The faulty transformer has been replaced and the ring in the 17-mile circular tunnel under the Swiss-French border has been cooled back down to near zero on the Kelvin scale - minus 459.67 degrees Fahrenheit - the most efficient operating temperature, said a statement by CERN, as the organization is known.
When the transformer malfunctioned, operating temperatures rose from below 2 Kelvin to 4.5 Kelvin - extraordinarily cold by most standards, but warmer than the normal operating temperature. CERN had not reported any problems with the project since its launch Sept. 10, but issued its statement shortly after The Associated Press called asking about rumors of troubles.
Physicists said it wasn't surprising problems would occur in getting a huge and immensely complicated collection of equipment like the Large Hadron Collider up and running smoothly.
"This is arguably the largest machine built by humankind, is incredibly complex, and involves components of varying ages and origins, so I'm not at all surprised to hear of some glitches," Steve Giddings, physics professor at University of California, Santa Barbara. "It's a real challenge requiring incredible talent, brain power and coordination to get it running."
Judith Jackson, spokesman for the Fermi National Accelerator Laboratory in Batavia, Ill., echoed that view.
"We know how complex and extraordinary it is to start up one of these machines. No one's built one of these before and in the process of starting it up there will inevitably be glitches," she said.
Fermilab is home to the Tevatron, an accelerator that collides protons and antiprotons in a 4-mile-long underground ring to allow physicists to study subatomic particles. Jackson said transformer malfunctions can be common and aren't dangerous.
"These things happen," she said. "It's a little setback and it sounds like they've dealt with it and are moving forward." The Large Hadron Collider is designed to collide protons in the beams so that they shatter and reveal more about the makeup of matter and the universe.
After it was started up Sept. 10, scientists circled a beam of protons in a clockwise direction at the speed of light. They shut that down, then turned on a counterclockwise beam.
"Several hundred orbits" were made, CERN's statement said.
On the evening of Sept. 11, scientists had succeeded in controlling the counterclockwise beam with equipment that keeps the protons in the tightly bunched stream that will be needed for collisions, but then the transformer failed and the system was shut down, the statement said.
The clockwise beam was not on at the time. Now that the transformer has been replaced and the equipment rechilled, scientists expect to try soon to tighten the clockwise beam and prepare experiments in coming weeks, the statement said.
Before the problem occurred, scientists had said it would probably be several weeks before the first significant collisions were attempted.
Associated Press writer Carley Petesch in New York contributed to this report.