Cern Large Hadron Collider machine restarts
| By Paul Rincon Science reporter, BBC News |
 The Atlas detector will join the hunt for the Higgs boson particle |
The Large Hadron Collider (LHC) experiment has been restarted after a hiatus of 14 months.
Engineers working on the machine achieved a stable, circulating proton beam just after 2100 GMT on Friday.
The LHC is housed in a 27km-long circular tunnel about 100m beneath the French-Swiss border.
The experiment is designed to smash together beams of protons in a bid to shed light on the nature of the Universe.
The LHC has been shut down for repairs since an accident in September 2008.
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.
"It's great to see beam circulating in the LHC again," said Cern's director-general Rolf Heuer.
Particle physicist Jim Virdee says that scientists are excited that the LHC is coming back online
"We've still got some way to go before physics can begin, but with this milestone we're well on the way."
Engineers sent their first beam all the way round the LHC's 27km circumference after 1930 GMT on Friday.
The beams themselves are made up of "packets" - each about a metre long - containing billions of protons. But they would disperse if left to their own devices.
Electrical forces had to be used to "capture" the protons. This keeps them tightly huddled in packets, for a stable, circulating beam.
There are some 1,200 "superconducting" magnets which form the LHC's main "ring".
These magnets bend proton beams in opposite directions around the main "ring" at close to the speed of light.
At allotted points around the tunnel, the proton beams cross paths, smashing into one another with enormous energy. Large "detector" machines located at the crossing points will scour the wreckage of these collisions for discoveries that should extend our knowledge of physics.
 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 |
Among other things, 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.
Engineers first circulated a beam all the way around the LHC on 10 September 2008.
But just nine days later, an electrical fault in one of the connections between superconducting magnets caused a tonne of liquid helium to leak into the tunnel.
Liquid helium is used to cool the LHC to its operating temperature of 1.9 kelvin (-271C; -456F).
The machine has been shut down ever since the accident, to allow repairs to take place.
Professor Norman McCubbin from the UK's Rutherford Appleton Laboratory in Didcot, added: "I'm sure every particle physicist has been feeling just a little bit impatient as the 're-start' of the LHC has drawn nearer. It's great to see beams circulating again."
The damage caused to the collider meant 53 superconducting magnets had to be replaced and about 200 electrical connections repaired.
Engineers have also been installing a new early warning system which could prevent incidents of the kind which shut down the experiment.
Cern has spent some 40m Swiss Francs (£24m) on repairs to the collider.
No comments:
Post a Comment