The inner triplets were installed in the LHC tunnel in 2006

The giant underground laboratory on the French-Swiss border is designed to probe the limits of physics.

It is the world's biggest facility of its type, and will collide sub-atomic particles in a 27km-long ringed tunnel.

One of eight magnet assemblies placed at points around the LHC failed in a test ahead of the lab's scheduled start-up in late 2007.

The magnet assemblies, called "inner triplets", consist of three "quadrupole" magnets that are cooled using superfluid helium at 1.9 Kelvin (-271C) inside a vacuum vessel.

One inner triplet is located on either side of the four major detector experiments at the LHC.

The magnets focus particle beams prior to collision at each of these four interaction points around the accelerator ring.

A statement from Fermilab, which built the inner triplet magnet assemblies, said that a structure holding the magnets in place broke during the test.

Understanding the problem

"Fermilab and Cern engineers are looking into this very closely," a spokesman for Cern told BBC News.

The spokesman said it was still unknown whether the failure would affect the schedule for the switch-on of the LHC.

"We're not saying the schedule is delayed or otherwise. We just need to understand the problem a bit better before we can say," he explained.

The issue is thought to be a "systematic" one affecting all eight inner triplet assemblies.

The structure broke as it was put under a pressure of 20 atmospheres and uneven forces were applied to it. Such forces are expected to occasionally occur during the operation of the LHC.

The LHC is a powerful and complicated machine, which will smash particles together at super-fast speeds in a bid to unlock the secrets of the Universe.

Over 1,000 powerful "dipole" magnets occupy the subterranean tunnel in which the accelerator is housed.

These magnets carry two beams of particles around the ring at speeds close to the speed of light.

One pair of inner triplets focuses these beams prior to collision at each of four experiments located around the LHC tunnel. The one affected in the test is located on one side of the Compact Muon Solenoid (CMS) experiment.

The CMS, along with the rival experiment Atlas, will seek to identify the elusive Higgs boson (known as the "God particle" because of its importance to the Standard Model of particle interactions), look for so-called supersymmetric particles and seek out the existence of extra dimensions.

These experiments, each about the size of a mansion, will capture and measure new particles produced in the beam collisions.