London, October 18 : Details of last month's accident at the Large Hadron Collider (LHC), the world's premier particle accelerator, have confirmed that the machine will not restart before late May or early June 2009.
The LHC is the world's largest and highest energy particle accelerator complex, intended to collide opposing beams of protons with very high kinetic energy. The machine circulated its first particle beams on 10 September 2008, but a few days later had to suspend operations due to equipment failure.
Officials at CERN, Europe's particle-physics laboratory near Geneva, Switzerland, have said that the time till June 2009 is needed to overhaul a sector of the 27-kilometre-long machine, after an electrical failure on 19 September caused some 6 tonnes of ultra-cold liquid helium to leak into its tunnel.
The accident report said that during the September 19 test, a weld in a superconducting wire connecting two magnets heated above its operating temperature.
That in effect turned the wire into a resistor - causing a massive 8.7 kiloamps of power to arc through the liquid helium and puncture into the surrounding vacuum vessel.
The amount of helium released was larger than the valves were designed to handle.
In just milliseconds, the arc managed to vaporize a "significant fraction" of the nearly metre-long connection between the two magnets, according to Jim Strait, an accelerator physicist at the Fermi National Accelerator Laboratory in Batavia, Illinois, who has been consulting on the accident investigation.
The liquid helium flowed through the hole and into an insulating region of vacuum, which was meant to work as a thermos to keep the magnets cool.
Relief valves designed to allow the helium to escape were overwhelmed and, within seconds, the pressure in the machine became powerful enough to wrench magnets off their concrete supports.
According to a report in Nature News, a preliminary report issued on 16 October said that as many as 29 of the nearly 10,000 magnets used to guide the accelerator's proton beam will need to be replaced.
Further magnets may need to be removed and inspected, and modifications must also be made to prevent future accidents.
"It's a serious incident," said James Gillies, a spokesman for the laboratory.
Still, CERN is confident it has the resources to make the repairs.
No more than 24 dipole magnets and 5 quadrupole magnets were damaged; CERN has 30 dipole magnets - each weighing 35 tonnes - in reserve, as well as sufficient quadrupoles, according to Gillies.
Replacement magnets are already being tested in a facility above the buried accelerator tunnel.
Nevertheless, Gillies said that the damage will take all of CERN's winter shutdown period to repair.