Janes reported that a prototype of the military rail gun had been tested, and that it was nearing viability.
That article really made me wish I had a Jane's subscription. Apparently, the limiting factor is the size of the capacitor -- if they can get this down than naval applications within a few years are plausible.Incidentally, a fun game, if you're ever bored, is to imagine what would happen to the human body if one were to hold and fire a rail gun (even a wimpy one that shot at a mere 1,600m/s and not at "near the speed of light"), and the law of conservation of momentum actually worked. Really! Try at parties!
Fond wishes,
Moiche
This is the huge tidbit that I haven't really seen discussed: "That's 50 times faster than a rifle bullet, and three times the velocity needed to escape Earth's gravitational field." A rail gun, of sufficient capacity to catapult raw materials into orbit, would be a gigantic breakthrough for the whole planet.
The Z machine (and it's earlier configuration called PBFA 2) have been on Sandia for a long time.
As said above, it's not a rail gun. It's not really even particularly useful for rail gun research.
What it's for is to put small amounts of matter at tremendous temperatures and pressures.
There are a lot of reasons to want to do this. Some of it is just basic research. i.e. What happens to matter and the laws governing it at these extreme conditions?
Another application is fusion power research. You can compress deuturium and tritium to the point they will fuse in this machine. Though it's not made to generate power, you can learn about the details of the fusion reaction.
That said, the main reason why this machine was built was indeed for military research. But even that is in a grey area. The US hasn't conducted a nuclear test detonation in quite some time. The reason it was able to do this is that computer simulations and other methods got good enough that they were able to be used instead of actually setting off a thermonuclear or nuclear device. Indeed, many of the Department of Energy's most powerful computers were created specifically to do that sort simulation (ASCII White, IIRC, for example).
When running computer simulations, you have to have some way of calibrating the simulation and checking that it's getting the right answer.
In the case of a supercomputer run simulating a car crash, you can validate it by conducting crash tests, and seeing how closely it agrees with them. Wrecking a few of a given car model is acceptable in return for it.
But, when simulating nuclear weapons, you would often run into cases where to validate the code, you'd, at first glance, have to set one off. The conditions in a nuclear blast are so extreme, that it's difficult to put matter into that sort of state. If you're trying to maintain a test moratorium, that kinda undermines the whole idea.
That's a big reason PBFA 2 and the follow on Z machine were made. They let DOE check the computer simulations and do basic research that would otherwise require nuclear testing. One of the biggest areas of interest is what happens when the materials in a bomb age. A lot of those weapons are getting quite old.
They have many other basic research uses, but a big one is making it possible to keep the nuclear test moratorium.
So, it's grey area. On the one hand, it's used for weapon research. On the other, it helps keep the test moratorium. It also has a lot of basic research uses. So, just like a supercomputer, you have to make your own decision about whether it, on the whole is a good or bad thing.
Powering spacecraft or launching cargo or many other things...
How am I supposed to fit a pithy, relevant quote into 120 characters?
Rail guns are unlkely to be useful for driving implosions. It would be very hard to focus a symmetric implosion with a railgun. However, you could use the same pulsed power to drive an implosion like a plasma gun. Get a thin gold tube, fill it with DT, and whack in a pulse. The pulse goes up the outside of the tube. The gold outside goes directly to plasma, stops conducting, and so the current can move inward. If you can get the shockwave reaction from the expanding plasma to approximately match the speed of the current penetration, then a nice, cylindrically symmetrical implosion should be yours, and the small burst of annoying penetrative radiation and the hair loss that goes with it.
There is another effect - the Z-pinch - that is a bit railgun-ish. This gets a lot of mention in the Sandia webpage. People used to have great hopes for that - it was quite the thing in the seventies, when people could still use phrases like 'everlasting power from seawater' without laughing - but it is hard to get a symmetrical pinch before instabilities run riot.
Don't take my word for it. Maybe, I'm too old, and things have moved forward since I last was in this field. Sandia is a seriously cool place, even if the people who write their webpages are a bit too keen now and then.