LHC high-energy experiment held up by glitches

Two technical glitches have upset Cern's plans to discover new physics by smashing beams of protons into each other at 7 TeV on Tuesday morning
Written by Tom Espiner, Contributor

Initial attempts to get the Large Hadron Collider powered up to collide beams at their highest energy ever have been temporarily stopped by two glitches.

On Tuesday morning, Cern began ramping up energy in the Large Hadron Collider (LHC) to circulate two beams of protons, each with an intensity of 3.5 tera-electron volts (TeV), that it plans to smash together in a 7 TeV collision.

Cern physicists hope that the high-energy experiment will allow them to gain insights into fundamental physics, such as verifying the existence of the Higgs boson, a hypothetical elementary particle. The organisation is billing the event as the 'first physics' to come out of the LHC, which is the world's largest particle accelerator.

A world first was reached between 3am and 4am in Geneva, when physicists declared the two beams "stable", meaning that the two beams were focused but deliberately not collided.

However, at 6:17am, a corrector magnet tripped in part of the 27km ring of the experiment, according to Tejinder Virdee, a professor of physics at Imperial College London. Corrector magnets work inside the LHC to steer the protons so they remain "on axis" — that is, so they perform the fine focusing needed to fire the beams on target, said Virdee.

"It's a trip, but they can resolve it," Virdee added.

The second glitch that halted the experiment happened at around 8:15am. The LHC has a quench protection system, which dumps the large amounts of energy from the beams to protect the experiment in the event of a quench.

The quench protection system is overly sensitive, Cern director of communications James Gillies said, adding that the whole system had experienced the glitch.

"It was a general perturbation of the system," said Gillies. "The quench protection system is very sensitive." The system was installed after a liquid helium leak derailed the LHC in September 2008.

The glitch was caused by the magnetic coupling between two of the quadrupole magnets tripping in the Super Proton Syncratron (SPS), the last accelerator that the beams go through.

"It was a freak event that dumped the beam," said Gillies. "Once the beam is reinjected we'll switch the SPS off."

Each time the beams stop circulating, they require a full cycle of ramping up. The energy is then ramped down and back up again to the injection energy of 450 giga-electron volts (GeV). At about 10am, beams were being injected into the machine prior to circulation.

The LHC, which is funded by a group of countries including the UK, is a 27km ring deep beneath the French-Swiss border.

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