By Paul Rincon
Science reporter, BBC News
The LHC's tunnel runs for 27km under the Franco-Swiss border
Researchers working on the Large Hadron Collider (LHC) say they are delighted with the progress made since the machine restarted on Friday.
One official said the collider had done more in a few hours than it did in five days of operations last year.
The LHC is being used to smash together beams of protons in a bid to shed light on the nature of the Universe.
Housed in a 27km-long circular tunnel under the Franco-Swiss border, it is the world's largest machine.
During the experiment, scientists will search for signs of the Higgs boson, a sub-atomic particle that is crucial to our current understanding of physics. Although it is predicted to exist, scientists have never found it.
The machine was heavily damaged when an electrical fault caused a tonne of liquid helium to leak into the tunnel just nine days after it was first launched in September last year.
During 14 months of repairs dozens of giant superconducting magnets that accelerate particles at the speed of light had to be replaced.
Operated by the European Organization for Nuclear Research (Cern), the LHC will create similar conditions to those which were present moments after the Big Bang.
"We are further advanced now than where we were after five days of experiment last year," said Cern's director of accelerators Steve Myers.
He added that the extra year had allowed researchers to upgrade instrumentation and computer software.
"It's all been pretty positive so far," said James Gillies, director of communications for Cern. "Now, [the team] is knuckling down to the hard work."
He added: "We're not expecting any major milestones to be reached over the next few days."
Operations team members spent Saturday injecting protons into the LHC's 27km-long "ring", attempting to improve the lifetime of the beams.
1 - 14 quadrupole magnets replaced
2 - 39 dipole magnets replaced
3 - More than 200 electrical connections repaired
4 - Over 4km of beam pipe cleaned
5 - New restraining system installed for some magnets
6 - Hundreds of new helium ports being installed around machine
7 - Thousands of detectors added to early warning system
"Right now we've got a beam lifetime of half an hour, which is pretty good for where we are. But ultimately, we want to keep a beam in the machine for 10-12 hours. There's a lot of detailed, nitty-gritty work in order to get there," said Dr Gillies.
Engineers had discussed the possibility of attempting to increase the collider's energy to a record-breaking level of 1.2 trillion electron volts this weekend.
Only the Tevatron particle accelerator in Chicago, US, has so far approached this energy, operating at just under one trillion electron volts.
However, this plan now looks unlikely. Instead, engineers will probably concentrate on preparing the machine for its first low-energy collisions, scheduled to happen in the next 10-15 days.
Progress on restarting the machine went more quickly than expected on Friday. It was not anticipated that engineers would try to circulate a proton beam until 0600 on Saturday at the earliest.
Two stable proton beams had already been circulated in opposite directions around the machine by midnight (GMT) on Friday.
Engineers first circulated a beam all the way around the LHC on 10 September 2008.