Inside the antimatter factory
Posted: Friday, June 22, 2007 4:44 PM by Alan Boyle
Colin Hicks / MSNBC.com |
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Professor Joel Fajans of the University of California at
Berkeley, a member of the ALPHA antimatter
research team, looks over equipment at the
Antiproton Decelerator facility on the CERN campus.
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It's not often that a scientific experiment gets written up as a front-page news story, as well as a science-fiction twist in a best-selling thriller and a can't-miss movie script - but that's what's been happening to CERN's Antiproton Decelerator facility, the only place in the world where whole atoms of antimatter are built.
This summer, physicists at the facility are engaged in their own real-life thriller: Two teams of researchers are racing each other to be the first to trap atoms of antihydrogen in a magnetic cage. The researchers who do it first will grab the headlines once again. And the other team? "Being second is last in this game," said Jeffrey Hangst, a physicist at the University of Aarhus who is the spokesman for the ALPHA antimatter collaboration.
The race illustrates how competition kicks the science up a notch - and how hard it is to turn science fiction into science fact.
Today, Hangst showed us around the Antiproton Decelerator's digs, down one of the less-traveled streets on CERN's campus straddling the French-Swiss border.
"This is the hall mentioned in the Dan Brown book 'Angels and Demons,'" Hangst told us. "This is what inspired the book."
The first scenes in "Angels and Demons" - the book Brown wrote before "The Da Vinci Code" - focus on crimes of catastrophic proportions at CERN. An international conspiracy steals a quarter of a gram of antimatter, intending to use it to blow up the Vatican. And from there, Brown's protagonists and villains are off and running.
In the wake of the splash over "The Da Vinci Code," Hollywood is doing up a movie version of "Angels and Demons," with Tom Hanks returning to his "Da Vinci" starring role.
Of course, there's far less than a quarter of a gram of real-life science in the antimatter plot. (And despite what it says in the book, there's no evidence that CERN has a supersonic jet or an indoor skydiving facility, either.) So Hangst is pretty sure the world is safe from an antimatter Armageddon.
"To make a milligram of antihydrogen would take more than the age of the universe," he told me. "It's just not a useful weapons technology by any stretch of the imagination."
I guess that also means we won't be seeing a "Star Trek" matter-antimatter drive anytime soon.
Even if you set aside the science fiction, the reality at the Antiproton Decelerator is dramatic enough: Back in 2002, Hangst coordinated the ATHENA collaboration, which assembled antiprotons and positrons to create antihydrogen atoms. The achievement earned acclaim from scientific journals as well as the popular press.
ATHENA's rival, the Harvard-led ATRAP collaboration, accomplished the same feat using different equipment months later - and published its own set of scientific papers. The acclaim, however, was somewhat less.
Now ALPHA, the successor to ATHENA, is once again in competition with ATRAP. The funny thing is that the two teams both use the same Antiproton Decelerator, setting up shop in nearby sections of the laboratory floor. "The only two experiments that can do this are 5 meters apart," Hangst noted.
Colin Hicks / MSNBC.com |
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A yellow radiation sticker is pasted on the
lead-shielded box where positrons are
kept for the ALPHA antimatter experiment.
The antimatter trap itself is farther back,
in a welter of cryogenic plumbing.
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ALPHA and ATRAP have divvied up access to the facility with the Japanese-European ASACUSA collaboration, which is conducting a totally different type of antimatter research. Each of the three teams gets a daily eight-hour shift, which means the Antiproton Decelerator can be in a 24-hour usage mode.
This week, we've been talking mostly about CERN's Large Hadron Collider, which will become the world's biggest particle collider when it starts up next year. The Antiproton Decelerator is a very different part of CERN's research portfolio. The LHC will be focused on revving particles up to bust things apart at high energy, but the AD specializes in slowing antiparticles down so that they can be put together at low energy. The LHC involves thousands of researchers. In contrast, mere dozens are working on antimatter research.
ALPHA and ATRAP get their antiprotons from the same source, a ring tunnel in which negatively charged antiprotons are filtered out and cooled down to become manageable pulses of particles (hence the term "decelerator").
Although the two teams use different equipment and procedures, they follow a similar recipe to make antihydrogen. The antiprotons have to be slowed down and chilled down even further, to the point that they're just sitting in one section of a receptacle. Positively charged antielectrons (that is, positrons) are chilled down in another section.
The physicists working at CERN came up with clever electromagnetic traps to keep all those particles contained - almost like a Roach Motel for antimatter. "You can get in, but you can't get out," Hangst joked.
The next step was to blend the two ingredients carefully so that some of the positrons start dancing around the cold antiprotons, becoming atoms of antihydrogen. That's basically the state of the art up to now.
So far, physicists haven't been able to keep the neutral anti-atoms from drifting out of their electromagnetic cages - which means they quickly come in contact with ordinary matter and blow up. The only way to tell that anti-atoms were created in the first place is to detect the tiny, characteristic bursts of energy when they go away.
"Our critics will tell you that we haven't done any physics yet, and in some ways they're right, because we have yet to really measure something about antihydrogen, something fundamental about it," Hangst said. "Obviously if you want to do that, having the atoms disappear as soon as you make them is not a good idea. So the next step is to try to stop that from happening."
The challenge for ALPHA as well as ATRAP is to develop another type of cage that will still allow the mixing of antiparticles, but keep the resulting atom from drifting away. The two teams have designed different magnet systems that could theoretically "steer" the anti-atoms into a stable position.
Which system will do the trick first? "As usual, it's a race here - it's a race hour to hour," Hangst said.
Being able to keep antihydrogen in a cage is just one more step in a grander endeavor. Once physicists start storing up those anti-atoms, the next step would be to find ways to study them - in ALPHA's case, by using laser light to analyze the spectral signature of antihydrogen.
The conventional assumption has been that antihydrogen's signature would be identical to hydrogen's. But in recent years, scientists have found slight asymmetry between matter and antimatter. A close inspection of stable antihydrogen could help explain that asymmetry - and perhaps explain why there is almost no antimatter out there in the cosmos, even though theory dictates that matter and antimatter were made in equal proportions when the universe was born.
The antimatter factory at CERN could eventually blaze a whole new trail for physics, but for now, Hangst is focusing on the road in front of his feet - and the prize that's waiting at the finish line.
"When something like this comes out, you see it in newspapers all over the world," he said. "It's a big deal. ... It's not like anything I've ever been through before. And that's the atmosphere here."
CERN update: We reported Thursday that CERN was setting next May as the new target for the start of operations at the Large Hadron Collider, and today CERN issued the official news release mentioning May as the current goal. That time frame is in line with what was expected in the wake of a magnet mishap this March. Of course, the schedule could change again between now and next May, depending on how quickly the final phase of construction is completed. CERN's chief scientific officer, Jos Engelen, provided some extra wiggle room by referring to the beginning of June as well as May.
The release also refers to the additional financial support for upgrades at the Large Hadron Collider - yet another angle we reported Thursday.
Previously from the Big Science Tour: The science behind the tour ... Living in the Web's cradle ... Inside the big-bang machine ... Toiling in the fields of physics.
