"Big Bang" collider to restart with less energy

The giant particle collider built to probe the origins of the universe will restart in November at a lower energy level following its shutdown days after its inauguration last year, CERN said on Thursday.

The announcement by the European Organization for Nuclear Research represented the latest in a series of delays to restart the Large Hadron Collider -- the biggest and most complex machine ever made. CERN had previously set an autumn date.

A technician walks under the core magnet of the CMS (Compact Muon Solenoid) experiment at the European Organization for Nuclear Research CERN (Centre Europeen de Recherche Nucleaire) in the French village of Cessy, near Geneva March 22, 2007. REUTERS/Denis Balibouse

The more than 10 billion Swiss franc ($9.4 billion) machine over-heated and needed to be switched off just nine days after its inauguration in September 2008. Its experiments are meant to reproduce conditions just after the "Big Bang" that scientists believe created the universe.

In a statement, CERN said it planned to restart the Large Hadron Collider with 3.5 Tera-electron volts (TeV) per beam -- less energy than on its initial go -- "because it allows the LHC operators to gain experience of running the machine safely while opening up a new discovery region for the experiments."

It will continue at the lower energy "until a significant data sample has been collected and the operations team has gained experience in running the machine," CERN said. "Thereafter, with the benefit of that experience, the energy will be taken toward 5 TeV per beam."

CERN Director General Rolf Heuer sought to reassure the public and the backers of the machine, whose 27-km (17-mile) collider tunnel lies underground just outside Geneva, that all will run smoothly when it starts up again.

"The LHC is a much better understood machine than it was a year ago," he said. "We can look forward with confidence and excitement to a good run through the winter and into next year."

The experiments would take place at just above absolute zero to recreate the conditions believed to have been present at the beginning of the universe 13.7 billion years ago.

(Reporting by Laura MacInnis; Editing by Charles Dick)