Slashdot Mirror
Sandia Labs Takes First Steps Toward Fusion
robosmall writes "Sandia Labs has successfully demostrated the emission of neutrons (a side effect of thermonuclear fusion) from a BB-sized capsule of deuterium using using their venerable Z-Machine (eye-candy!). With this achievement they enter the race to create sustained fusion reactions."
Talk about a wild desktop background!!!
I mirrored this article, including the images, on my website (a quick one hosted with Yale.edu bandwidth) in case the main link goes down: Here is the Mirror
I'm not sure if I've got all of that right, but I think it's more or less accurate.
My only political goal is to see to it that no political party achieves its goals.
http://www.sandia.gov/pulspowr/facilities/zacceler ator.html
Basically, these guys store a whole lot of electricity in monstrous capacitors, and then shove all of it through a contraption of parallel wires (imagine about a hundred wires lining the inside of a Pringles can -- parallel to the can's long axis -- the "z" axis in cylindrical coordinates, and then take away the can).
From the Lorentz force law (easiest way to see this; alternate explanations work, too, but everything boils down to the same thing), one can see that parallel wires, when they have current going through them in the same direction, attract each other. So these wires, each of which has gazillions (technical term) of Coulombs per second coursing through them -- Amperes), get attracted to eachother VERY much. These attracting wires basically "pinch" whatever is put between them, possibly leading to fusion (in deuterium, the article states).
Now, to add to the complexity, take away the wires. They get vaporized by the huge currents going through them, and basically you've got lines of plasma (positive and negative ions -- which allow current flow) which accelerate together, making for the pinch effect.
This all happens very, very quickly, and at nice high temperatures (thus thermal energy also helps contribute to fusion effects), so that fusion is kept on the edge of possibility.
The pretty sparks in the pictures are produced when those capacitors discharge -- there's a "skin" effect on the oil, where its surface is next to the air. Those big sparkies, are, in effect, just the spark from a very large, very expensive finger approaching a very large, very expensive doorknob on a nice dry day, after the very large, very expensive feet have been scuffed over a shag carpet.
From the outside it looks to be a competition, and mutually exclusive at that. What are the possibilities of hybridizing these methods? Could all 5 approaches come together and cooperate towards solving this puzzle? I can even suggest a few new Fusion approaches of my own.
Fusion is generally considered clean compared to Fission, at least in direct by-products (your containment vessel is another matter due to high-energy neutron bombardment). Could we abandon the completely clean approach to get across the finish line, and then improve towards pure forms of Fusion? By this I mean Fusion-Fission hybrids similar to an H-Bomb, which uses the neutron burst (and heat and compression) from a fission reaction to trigger a fusion reaction. Would seeding our deuterium-tritium pellets with cores of plutonium, or other more unstable isotopes, yield better conversion ratios? Can micro critical masses be achieved by compression with fissionable products? How about micro fission generators, that rely on micro fission explosions. Then like our theoretically perfect fusion reactors, it would be impossible to go critical, because you would never have the fuel density to achieve run away fission (take away the compressive mechanism, no fission).
Anyway I'm just a lay person, but I figure there should be a few good Physicists in the forum, that could answer my core question about whether there a hybrid approaches being tired. I would be especially intrigued to learn if muon catalyzation has been tried with any of the other 4 approaches. For those unfamiliar with muon catalyzation, the essential idea is that an electron can be displaced by a muon for short periods of time, with a subsequent huge reduction in the size of the electron/muon orbital cloud, allowing atoms to come much closer together before mutual repulsion forces them apart. Thus a much lower thermal energy is needed for fusion -- hope I got that right :-)
Letter To Iran
Even if we leave aside the radioactivity of deuterium and tritium
Deuterium is stable. Tritium decays by emitting a low energy electron so if you're carrying a big chunk in your pocket it might sterlize you at worst. Rain water contains tritium so it's not like the world can't cope with it.
The main byproduct of nuclear fusion is helium-4 which hardly qualifies as radioactive waste.
