Incidentally, the difficulty in making antimatter is a major reason why the Large Hadron Collider collides protons against protons. Some previous colliders (e.g., Tevatron) have collided protons and anti-protons (which generally are “cleaner”, easier to analyze collisions), but you can’t get as many collisions that way (less luminosity) because you can’t make anti-protons as quickly.
One mole of antiprotons would take only 300 million years to make at the Fermilab antiproton source. (Of course, holding on to any of those antiprotons for any significant time (say, a month) is another story…)
If you want anti-atoms, then things get a lot harder. From last week: storage of a few antihydrogen atoms for 15 minutes.
Only $50M to double production rates? If so, you’ve got a deal.
Quoth These are my own pants:
I was considering giving that formula, but that’s not really right, either. The Space Shuttle is a rocket, and a rocket’s fuel consumption is dominated by massive inefficiencies. And just how massive those inefficiencies are depends in a complicated way on a lot of factors, like how many gees the payload is able to tolerate, how hot you can get the ejecta, and what the composition of the ejecta is. Just using the conservation of energy will get you an upper bound on the speed attainable, but it’s a very weak upper bound.
Yes indeed, thougzh as Washoe asked what would happen if all the energy of the Tsar Bomba was converted in to the kinetic energy of shuttle (okay he didn’t quite use that phrasology), so it’s the correct formula.
Yes, that’s what I really meant, despite the fact that my query was riddled with poorly phrased concepts. Basically, I was thinking “what could we do with all that nifty energy if it were applied to good use?” In my mind I was picturing a hypothetical reusable vehicle that could ferry workers to any point in the solar system in a matter of days or even hours, or maybe an interstellar probe. Obviously though, we would have to figure out how to fuse a small amount of hydrogen first.
P.S.—Thanks, pants—it was a somewhat bigger hint than I was fishing for, but you saved me a few hours of head scratching. Uh…did I get the right answer?
Minor nitpick, the [Teller–Ulam design](Teller–Ulam design) that most U.S. thermonuclear devices are based on has the fission device (primary) adjacent to the fusion fuel (secondary).
Honestly, why would anyone ever bother with an anti-matter weapon? We can already build a city-busting bomb small enough that several can be launched with a single ICBM. Moreover, these bombs are stable enough that they can be stored for years if properly maintained. We also have a range of chemical explosives, from fuel-air devices that can devestate city blocks to drone-fired missiles designed to take out small vehicles. These, too, can be stored safely and delivered in a number of exciting ways.
What useful function could an antimatter bomb serve?
If you could, a) produce a lot of antimatter relatively quickly, and b) produced a reliable containment vessel that doesn’t use too much power, there would be a lot of advantages.
No possible radioactive contamination. No radioactive wast when mining, producing or dismantling them. No fallout.
Much smaller warheads.
Perhaps far more practical to use as battlefield as well as strategic weapons.
And – cooler, scarier, and better at keeping aliens out of our face.
Because as a species we are astonishingly proficient at one thing: self-destruction. Anything we can do to further that noble endeavor is worth allocating at least a few billion in R&D funds towards.
Probably less; calculating from the figures shown in the table that I linked to in post 16, the combined output of the Nagasaki and Hiroshima bombs was equivalent to 754 milligrams of antimatter. A gram might be enough for several Shuttle launches. I’ll see if I can dig up exact figures.
Specifically, those losses are combustion or decay loss of the power source, thermal losses within the chamber, uncaptured thermal energy in the exhaust plume, and residual kinetic energy of the exhaust products. In traditional thermochemical rockets, those losses are 30-60%. The propulsive efficiency, η[sub]p[/sub] = (2u/c)/(1+(u/c)[sup]2[/sup])), with u being the velocity measured from the initial reference frame and c beign the effective rocket exhaust velocity.
For a chemical rocket, there is significant penalty in the expansion and thermal losses that limits just how efficient a rocket can be, either in theory or, as a practical measure, from the limits in material capability of the chamber and throat and loads acceptable by the payload as alluded by Chronos. A theoretical electron/positron antimattter rocket, which yields high energy photons (gamma ray wavelengths) as the products, could achieve a maximum theoretical upper bounds as the exhaust velocity is c, is actually c (the speed of light in a vacuum), although you have to make corrections at high relative speeds for redshift losses. (Proton/anti-proton rocket would see reaction losses in the form of neutrinos and unstable muons.)
