How do you create and use antimatter?

[Line]

Just how hard is it and how do you create antimatter?


I'm thinking if we could use it to start nuclear explosions. How much antimatter does it take to make a fusion reaction occur? Could you use antimatter to create matter? Once a certain amount of antimatter is created could you then use that antimatter to genreate enough energy to create tons more antimatter?

 

[Danger]

Hi again, Line. Arildno and Zapper are probably the guys who can answer the first part of that question most accurately. They're the working particle physicists.
Antimatter/matter annihilation is not by any means a 'nuclear' explosion; it makes a nuclear explosion look like a firecracker in comparison. In an A-bomb (fission) explosion, something like 0.01% of the mass is converted to energy. An H-bomb (fusion) reaction releases about 0.1%. Antimatter is 100%. One half gram of antimatter combining with one half gram of matter let's loose with something on the order of 25,000,000 kilowattt-hours of energy. That is primarily gamma radiation, but there's still one hell of a huge KABOOM factor. To put it in rough perspective, the bomb that levelled Hiroshima could have fit in the filter of a cigarette if it had been antimatter instead of U-235.
And no reaction of any kind is ever going to produce enough energy to re-establish itself. That would be a perpetual-motion device, in violation of the 2nd law.
Lastly, forget about creating 'tons' of antimatter with any current technology. The best accelerators on the planet are producing it in micrograms.
I'm out of my depth here, so I'm backing off in deference to the pros.

 

[Line]

I'm saying since it only takes a small amount, a spec of it could probrably ignie hydrogen to the fusion point.

Also I'm not saying reuse the antimatter. I've heard creating antimater takes huge amounts of energy. SO wouldn't it be easy to use antimatter, create huge amounts of energy and create even more antimatter with hjat energy?

 

[Danger]

Okay, I see what you mean. Yes, you could replace the A-bomb trigger for a fusion device with an antimatter detonation.
Your second assumption is also correct, but in a limited way. There would still need to be an external energy source. What you propose is equatable to burning petroleum products in order to power a refinery. It works as long as there's petroleum coming in from somewhere; if not, you end up with a diminishing spiral of material that eventually is exhausted. Perhaps an even more apt comparison would be using the power from a hydroelectric generator to pump the water back up to the top. It'll work to some extent, but there'll always be a net loss until there's nothing left to pump with. Ie: you can never pump as much up as came down in the first place.

 

[CPL.Luke]

Line it takes a certain amount of energy to create the antimatter, when you cause the antimatter to annihalate and release the energy you get back less energy than you put in. So you could reuse the energy and make some more antimatter but you'd make less than you made oriiginaly

 

[Line]

So if even antimatter isnt' enough to make more how on Earth do they make it?

 

[franznietzsche]

So if even antimatter isnt' enough to make more how on Earth do they make it?

With far more nuclear, hydro, and coal power than you want to think about. I believe the electricity bill for LANSCE (a linac) is close to $1,000,000 per month, IIRC.

 

[Mk]

If you want to get past break-even, you're going to have to find the resource to use, not create it. Sometime in the future if we're doing interstellar travel we may find a space with a lot of antimatter in it, that we could use for fuel, but if we're having to create it, we are only losing energy.

 

[WhyIsItSo]

If you want to get past break-even, you're going to have to find the resource to use, not create it. Sometime in the future if we're doing interstellar travel we may find a space with a lot of antimatter in it, that we could use for fuel, but if we're having to create it, we are only losing energy.

The only good reason I can think of to create it is for it's compactness. Getting a little sci fi-ish here, but if this becomes a viable fuel for space travel, you get a lot of energy per volume of fuel.

Engage!

 

[LURCH]

If you want to get past break-even, you're going to have to find the resource to use, not create it. Sometime in the future if we're doing interstellar travel we may find a space with a lot of antimatter in it, that we could use for fuel, but if we're having to create it, we are only losing energy.

I remember reading a report about a year ago (I think) about a solar flair which had produced over a pound of antimatter. If we could find a way to predict these events accuratelt and sequester tha antimatter before it reacts with the normal matter around it, that could be a way to "harvest" rather than trying to produce.

Regarding the OP, if the statement was true;

To put it in rough perspective, the bomb that levelled Hiroshima could have fit in the filter of a cigarette if it had been antimatter instead of U-235.

then a pellet of antimatter the size of a cigerette filter should be adequate to trigger a fusion reaction (since atomic devices are used as triggers for thermonuclear devices). Just an educated guess, but it should put us in the balpark.

 

[Line]

If only could find a way to create it , we'd have our nuclear problems solved.