:wq
From http://home.earthlink.net/~jimlux/nuc/reactions.h
Good luck getting your hands on tritium. Deuterium can be bought, or produced yourself with patience. Other reactions have very high threshold energies.
Note that this energy still isn't enough to penetrate the Coulomb barrier - it's the best tradeoff point between getting the particles close together and keeping them nearby long enough for there to be a reasonable chance of quantum tunnelling taking you through the barrier. So, most collisions will still just cause scattering.
Also note that any system involving a lot of scattering becomes Maxwellian (has a Maxwell-style temperature distribution). The fusor functions best in non-Maxwellian regimes. When the plasma thermalizes, it gets much colder due to the presence of cold ions (or cold, neutral molecules) from the source gas.
Evidently the problem with the better design is that once the fusion threshold was reached the temperature of the fusion plasma rose high enough to keep the ion injectors from being able to add new fuel to the plasma.
Farnsworth's better tube creates an almost ideal plasma:
As far as I know nobody has rebuilt the more complex fusor tube to try improving on the Farnsworth design. That design was brilliant. It is not obvious how the tube works until you realize that the virtual electrode produced by the electron cloud at the center of the tube is partially canceled by the ions injected into the center - which allows more electrons to concentrate in the virtual electrode - which allows more ions - etc. This allows a very dense plasma to be generated.
The truth is Farnsworth created more fusion in his desktop experiments than any of the giant, big money, fusion experiments since.
That was what surrounded the linear accelerator at my university. Parafin and other hydrocarbons also work. Basically, anything with lots of hydrogen atoms. Since a neutron is very close in mass to a proton, when a neutron hits a hydrogen atom you get a good chance of
H + n -> D
and deuterium is good and stable. Of course the D + n -> Tritium, which is radioactive, but can be dealt with reasonably easily.
Beta radiation, being charged, just needs some tinfoil. Gamma though needs lots and lots of concrete, or lead.
No, neutrons are easy to deal with, and anyway, my children find their extra limbs surprisingly useful.
Protoplasm. Quiet Protoplasm. I like quiet protoplasm.
It's not as simple as that. The temperatures and pressures needed to fuse helium into heavier elements is several magnitudes above what is needed to fuse hydrogen into helium. The energy expenditures needed would far outweigh the current cost of obtaining these elements.
A good way to research the topic of fusion is to look up information on the formation and life cycle of stars, nature's fusion reactors. You'll find that as very massive stars age, they burn through their hydrogen fuel quickly. Once that's all used up, gravity threatens to collapse them, until temperature and pressure in the core raises to the point that fusion into heavier elements can happen.
But then you'll see that the first steps of the heavier fusion processes create very common elements: carbon, oxygen, nitrogen. That's precisely why these elements are so abundant. By the time you get to elements even remotely rare, you're talking pressure and temps on astronomical scales. Finally, in the very massive stars, fusion can't go any further than iron, because after iron, fusion reactions no longer yield energy, but absorb energy. So after iron, it becomes an even more uphill battle.
Most likely if we do ever manage to harness fusion, it will stop at helium, as that will serve our needs well.
Karma: Frotzed (mostly due to the Frobozz Magic Karma Company)
As long as the helium released is made of stable isotopes, it will have little to no effect. The Earth has insufficient gravity to retain either hydrogen or helium in significant quantities. The helium will basically waft away into space. If helium could be retained in the atmosphere Earth would be a gas giant.
Not exactly the reason they use hydrogen. It is close in mass to the neutron so there is efficient transfer of energy to the hydrogen, which means the neutron slows down fastest in hydrogenated materials. So, the neutron "thermalizes" quickly in water, and it can be more readily absorbed by other things that have a higher reaction rate...like boron. And let me tell you, the neutrons coming from a fusion reaction aren't "easy" to deal with. They take a lot of slowing down before they get into an energy regime where they are easily absorbed. But, it can be done. Take it from me...I'm a nuclear physicist.