Page last updated at 16:14 GMT, Tuesday, 17 November 2009

LHC nears restart after repairs

Compact Muon Solenoid (Cern)
The Compact Muon Solenoid is one of two multi-purpose detectors at the LHC

The Large Hadron Collider (LHC) could restart as early as this weekend after more than a year of repairs.

But officials have avoided giving an exact date for sending beams of protons around the 27km (17 mile) circular tunnel which houses the collider.

The LHC was first switched on in 2008, but had to be shut down when a faulty electrical connection caused one tonne of helium to leak into the tunnel.

The vast machine is located 100m below the French-Swiss border.

Operated by the European Organization for Nuclear Research (Cern), the LHC will recreate the conditions just after the Big Bang.

Two beams of protons will be fired around the tunnel. These beams will travel in opposite directions around the main "ring" at close to the speed of light.

At allotted points around the tunnel, the proton beams will cross paths, smashing into one another with enormous energy.

Scientists hope to see new particles in the debris of these collisions, revealing fundamental new insights into the nature of the cosmos.

But the first beams to circulate around the collider will be injected at a low energy of about 450 billion electron volts.

For the restart, engineers are determined to take things one step at a time, and officials are not setting hard and fast deadlines.

Once the collider is circulating two beams in opposite directions, engineers will attempt low-intensity collisions.

This will provide scientists with data they can use for calibration purposes.

After this, the beams' energy will be increased so that the first high-energy collisions can take place.

These will mark the real beginning of the LHC's research programme.

Atlas (Cern/C. Marcelloni)
The giant Atlas detector will search for hints of the elusive Higgs boson particle



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