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Progress made in Large Hadron Collider repair

Final replacement magnet has been lowered into the particle accelerator's tunnel. LHC is set to go back online in September--a year after an accident shut it down.

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 on Thursday the completion of the LHC's above-ground repair work. 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 17-mile 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.

This photo from last year shows two of the most severely broken interconnects, which were between the magnets in LHC sectors three and four. CERN

The LHC went offline in September 2008--just days after the LHC was turned on for the first time.

The problem started when a faulty electrical connection between two of its magnets caused a malfunction in the cooling system that keeps the machine below -271 degrees C. That malfunction subsequently led to a liquid helium leak, resulting in a need for widespread repairs. By CERN's latest reckoning, the system will be turned on again in late September of this year.

"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.

Images: Where particles, physics theories collide
Click image for a 2008 gallery on the LHC. Maximilien Brice for CERN

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.

David Meyer of ZDNet UK reported from London.