CERN's LHC Expected to Restart Within Days

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Protons may whizz around the Large Hadron Collider (LHC) as early as this weekend, after a successful operation to fix a short circuit which had delayed its restart, according to Paul Collier, head of beams at CERN.

CERN, Europe’s particle physics laboratory near Geneva, Switzerland, had planned to switch on the souped up collider last week after a two-year shutdown for upgrades (see LHC 2.0: A new view of the Universe). But the lab put its plans on hold after the machine developed a fault.

Teams attributed the glitch to a piece of metal debris in a diode box, part of the safety system of one of the machine’s superconducting magnets. The debris short-circuited the magnet’s power supply.
Engineers’ first attempt to remove the fragment appears to have been successful. On 30 March they sent an electrical discharge through the circuit to burn away the metal causing the fault. “It’s a bit like deliberately blowing a fuse,” says Collier.

Tests carried out today on the circuit suggest the remedy worked. “It passed. The short is gone,” says Collier. Engineers must now re-install monitoring and protection equipment before they can re-power the circuit. “However, it looks good,” he adds. “We hope to be ready to take beam sometime during the weekend.”

If quick methods to remove the piece of metal had failed, the delay could have stretched to months. Removing the fragment manually would have meant warming the magnet to room temperature before cooling it down again to its operating temperature of 1.9 kelvin, just above absolute zero.


The world’s most powerful particle collider is poised to roar once again into action after a two-year hiatus. At the end of March, the Large Hadron Collider (LHC) at CERN, Europe’s particle-physics lab near Geneva, Switzerland, will start smashing particles together at a faster rate and with higher energies than ever before. “We’re standing on the threshold of a completely new view of the Universe,” says Tara Shears, a particle physicist at the University of Liverpool, UK.
The first run began in earnest in November 2009 and ended in February 2013. The LHC collided particles — mainly protons but also heavier particles such as lead ions — at high enough energies to discover the Higgs boson in 2012, which garnered those who predicted the subatomic particle a Nobel prize.

In the next run, set to last three years, energies will rise to an eventual 14 teraelectronvolts (TeV; see ‘Hardware rebooted’). One hope is that higher energies will produce evidence for supersymmetry, an elegant theory that could extend the standard model of particle physics (see ‘Desperately seeking SUSY’).They could also shake out particles of dark matter, the invisible substance that is thought to make up 85% of the matter in the Universe (see ‘Decays decoded’).

More collisions will enable more-precise study of the Higgs’ nature (see ‘The Higgs factory’) and will provide clarity on anomalies hinted at in run 1 (see ‘Known unknowns’).

“In the first run we had a very strong theoretical steer to look for the Higgs boson,” says Shears. “This time we don’t have any signposts that are quite so clear.”

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