The wheel-shaped piece of equipment, with a diameter of about 30 feet, was lowered down a 330-foot shaft and fitted with other equipment known as detectors in an underground room the size of a cathedral.
"It's exciting but at the same time there is a feeling of relief," said Robert Aymar, director-general of the European Organization for Nuclear Research, as he watched.
The startup date for the Large Hadron Collider, eagerly awaited by scientists planning to use it for studying the makeup of matter and the universe, has not been set. Aymar said the $2 billion project, under construction since 2003, appeared to be on target for completion by this summer.
"For such a huge, complex enterprise, difficulties are there," Aymar, a French scientist, told The Associated Press in an interview at CERN, as the organization is known from its French acronym.
The wheel installed Friday contains a cluster of tightly packed detector chambers made up mostly of either copper or aluminum. Their function is to trace the particles that come off protons when they collide at the speed of light.
"When the wheels were shipped from where they were assembled at CERN, I had butterflies in my stomach," Frank Taylor, a senior research scientist at the Massachusetts Institute of Technology. "In fact, I mentioned to somebody it was valium in the morning and, if successful, champagne in the afternoon. Now I've just gone to coffee."
He said hard work remains for his team, which must connect the rest of the detector to the wheel that was assembled from precision parts made in several countries.
