Large Hadron Collider broke down hours after launch

Plans to begin smashing particles at the Large Hadron Collider (LHC) may be delayed after a magnet failure forced engineers to halt work.

The failure, known as a quench, caused around 100 of the LHC's super-cooled magnets to heat up by as much as 100C.

The fire brigade were called out after a tonne of liquid helium leaked into the tunnel at Cern, near Geneva.

The LHC beam will remain turned off over the weekend while engineers investigate the severity of the fault.

A spokesman for Cern told the BBC it was not yet clear how soon progress could resume at the £3.6bn ($6.6bn) particle accelerator.

While the failure was "not good news", he said glitches of this kind were not unexpected during testing.

Scientists have now replaced the faulty transformer and the ring in the 17-mile circular tunnel under the Swiss-French border.

It has also now been cooled back down to near absolute zero on the Kelvin scale (minus 459.67 degrees Fahrenheit) - the most efficient operating temperature.

When the transformer malfunctioned, operating temperatures rose from below 2 Kelvin to 4.5 Kelvin, warmer than the normal operating temperature.

Steve Giddings, physics professor at the University of California, Santa Barbara, said: "This is arguably the largest machine built by humankind, it is incredibly complex, and involved components of varying ages and origins, so I'm not at all surprised to hear of some glitches.

"It's a real challenge requiring incredible talent, brain power and coordination to get it running."

Now the transformer has been replaced and the equipment rechilled, scientists expect to prepare experiments in the coming week.