Plans for the Large Hadron Collider (LHC) to start smashing its first particles next week have been derailed after it developed a significant fault yesterday.

The problem with several of the £3.6 billion accelerator’s super-conducting magnets means it will be impossible to stage its first trial collisions next week, and further delays could follow once the damage has been fully assessed.

While a faulty transformer that had hindered progress for much of the past week has now been replaced, as first reported by The Times, the magnet failure is potentially more serious. It could even take several weeks to resolve, depending on the extent of the damage.

The incident was what is known as a “quench”, in which the temperature of superconducting magnets that are normally chilled to 1.9C above absolute zero started to rise.

It caused the temperature of many of the 200 or so magnets in the affected sector to soar by as much as 100C, which would normally take about two weeks to be cooled again.

There could be further delays because helium has also escaped into the LHC’s tunnel, and there were unconfirmed reports that the vacuum had been lost in part of the beam pipe in which protons circulate.

Engineers were still investigating the extent of the malfunction this afternoon, and CERN officials could not say how long it would take to fix and what impact it would have on the LHC’s schedule. The fault does not pose any longer-term threat to the LHC.

James Gillies, head of communications at CERN, said: “The incident occurred while we were commissioning the final sector, and a lot of helium has leaked into the tunnel. We are investigating now, and we should have a clearer picture over the weekend.

“How long it takes to resolve depends on what it is. It could be very little time, or it could be many weeks. I don’t want to speculate until we have more information. It certainly means we will not have collisions on Monday, or indeed next week.”

The quench took place this morning, just a day after the LHC’s beam was restored following the earlier transformer failure. It occurred during the final test of the last of the LHC’s electrical circuits to be commissioned, so it can handle the enormous current required for magnets to bend protons at unprecedented energies.

At 11:27 local time (10.27 BST), the LHC’s online logbook stated that helium had been lost to the LHC tunnel and that vacuum conditions had also been lost. It added that the CERN fire brigade had been called to the scene, but the entry has since been removed.

Helium is not a fire hazard, but it could present a risk to anybody in the tunnel as it displaces oxygen. Nobody was endangered by the incident, because no-one is allowed into the LHC’s tunnels and detector caverns while the machine is operational.

A CERN source who had initially feared that the incident could delay the LHC’s operations by several weeks said hopes were rising during the afternoon that the damage was limited. “They just managed to bring back the compressors again, so who knows,” the source said. “These guys make miracles and could bring back the system in a week.”

The LHC’s network of magnets, which will eventually fire protons around the 17-mile (27km) ring at 99.9999991 per cent of the speed of light, are chilled to 1.9C above absolute zero, so that current flows through their coils without resistance. This superconductivity allows the magnets to generate much stronger fields than would otherwise be possible.

A quench occurs when these magnets warm up and lose their superconducting properties. The online logbook entry described the incident as a “massive quench” in sector 3-4 of the LHC, while lies between the Alice and CMS detectors.

After last week’s flying start to the LHC operation, when the first beams were sent around the 17-mile (27km) ring much more quickly than had been predicted, the team had been hopeful of staging its first trial collisions this week.

Those plans had to be shelved, however, when the beam was lost for several days because of the transformer failure, which interrupted power to the superconducting magnets serving one of the accelerator ring's eight sectors.

The transformer was replaced on Wednesday, and the beam was restored on Thursday.

When the machine is ready to make its first collisions, these will involve beams with an energy of 0.45 teraelectronvolts (TeV), which previous accelerators have been capable of reaching since the 1980s. The aim is to check that the detectors are working properly, and the collisions will not be used for scientific experiments.

The next goal will be to produce beams with energies of 5TeV, which would smash the 1TeV world record, held by the US Tevatron in Illinois. This is scheduled to happen by October 12, in time for the LHC’s formal inauguration ceremony on October 21.

Over the winter the LHC will be shut down for further further fine-tuning. Next year it will be boosted to its maximum energy of 7 TeV to produce results that should shed light on some of the most important and enduring questions in physics.

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