The Large Hadron Collider will come back online in late summer 2009 at the earliest, and not in June as previously expected.
The LHC was shut down in September, nine days after it was first fully powered up, following a helium leak caused by an electrical fault. The world's most powerful particle accelerator is designed to smash beams of protons into each other, test fundamental physics theories, and help understand the nature of matter.
How the Large Hadron Collider works
The machine is located at the European Center for Nuclear Research (CERN), where it straddles the Swiss-French border.
CERN director Robert Aymar said in October that the LHC would come back online at the beginning of April 2009, following CERN's annual maintenance period. Earlier this month, that date was revised to June 2009.
However, the plan now is to restart the experiment in late summer next year, CERN's head of communications, James Gillies, told ZDNet UK on Friday.
The accelerator operations group at CERN came up with two possible plans to restart the LHC, details of which are included in a CERN presentation. According to the document, written by Jorg Weninger, a member of the operations group, "Plan A" called for a restart of the experiment in late summer 2009, with the beam energy and intensity limited to minimize the risk of another accident. "Plan B" delayed switching on the beam until there had been a complete upgrade to the pressure-relief system, which would mean the LHC would be restarted in 2010 at the earliest.
Gillies confirmed Plan A rather than Plan B will now be implemented. "The priority is to get collision data from the experiment," said Gillies. "The LHC will run next year."
The liquid helium leak in September caused damage to the LHC, mainly as a result of the helium expanding as it warmed. Under Plan B, CERN would have installed pressure-release valves on each of the super-conducting magnets' cryostats. To do that, it would have had to warm the whole 17 miles of the LHC ring.
Each of the eight sectors of the LHC are independently cooled, Gillies said, and at the moment three of the sectors are warm. The plan is to modify these sectors, which will include fitting pressure-release valves to the cryostats on the dipole magnets, to try to prevent damage in the event of another accident. The remaining five sectors will be kept cool, and they will have pressure-release valves fitted as and when other repairs or modifications are needed.
The beam energy of the LHC is designed to eventually be 7 tera electron-volts (TeV), said Gillies, who added that CERN was hoping the experiment would run at approximately 5 TeV next year.
"The five undamaged sections can run at 5 TeV, and the rest of the machine can run at 4 TeV." said Gillies. "The highest we're hoping to run next year will be lower than 7 TeV."
Tom Espiner of ZDNet UK reported from London.