However, the reality is that even if you could produce antimatter directly, you couldn’t control the direction in which it produces photons, and reflecting and directing high energy photons down the vehicle axis is far beyond conventional technology. More than likely, if we did have an economical source of antimatter, it would be more feasible to make use of it as an impulse source for conventional fusion, or as a muon source for muon-catalyzed fusion. However, if we have to make antimatter (rather than collect or mine it from some natural source) then the amount of energy we put into production will never be recouped in use.
Stranger
Would this change matters any?
http://rsta.royalsocietypublishing.org/content/368/1924/3671.full
This is the paper that HMHW liked to in his first post. Does the word ‘cold’ in this context imply the same sort of ‘free lunch’ scenario that it does that it does in the term ‘cold fusion’?
No, it means basically just the same sort of thing as it means in a ‘cold lunch’ scenario – antimatter that’s not very hot, i.e. is low energy (often, ‘cold’ and ‘hot’ is used in particle physics to refer to the kinetic energy of individual particles, even though we are in everyday contexts more used to thinking of those terms as being applicable to aggregate substances). Cold antimatter merely has the virtue of being more easy to capture, simply because it’s not going so fast; it’s somewhat less straightforward to produce than ‘hot’ antimatter, since the latter is what you typically get in high-energy particle collisions.
(Oh, and Pasta, I didn’t know Fermilab had that much of an advantage in antiproton production! I guess I’m already too used to give CERN the edge…)
CERN has the highest energies, which is a very useful thing, but it’s not the be-all, end-all of particle physics.
And I’m not at all confident that an antimatter weapon would be “clean” with regards to fallout. Annihilation reactions of hadrons are messy, and you get all kinds of particles thrown every which way, at high energies. I’m sure at least some of the things thrown off would be quite capable of transmuting ambient material into something radioactive. All the same processes that cause fallout in a hydrogen bomb would still apply, if anything more so. Now, it probably would still be cleaner per energy than a pure fission bomb, and certainly cleaner than something designed for fallout like a cobalt bomb, but “cleaner than a fission bomb” isn’t exactly resounding praise.
A one megaton thermonuclear bomb weighs hundreds of pounds and couldn’t be stored in anything smaller than a steamer trunk.
A one megaton antimatter warhead would weigh about an ounce (not counting the size of the containment vessel), and could theoretically be stored in a brief case.
Maybe it’s not the best choice for a government’s all-out war arsenal, but it makes a much better choice for a terrorist weapon.
We’ll keep an eye out for terrorists trying to procure equipment and land to construct a Tevatron-class particle accelerator. Fortunately, to date this has been the exclusive domain of major industrial countries, international consortiums of high energy physics researchers, and eccentric genius multi-billionaires with a guilt complex and a penchant for the dramatic, but you never know.
Stranger
And that’s a yotta power!
<minor tech edit nitpick>
You don’t need to capitalize the fully-written-out names of SI units. Only some of the symbols (mostly those derived from names) are capitalized. Thus: W, but watt. Pa, but pascal. N, but newton.
<returning you to discussion>
Interesting SDMB fact of the day!
I think your conception of fusion warheads is a little off- basically the fission primary is off to one side of the fusion secondary, not around it.
What happens is that when the primary goes off, there’s a containment vessel around the whole thing, that contains the explosion for a very short time, but long enough to start the secondary compression (which FYI, is caused by ablation from the surface of the secondary due to extreme heat, kind of like a inside-out rocket motor)
A very small matter/antimatter explosion could be used the same way, and with the substantial benefit of no fallout from fission.
The other thing that antimatter would be useful for without being a bomb in its own right would be as a boosting agent in regular old fission bombs. IIRC, matter/antimatter annihilation would be much more useful than the current tritium boosting as far as creating a burst of neutrons is concerned.
Matter/antimatter annihilation “at rest” is not a good way to make neutrons. In particular, proton+antiproton cannot yield any neutrons in the primary reaction. You will have a small secondary rate of neutron production as the outgoing pions, say, interact in the surrounding material and produce / kick out some neutrons from there, but those neutrons will typically be nowhere near the fissionable material.
This is what I’m talking about:
http://ffden-2.phys.uaf.edu/213.web.stuff/scott%20kircher/fissionfusion.html
I may have oversimplified too much; IANA physicist!
At the risk of provoking the slumbering beast, do you remember this chaotic thread? After it was firmly established (I think) that thermonuclear reactions do not convert matter to energy despite popular misconceptions to the contrary, somebody asked “well, what about antimatter?” The question fell through the cracks and went unanswered, but your post appears to indicate that the same thing holds true when antimatter meets matter—namely that the energy comes from the dissipation of the binding energy which was previously holding the stuff together. Is this true?