Monday, May 18, 2009

The Anti-Matter Bombs

Angels & Demons’ Antimatter Bombs - For Real?

Courtesy of Wired Blog NetWork

Dan Brown’s bestseller Angels & Demons hits the big screen today. For anyone who managed to miss the mega-bestseller, the plot hinges on a plot to blow up the Vatican using an antimatter bomb — a tiny device with the power of a nuclear warhead. They may sound good in a thriller, but are antimatter bombs more than just fiction?

In principle, antimatter looks like the ultimate explosive. Matter and anti-matter annihilate each other on contact, releasing energy according to Einstein’s famous formula. This tells us that one pound of antimatter is equivalent to around 19 megatons of TNT. So, in theory, you could make a pocket-sized bomb that would devastate a city. There is the slight issue of containment – the antimatter has to be kept in a complete vacuum and prevented from touching the walls of the container. But once you’ve solved that one you can go out and wreak havoc… just as soon as you’ve got your antimatter.

And there’s the big problem. In Angels & Demons, the antimatter is stolen from CERN, the European Nuclear Research Center. And it’s true - scientists there really have produced antimatter. But only in submicroscopic quantities. “If you add up all the antimatter we have made in more than 30 years of antimatter physics here at CERN, and if you were very generous, you might get 10 billionths of a gram,” CERN’s Rolf Landua, told New Scientist magazine recently. “Even if that exploded on your fingertip it would be no more dangerous than lighting a match.”

Their website makes it clear that a weapon is not on the cards. “It would take billions of years to produce enough antimatter for a bomb having the same destructiveness as ‘typical’ hydrogen bombs, of which there exist more than ten thousand already,” the site says. “The public somehow anticipates the antimatter bomb, but we have known for a long time that it cannot be realized in practice.”

CERN is dedicated to peaceful research. So it’s understandable that they would not want any of their work to be turned to military uses. But they may be downplaying, just a bit, the long-term potential for antimatter weapons.

The current means of manufacturing antimatter relies on firing a high-energy particle beam at a target (that’s one of the things they can do with their giant particle accelerators ). But there may be far more efficient ways of doing it. One NASA study recommends antimatter production via the spontaneous generation of particle-antiparticle pairs associated with vacuum fields. NASA’s interest stems from the fact that antimatter could be the ultimate rocket fuel. Rather than using pure antimatter – which they accept is always going to be too expensive – NASA have looked at Antimatter Initiated Microfusion, using a tiny amount of antimatter as the spark to set off a nuclear reaction. An AIM-powered spacecraft would require between one and a hundred micrograms of antimatter, depending on the mission.

This NASA study suggests that antimatter could be produced in that sort of quantity. The cost of antimatter is, by their estimates $62.5 million per microgram (…I like that “.5″). However, they suggest that a dedicated antimatter production facility, with a pricetag of $3 - $10 billion, would bring the price down to just $25,000 per microgram.

By my calculation, one microgram would be equal to around a hundred pounds of explosive, what might be termed a tactically useful quantity. (For example, the one-pound warhead the small Spike missile could be made several times more powerful than Hellfire twenty times the size, which might be useful for high-value targets.)

The Air Force’s “Revolutionary Technology” program showed some interest in this application, about five years back. A 2004 Broad Area Announcement expressed interest in several innovative technologies for munitions, including “Positron Energy Conversion and Advanced Energetics.” A positron is the antimatter equivalent of an electron, and perhaps the easiest anti-particle to manufacture and store.

When I asked about the Air Force’s antimatter work, they shied away from any mention of weapons: ” This technology could be used for a number of applications such as a new propulsion system, ultra-lightweight satellite power supplies, high specific impulse engines, and precision measurements - though these applications may be far into the future, as much as 30 years or
more,” a spokesman told me.

Positrons can be stored in a Penning Trap, a sort of magnetic bottle. (The Air Force bought a new positron trap in December — but only for a device to examine defects in semiconductors.) However, such traps are leaky and you can’t store your positrons indefinitely. There’s also the issue of what happens when the power fails. The trap stops working and all your positrons come into contact with the container walls: boom. Then there’s the question of how many positrons you can store. At the moment storing a microgram of positrons would require a Penning Trap of stupendous size. A 2004 report by the National Research Council said that much greater energy densities were needed for positrons to be useful as an explosive. The study advised against heavy investment in such a high-risk, immature technology.

But of course, that was before Angels & Demons became popular. Soon everyone will be aware of destructive potential of a quarter gram of antimatter. After seeing the movie, you just know there will be some Pentagon chiefs and politicians saying, “This antimatter bomb looks great, where do we get one?”

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