Published online 9 February 2009 | Nature | doi:10.1038/news.2009.90
Updated online: 9 February 2009

News

LHC faces further delay

Collisions won't come before November.

No collisions before November.CERN

Those waiting for the world's most powerful particle accelerator to start work will have to wait a little longer. An official announcement expected within days is likely to say that the Large Hadron Collider (LHC) will not begin providing data until November — more than a year after its planned start date.

The LHC was seriously damaged during power tests in September last year (see 'Eight-month delay for LHC'). In October, CERN, the LHC's host laboratory near Geneva, Switzerland, estimated that the machine would be ready for a restart by the summer, but it now seems unlikely that protons will be collided before November. The delay is due to additional safety protocols and complex repair schedules, according to Steve Myers, CERN's director for accelerators and technology. "The initial schedule was rather optimistic," he says, adding that he firmly believes that the November date for collisions will be achievable.

To appease impatient high-energy physicists, the laboratory will probably run the machine (albeit at reduced powers) for a ten-month stretch from November until the autumn of 2010. The cost of electricity alone, which is more expensive during the winter, would be an additional €8 million ($10.5 million).

False start

When it does eventually run, the LHC will use superconducting magnets to collide protons together at close to the speed of light — creating a shower of heavy particles for physicists to study.

In the accident in September, a weld between two sections of the superconducting wire failed. In the minutes after the accident, several tonnes of liquid helium used to cool the magnets vaporized, creating a pressure build-up that wrenched magnets from their concrete stands. In total 53 superconducting magnets must be removed so they can be cleaned, repaired or replaced.

Further diagnostic work has since found two more bad welds in magnets in other sectors. Myers says that CERN is investigating how the bad welds escaped being detected in quality-control testing by both the manufacturer and the lab.

To fix the welds, the other sectors of the machine must be warmed up, and that means that liquid helium must either be shunted around the ring or put into storage. This "playing musical chairs with helium", says Myers, will slow the progress of the repairs.

New safety regulations also state that workers can no longer power any sector of the machine if others are in the tunnel because a major helium leak, such as the one in September, could cause an oxygen shortage.

Lost time

The delays are having repercussions for the thousands of physicists working on the detectors designed to monitor the collisions. Graduate students in particular, who are depending on LHC data for their PhD theses, are finding it difficult, according to Pauline Gagnon, an experimental physicist with ATLAS, one of the two largest detectors. Perhaps a dozen have left the ATLAS project, she estimates, but the vast majority of physicists are understanding. "We have no choice, we cannot run the risk of another incident," she says. "You don't want to screw up twice."

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Rachel Yohay, a graduate student at the University of Virginia in Charlottesville who is working on the Compact Muon Solenoid, the LHC's other large detector, says that the mood is "largely conciliatory". Even with the delay, she says, there's still plenty of work that can be done. The detector's team will use the extra time to install more subsystems and further debug the equipment using data from high-energy cosmic rays.

Under CERN's compromise plan, the LHC will accelerate its protons to just 5 teraelectronvolts, well below its designed 7 teraelectronvolts. At that reduced power, "the chances of finding something will be limited", Gagnon says. But, she adds, it is still possible that the LHC will see some new physics: "We could be lucky for a change." 

Updated:

CERN has announced that the LHC will begin collisions in late October and will run through the winter period with only a brief break at Christmas. More "here":http://www.symmetrymagazine.org/breaking/2009/02/09/cern-management-confirms-new-lhc-restart-schedule/.

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