Toiling in the fields of physics
Posted: Thursday, June 21, 2007 7:10 PM by Alan Boyle
Colin Hicks / MSNBC.com |
A worker on a crane checks one of the segments of the Compact Muon Solenoid, a
particle detector that will be part of CERN's Large Hadron Collider.
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The huge warehouse seems out of place in the French countryside, surrounded by pastures and cornfields. And if the farmers who work those fields were to take a look inside the structure, they might be forgiven if they thought space aliens had dropped a flying-saucer factory in their midst. Sticking up from the warehouse floor are massive disks of metal, lined up in a row and rising more than four stories into the air.
These are pieces of the Compact Muon Solenoid, one of the four major detectors being built for the world's most powerful particle collider. Right now, the rounds look as if they were cut from a giant metallic jelly roll, measuring 50 feet (15 meters) in diameter. But when all those slices are lowered through a hole in the warehouse floor and assembled, sometime in the next few months, the Compact Muon Solenoid will be a 13,750-ton (12,500-metric-ton) cylinder sitting in the guts of CERN's Large Hadron Collider, 330 feet (100 meters) beneath the countryside.
"It is the heaviest scientific experiment ever," said Steven Nahn, a physicist from the Massachusetts Institute of Technology who is a member of the CMS research team.
To call this contraption "compact" seems like a gross misnomer: The CMS is compact only in relation to its rival sibling, the ATLAS detector, which is roughly twice as large but only half as massive. The contrasts in the weights and dimensions hint at the different designs for ATLAS and CMS - two detectors that are designed to probe the same types of subatomic mysteries.
When the collider is turned on next spring, the teams behind ATLAS and CMS will be racing each other to find evidence of long-predicted but still-unseen subatomic particles, such as the Higgs boson (thought to give rise to mass itself) and supersymmetric particles (which may contribute to our universe's mysterious dark matter). If one detector finds a new twist in physics, the other will serve as a reality check.
As we toured the CMS site today, Nahn noted that the competition is a friendly one. Both teams recognize they need each other - particularly when it comes to stalking the Higgs boson. "If one finds it, the other better see it," he told me.
Construction crews check each slice of the detector, lower it down into the collider cavern with a giant crane, then outfit it for the work ahead. Eventually, all the slices will be smooshed together, surrounding a solenoid that Nahn calls "the world's biggest doorbell magnet." Within that high-powered solenoid magnet will be an intricate silicon device, designed to follow the tracks of subatomic particles that are thrown off by the collision of high-energy proton beams.
Data will flow in floods from the CMS detector. "People describe it as an 80-million-pixel camera that takes 40 million frames per second," Nahn said. Computers will have to winnow that raw data down to mere millions of bits per second - separating the wheat from the chaff. That should be something the farmers working above the CMS totally understand.
Colin Hicks / MSNBC.com |
Fermilab's Peter Limon, MSNBC.com's Alan Boyle and MIT's Steven Nahn walk down
the ring tunnel for CERN's Large Hadron Collider, 330 feet below ground.
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Before all those bits start flowing, the collider's 17-mile-round (27-kilometer-round) underground ring will have to be ready to handle the accelerated proton beams - and that's the job of people such as Fermilab's Peter Limon, who is working on the U.S.-built segments of the ring's powerful magnets.
As our group headed toward the elevator to descend to the ring tunnel, Limon checked our hardhats and handed us metal containers that looked like industrial-strength lunch boxes with canvas straps attached. He explained that the boxes actually contained emergency breathing equipment, in case something went wrong in the tunnel's ventilation system. It's a safety requirement, but Limon said he's never had occasion to use the equipment.
"My advice is, if anything happens, drop that thing and run to the nearest exit," he told us.
Despite his easy-going manner, Limon knows all too well that bad things can happen underground. In March, his efforts suffered a huge setback when a magnet segment broke during a high-pressure test. The segments look like sections of pipeline on the outside, but on the inside they're stuffed with plumbing, cryogenically cooled vacuum chambers and beamline conduits. It turned out that a particular type of segment was improperly designed to handle the pressurization. When the lines were put to the test, the magnet's innards pushed out in an unexpected direction and buckled with a loud bang.
"It's an embarrassment, it's a pain," Limon told us down in the tunnel.
Now that the problem has been analyzed fully, all the magnets with the design flaw are being fixed. "The important thing is that all the fixes can be done in situ," Limon said. Modifying the magnets in place, rather than pulling them up out of the tunnel, will save a lot of time. Nevertheless, the mishap put a huge dent in the schedule for getting the Large Hadron Collider up and running.
Jos Engelen, CERN's chief scientific officer and deputy director-general, confirmed that the scheduled start of operations is being pushed back from November to next spring, in the May-June time frame. But he also told me the project's coordinators would try to make up for some of the lost time by doing some of the commissioning activities in parallel, and by bringing the collider up to full power more quickly once everything is ready to go.
"Around Christmas of 2008, we should be satisfied, with a good harvest of entirely new data," Engelen said.
Engelen was also pleased to report that CERN's Council approved a plan to provide $193 million (240 million Swiss francs) over four years to upgrade the Large Hadron Collider and "optimize its performance." The money will come from increased contributions by CERN's member nations, he said.
Like good farmers, Engelen and his colleagues are bearing the highs and lows patiently, confident that the scientific seeds they're planting underground will yield a rich bounty.
"You should be here when we switch on," he told me, "and only then will people realize how big a relief and how big a step this is."
Previously from the Big Science Tour: The science behind the tour ... Living in the Web's cradle ... Inside the big-bang machine.
