Published online 3 April 2007 | Nature | doi:10.1038/news070402-3

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Magnet failure could delay hunt for Higgs

Fermilab admits it is to blame for design fault.

A woven glass cloth holding some magnets in place isn't up to the job; all 9 magnet assemblies meant to focus the beam could be affected.A woven glass cloth holding some magnets in place isn't up to the job; all 9 magnet assemblies meant to focus the beam could be affected.

Construction of the world's most powerful particle collider has been hit by the sudden failure of a key part of the device.

The Large Hadron Collider (LHC), based at CERN, the European Laboratory for Particle Physics in Geneva, Switzerland, is due to start generating data in the summer of 2008. It will smash protons together in collisions that are expected to be energetic enough to identify the Higgs boson, the particle thought to endow all others with mass.

But that launch date is now in question. During a test on 27 March, part of the 'quadrupole' magnet system that will be used to focus the collider's proton beam ruptured. Personnel had been moved away from the area before the test and no one was hurt, but the incident means that the magnet involved will have to be redesigned.

Officials from Fermilab, the US particle physics lab that designed and built the magnet, said the explosion occurred during a simulation designed to assess how the magnet would respond to an increase in temperature beyond the normal range expected in the experiment.

Such an increase would cause the magnet to leave its superconductor state and develop electrical resistance. That would bump up the temperature more, causing the liquid helium surrounding the magnet to vaporize. The gas would then exert immense pressure on the magnet and surrounding structure — the test was designed to simulate this eventuality.

Unfortunately, the structure was not up to the job. When simulating the 20 atmospheres of pressure that the structure would experience, the magnet began to move around. The movement displaced and weakened a tube connecting neighbouring magnets, which then ruptured.

Loud bang

The noise was loud enough for safety officials to demand that those present have their hearing checked. All have since been given the all clear.

Fermilab staff say that the responsibility for the failure lies with them. Judy Jackson, the lab's director of communications, says that one of the structures that holds the magnet in place — made from a woven glass cloth named G11 — was not designed to the specifications required by the LHC.

Jackson adds that the documentation for the parts was reviewed four times without this error being spotted. "We're going to be asking how this happened," she says.

Construction of the LHC is complete; more than 1,200 magnets have been installed in the 12,500-tonne detector. This includes 392 quadrupole magnets that help to keep the beam on track. But the problem should be limited to, at the most, the nine specially designed quadrupole magnet assemblies provided by Fermilab to focus the beam.

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Fermilab's association director for accelerators, Stephen Holmes, is now heading up a team that is working with CERN scientists on a design change that may be able to be carried out without removing the magnets from the collider tunnel. The team plans to present a potential solution at a meeting at CERN on 24 April.

After that, Fermilab staff say they are unsure how long it will take to implement the changes. "But the goal is to get it done so it doesn't affect the start-up schedule," says Jackson. "We don't see anything that tells us we can't do that."

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