CERN researchers restarted the Large Hadron Collider (LHC) on Friday afternoon, sending a beam of protons around the 27-kilometer (18-mile) underground, circular tunnel housing the machine for the first time since September 2008.

Back then, a bad electrical connection cut short the $10 billion (6.7 billion euro) machine's debut, exposing shortcomings in its design and construction.

Over the past year, engineers at CERN's laboratory, located on near Geneva on the border between Switzerland and France, have been repairing about 200 electrical connections and 53 superconducting magnets. They've also installed an early warning system which should help prevent incidents of the type which shut down the experiment.

The purpose of the experiment is to replicate conditions at the time of the "big bang," in other words, the beginning of the universe. Physicists hope to prove the existence of the Higgs boson, also known as "the God particle." It's this particle which supposedly gives matter in the universe its mass.

To create such conditions, the LHC has to generate collisions between protons travelling at 99.9 percent of the speed of light. In its first few months of operation, the machine will collide protons at energies of 3.5 trillion electron volts (TeV), but it was designed to run at energies of seven TeV.

Baguette-eating bird causes short circuit

Attempts to restart the collider suffered an initial setback this month, when a bird picking at a piece of baguette caused a short circuit at one of the points where the electricity supply from the grid enters the collider from above ground.

"The problem related to the high voltage supply," CERN spokeswoman Christine Sutton said at the time. "We get mains voltage from the grid, and there was an interruption in the power supply, just like you might have a power cut at home. The person who went to investigate discovered bread and a bird eating the bread."

The system was restored several hours later, but the "baguette incident" again showed just how susceptible the massive machine, which took 20 years to build, is to interruptions.

Accordingly, researchers at CERN decided to keep the fanfare about the re-launch of the LHC to a minimum.

dc/afp/ap

Editor: Sean Sinico