The Large Hadron Collider, the world's most powerful particle accelerator, is drawing near to its long-awaited reboot. More than a year after the European collider's initial start-up was quashed by a helium leak caused by a faulty electrical connection, particle beams have been injected into the collider, known as the LHC, and may be guided fully through its rings in the coming hours.

"We're hoping to have beam overnight in the LHC," James Gillies, a spokesperson for CERN, the European particle physics lab that operates the LHC, said Friday. "So, all being well, we will wake up tomorrow morning and there will be circulating beams." By 3:30 P.M. Eastern Standard Time on Friday, a beam had completed a full lap of the tunnel in the clockwise direction, with a counterclockwise beam still to come, according to CERN's Twitter feed.

Proton beams have been run through segments of the collider's 27-kilometer underground circumference near Geneva this fall, but putting the entirety of the collider ring through its paces as is now underway will be a much truer test of the machine's fortitude. In September 2008 it was just nine days after beam circulation that the LHC experienced its crippling breakdown. Since that time the LHC's minders have been dealing with the aftermath of the helium leak, painstakingly repairing, upgrading and recommissioning the machine to get it back in working order and to try to forestall a repeat incident.

If all goes according to plan, the LHC's operators could break new ground with the machine in short order. "One thing we didn't do last year was use the LHC as a particle accelerator," Gillies says. "Last year we injected beams and circulated beams before we had the breakdown, but we didn't accelerate them. So once we've got a beam circulating, we'll start testing the acceleration systems of the LHC."

Although the LHC is designed to accelerate protons to a whopping seven TeV (tera–electron volts), CERN has long said that it plans to work the machine's energy up over time. The initial target for accelerated beams will be 1.2 TeV, which would already surpass the current top dog among particle accelerators, the Tevatron collider at Fermi National Accelerator Laboratory in Batavia, Ill.

Particle collisions, accomplished by steering a clockwise particle beam into a counterclockwise one, are "the other capability that must be demonstrated before we can really say the LHC is up and running," according to Gillies. Whether the first collisions will be conducted with 1.2 TeV beams or with scaled-down energies has not been decided, he says. "Either way, any collisions that we do this year is really calibration work. It's not new physics, if you like," Gillies adds. "The real physics research program doesn't get underway until January."

Among the tantalizing discoveries that could await the LHC are the Higgs boson, which lends mass to other particles, and a possible identification of dark matter, an invisible material thought to pervade the universe that has not been observed directly.

New physics or not, the prospect of simply getting the machine running is cause for excitement at CERN, where many years and billions of dollars have been spent in anticipation of the LHC's arrival. "There's a buzz about the place, I must say," Gillies says. "It's been a long time."