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Broken Magnet Highlights Largest Collider's Engineering Challenges

Mason Inman
for National Geographic News
Updated June 6, 2007
 
Editor's note: The original April 13, 2007, story has been updated to reflect the official decision to delay the initial "test drive" of the Large Hadron Collider due to technical glitches.

Even at the world's soon-to-be largest particle accelerator—a device that promises to push the boundaries of physics—scientists need to be mindful of one of the most fundamental laws in the universe: Murphy's Law.

In late March, a scant few months before the much anticipated Large Hadron Collider (LHC) was slated to go online, a small but crucial part of the machine broke with a bang.

The accident happened as a team was testing a set of magnets that will steer protons—tiny positively charged particles found in every atom's nucleus—around the accelerator to nearly the speed of light.

The test was meant to simulate what could happen in emergency situations, when gas might build up to high pressures inside the accelerator.

When the pressure inside got high, it snapped supports holding the magnets, and gas burst out of the tube, stirring up a cloud of dust. No one was hurt, but the dramatic failure revealed a design flaw in the massive machine.

"We were busy solving hard problems, and somehow an easy one slipped past us," said Jim Strait of the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois.

Fermilab was responsible for the part that failed in the tests, and they're now scrambling to work out a solution and put it in place as quickly as possible.

The accident—along with a handful of other technical glitches—will delay the initial "test drive" of the full accelerator but hopefully not its scheduled startup in 2008.

"We now intend to make the tests, which will allow the technicians to drive the machine, in late April or early May [next year] and then to go into full startup as planned by next summer," James Gillies, a project spokesperson, told the Reuters news service.

High Energy, High Speed

Still, scientists are thankful that they caught the problem before the machine actually powered up.

"If you don't do enough tests, you get something like the Hubble," said Dan Green of Fermilab, who also works on the LHC.

NASA's Hubble Space Telescope turned out to have a faulty lens due to a simple error. The gaffe wasn't caught until the telescope was in orbit, and it cost tens of millions of U.S. dollars to fix.

In comparison, the LHC's flaw was a relatively minor hiccup, but one that highlights the feats of engineering involved in solving some of science's greatest quandaries.

The LHC is a huge international collaboration among thousands of physicists from dozens of countries.

The accelerator will be housed at the European Organization for Nuclear Research, or CERN, which is based in Geneva, Switzerland.

Its 17-mile-long (27-kilometer-long) circular tunnel is drilled through the dirt and rock 165 to 575 feet (50 to 175 meters) below ground, crossing the French-Swiss border.

Two beams of protons, one going around the loop clockwise, the other counterclockwise, will move through the loop in a vacuum guided by a variety of magnets, including 1,232 superconducting dipoles.

To keep cool while holding intense electrical current, the dipoles sit in a bath of superfluid helium, a special type of liquid helium that is unusually efficient at transferring heat. The helium is kept at 1.9 Kelvin, or -456 degrees Fahrenheit.

Careful testing of all components is a must, as the LHC will be the first particle accelerator that could destroy itself if its proton beams went out of control.

Each high-speed beam has as much energy as a train going about 90 miles (150 kilometers) an hour. But all this energy is packed into a stream that's less than a hair's breadth across.

"The stored energy in the beam is enormous," Fermilab's Strait said. "You have to treat it with great respect."

When the two proton beams collide, they release much of that energy.

In keeping with Einstein's equation E=mc2, which describes how energy can turn into mass, this energy can transform back into new particles that are often much heavier than the protons they came from.

It's analogous to driving two Honda Civics at high speed into a head-on collision, and when they hit, out pops a never-before-seen luxury SUV.

Collision Reconstructions

But the new, heavy particles coming out of the collisions rarely last long. The most exotic particles live for only fractions of a second before decaying, producing a mess of more humdrum particles.

"You typically get showers of tens or hundreds of particles," said Peter Jenni of CERN.

To figure out which types of new particles were created, physicists will have to sort through the debris from each collision. Like police investigating a crash, they try to reconstruct what happened.

That's where the accelerator's four main detectors come into play.

ATLAS, the largest detector, sits in a huge underground cavern nearly the length of a football field and several stories high.

The barrel-shaped detector—weighing more than 7,700 tons (7,000 metric tons), nearly as much as the Eiffel Tower—surrounds the tube where the proton beams will collide.

(See a photo of the world's largest superconducting magnet, which is part of ATLAS.)

The debris from the collisions will fly through the detector, which is about 150 feet (46 meters) long and 75 feet (24 meters) across.

"Its size and complexity certainly puts it in a new generation" of detectors, about ten times bigger than those made before, Jenni said.

The detector will tell physicists how fast the particles are going, how much they weigh, and other properties.

ATLAS's first goal is to look for a long-sought particle called the Higgs boson, which may explain how objects get their mass.

The ALICE, CMS, and LHC-B detectors will also look at various aspects of particle collisions to solve other physics mysteries, including how many dimensions of space really exist and what the universe was like in its earliest moments.

Meanwhile, physicists are already planning for the next big particle smasher, the International Linear Collider, which will explore collisions between electrons and their positively charged counterparts, positrons.

Will the particle detectors for that machine be even bigger and more complex?

Green, of Fermilab, said: "Well, they won't get simpler."

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