 

[Chronos]

Creating anti-matter in the laboratory is extremely inefficient and, for reasons already noted [the 2nd law thing] takes considerably more energy than you can recover from the output. An even bigger headache is storing the stuff for later use which involves creating a 'magnetic bottle' - a very difficult feat. CERN is currently attempting to collect usable quantities of anti-matter via the ATHENA project. For details see:

http://athena.web.cern.ch/athena/

For an example of possible future applications, see:

http://arxiv.org/abs/astro-ph/0410511
Controlled Antihydrogen Propulsion for NASA's Future in Very Deep Space

 

[Line]

Now these magnetic bottels...are they storing antimatter in a gaseous state? I can't imagine a magnet storing something solid or even liquid.

 

[Danger]

Line, magnetic confinement is usually applied to individual particles of the same charge or plasmas. Both are electrically active. The Athena project that Chronos linked to collects the positrons and antiprotons separately in Pennington traps. I'm not quite sure what they do with the antihydrogen atoms once the particles are combined, and I don't really have time to dig into it right now. That's a really great link (thanks, Chronos!) that you should read in its entirety.

 

[SF]

I recommend the book: The Physics of Star Trek by Lawrence M. Krauss for an accurate description of the antimatter creating process and how a spacecraft powered by matter/antimatter collisions would function.

Or maybe it was "Beyond Star Trek"? :hmm:

Anyway, with the current methods of producing antimatter, it's an unfeasable concept.

 

[Danger]

Hi, SF. While a 'warp' engine is currently not something you can go build in your garage, antimatter production at this point is just about up to the demands of the 'ion-compressed antimatter/nuclear' project. It requires only a few milligrams. See the Marshall Space Flight Center website for details.

 

[Astronuc]

Fission of a nucleus of U-235 produces ~205 MeV (less than 1 MeV per nucleon). Fusion of a deuteron (H-2 nucleus) and triton (H-3 nucleus) produces 17.6 MeV or about 3.52 MeV per nucleon. One of the most energetic fusion reactions, D + Li-6 -> He 4, releases 22.4 MeV (per reaction), but that is only 2.8 MeV per nucleon.

In fission and fusion, the much of the energy released in the reaction is transformed into kinetic energy of the products - which means high temperature. This 'thermal' energy can then be transformed by a machine, e.g. turbine into mechanical energy to drive an electrical generator, which in turn produces a variable magnetic field, which in turn produces 'electricity'. The process thermal to mechanical energy conversion, usually involving the Rankine steam cycle, is quite inefficient. A Brayton cycle might achieve slightly higher efficiency depending upon the temperature difference between hot reservoir and cold reservoir.

Anyway, as for anti-matter, to create an antiproton, one needs to input an energy of at least 938.272 MeV, the rest mass of a proton/anti-proton, so that is 938.272 MeV per nucleon. Now the creation of an anti-particle must observe certain conservation laws, so by the typical method of anti-proton production (viz proton-proton collision), a proton is also created, so the initial colliding pair of protons must have in input of kinetic energy of at least 1.876 GeV or still 938.3 MeV/proton. However, collisions of protons are very difficult, and they rarely line up just right for a head on collision, and most of the time, the protons just scatter without a reaction, so one has to put more energy into the colliding protons to increase the probability that a glancing collision will exceed the threshold for the reaction which produces a proton/anti-proton pair. IIRC, one typically inputs 4-6 GeV per colliding pair of protons, and even then if one would get one anti-proton for 1000 proton-proton collisions, that is 4-6 TeV spent for one anti-proton. Then one can calulate how much energy it would take to create a gram of anti-protons. (Don't forget the positron production)

Fusion suffers from a similar problem in that the nuclei must have sufficient kinetic energy to overcome the Coulombic repulsion, and even then the nuclei are more likely to scatter than react. The kinetic energy, usually several keV to 200 keV means high temperature (1 ev = 11605 K, or 1 keV = 11605000 K), which means the atoms (light atoms) are ionized. A consequence of the ionization means that the electrons are also heated, and when the plasma is isolated/confined by a magnetic field, the electrons radiate a lot of energy as cyclotron and brehmsstrahlung radiation. Another consequence of the high temperature is high pressure, which is a function of particle density and temperature. Since there are practical limits on magnetic field strength and material strength (limits on human technology), there are practical limits on plasma densities (e.g. ~10¹⁴ particles/cc as compared to a typical gas at STP, ~10¹⁹ atoms or molecules/cc, and solids ~10²² atoms/cc) which we can create on earth. Stars are not so encumbered.

In a star, the intense EM fields, well beyond what we create on earth, with the possible exception of the few microseconds following the initiation of a fission (nuclear) or fusion (thermonuclear) bomb, can create very high energies in the multi-GeV range, and so anti-matter production is possible, but the anti-protons would not survive very long. High energy protons in the solar wind or galactic cosmic radiation cause the prodcution of antiparticles in the upper atmosphere. That is the source of pions and muons (pion decay) that scientists like Wilson detected back in the early 1900's.

Bottom line - anti-matter is difficult and very expensive for humans to produce.