GENEVA — A 30-ton transformer that cools the world’s largest particle collider malfunctioned, forcing physicists to stop using the atom smasher just a day after launching it to great fanfare, the European Organization for Nuclear Research said yesterday.

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 absolute zero — or 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 September 10, but issued its statement shortly after the Associated Press called asking about rumors of troubles.

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 September 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 September 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.