The world's most powerful particle accelerator returned to operation on Friday following a refrigeration glitch that forced it to stop days after opening.

The European Organisation for Nuclear Research (Cern) said that the problem affecting a cooling system for high-powered magnets designed to steer beams of particles around the Large Hadron Collider's 27-kilometre tunnel had been resolved.

A 30-ton transformer had failed last Thursday, Cern's spokesman, James Gillies, told the AFP news agency.

It took about a week to replace the equipment and to get the accelerator's tunnel back to as low as -271 Celsius, which is colder than deep outer space.

Its purpose is to recreate the conditions one trillionth of a second after the Big Bang more than 13 billion years ago and thus help scientists understand the formation of the universe.

The world's most expensive and complex science experiment took nearly 20 years to complete and cost SFr6 billion ($5.46 billion). Located underground outside the city of Geneva, it spans the border between Switzerland and France.

In compliance with the JTI standards

More: SWI swissinfo.ch certified by the Journalism Trust Initiative