The final replacement magnet for the Large Hadron Collider has been lowered into the giant particle accelerator's tunnel.
The European Organization for Nuclear Research (Cern) announced the completion of the LHC's above-ground repair work on Thursday. Work is still going on below ground to connect the 53 reinstalled magnets, which are used in the scientific project to guide particles around a 27km tunnel under the Alps. The LHC fires two high-speed particles streams around the tunnel in opposite directions, smashing them together at certain points in order to learn more about scientific mysteries such as the nature of matter.
The LHC went offline in September 2008, when a faulty electrical connection between two of its magnets caused a malfunction in the cooling system that keeps the machine below -271°C. That malfunction subsequently led to a helium leak. By Cern's latest reckoning, the system will be turned on again in late September 2009.
"This is an important milestone in the repair process," Steve Myers, Cern's director for accelerators and technology, said in a statement. "It gets us close to where we were before the incident, and allows us to concentrate our efforts on installing the systems that will ensure a similar incident won't happen again."
The magnet that was lowered underground on Thursday was a quadrupole: one of the magnets that focuses the particle stream, rather than one of the dipole magnets that keep the stream on course.
Of the 53 magnets that were affected by the malfunction, 16 were refurbished and put back into the tunnel, while 37 were replaced by spares. The replaced magnets will themselves be refurbished to provide spares for the future.
Apart from the repair itself, the LHC is also gaining systems to monitor its functioning, in order to avoid a repeat of the September incident. Extra pressure valves are also being installed to make any helium releases less disastrous to the project. The incident occurred only days after the LHC was turned on for the first time.