Workers prepare to lower a magnet into the Large Hadron Collider's tunnel.
The restart of the world's biggest particle-smasher is being postponed until late September at the earliest, to allow for the installation of a safety system that would have reduced the amount of damage done during last year's electrical breakdown.
In today's announcement of the additional delay, Europe's CERN physics research center said the Large Hadron Collider should produce its first proton collisions in late October and its first science results next year.
The LHC, housed in a 17-mile-wide ring of underground tunnels on the French-Swiss border, is designed to produce the most powerful subatomic smashups ever engineered by scientists (although cosmic rays in space are thought to reach higher energies).
The $10 billion international effort is expected to shed new light on a whole range of cosmic questions: What is dark matter made of? Why do some particles have mass while others don't? What was the universe like just after the big bang? Does space have extra dimensions we haven't yet detected? Scientists say the machine might even create ultramicroscopic black holes - which they insist would blip back out of existence without harming anything.
There may be no danger of a black-hole blow-up, but a more down-to-earth problem forced a shutdown of the collider shortly after its widely publicized startup last September: A bad electrical splice in the collider ring caused a sudden loss of helium coolant, resulting in major damage to some of the ring's magnets.
CERN, which is making an estimated $29 million worth of repairs during the months of downtime, had hoped that the magnet ring would be cooled down enough to restart the proton beams in early July. But today's announcement said engineers will need some extra time to install a more sensitive system to monitor the electrical resistance in the splices, as well as new pressure-relief valves and other safety measures.
To make up for the lost time, CERN will add extra weeks to the collider's work schedule after the restart. CERN customarily shuts down collider operations for several months during the winter, but toward the end of this year, there'll be only a "short technical stop" for the Christmas season. Except for that short break, the LHC will run straight through to the autumn of 2010, CERN said.
"The schedule we have now is without a doubt the best for the LHC and for the physicists waiting for data," CERN Director General Rolf Heuer said in today's status report. "It is cautious, ensuring that all the necessary work is done on the LHC before we start up, yet it allows physics research to begin this year."
For a refresher on the scientific mysteries, the engineering wonders and the cultural controversies surrounding the LHC, check out our special report on "the Big Bang Machine."