The failure of a single electrical connection in the Large Hadron Collider caused the equipment to shut down just nine days after the machine's launch with great fanfare Sept. 10.
CERN scientists had already determined that one connection out of 10,000 was badly soldered, causing electrical resistance that led to the fault, but it has taken until now for the supercooled equipment to warm up enough so that experts could examine it and decide what needed to be fixed.
It had already been decided that it was impossible to get the machine up and running again before the annual maintenance time starts in November to save expenses when electricity costs are high.
It takes a month to warm the collider gradually to room temperature from its operating temperature at near absolute zero, colder than outer space. Once the repairs are made, it will take another month to recool it.
The collider uses superconductivity - the ability of some metals to conduct electricity without any resistance in the extreme cold
- to operate the electromagnets, which guide the beams of protons until the particles collide with each other.
The shattering of the protons in the collisions helps scientists to understand better how they are made and how they make up everything and everyone in the universe.
The failure was caused by an electrical arc that punctured an enclosure holding the liquid helium used to keep the collider cold, said a CERN statement. Some six tons of helium leaked out as a result, three times as much as originally thought.
The remaining 114 tons of liquid helium in the collider was unaffected by the leak, said Gillies.
He said CERN has enough spares to make any needed replacements of the equipment, but that the repairs will take the whole winter.
"We'll be pretty busy," Gillies said.
He said the costs of the repairs had yet to be determined, but that CERN would be able to cover them out of its budget and that it wouldn't have go to the 20 European member countries to ask for more funds.
The examination also found that the fault sent a "soot-like dust" into the firehose size pipes through which the beams of protons are guided at nearly the speed of light.