Small accidents spell big trouble for supercollider
22 September 2008
GENEVA — Scientists expect startup glitches in the massive, complex machines they use to smash atoms.
But the unique qualities of the world’s largest particle collider mean that the meltdown of a small electrical connection could delay its groundbreaking research until next year, scientists said Sunday.
Because the Large Hadron Collider operates at near absolute zero – colder than outer space – the damaged area must be warmed to a temperature where humans can work. That takes about a month. Then it has to be re-chilled for another month.
As a result, the equipment may not be running again before the planned shutdown of the equipment for the winter to reduce electricity costs. That means Friday’s meltdown could end up putting off high-energy collisions of particles – the machine’s ultimate objective – until 2009.
"Hopefully we’ll come online and go quickly to full energy a few months into 2009 so in the long term, this may not end up being such a large delay in the physics programme," Seth Zenz, a graduate student from the University of California, wrote on the site of the US physicists working at the European Organisation for Nuclear Research, or CERN.
"It’s obviously a short-term disappointment, though, and a lost opportunity," he wrote.
CERN spokesman James Gillies said the repair operation will last until close to the usual winter shutdown time at the end of November. There has been some discussion that the new equipment could operate through the winter, but no decision has been made, he said.
The melting of the wire connecting two magnets Friday would have taken only a couple of days to repair on smaller, room-temperature accelerators that have been in use for decades, Gillies said.
Gillies said particle accelerators using superconducting equipment at Fermilab outside Chicago and at Brookhaven National Laboratory in New York state had similar problems starting up, but have been operating smoothly since then.
"Once they settled in they seem to be pretty stable," Gillies said.
At the 10 September launch of the collider, beams of protons from the nuclei of atoms were fired first at the speed of light in a clockwise direction though a fire-hose-sized tube in the tunnel. Then proton beams were fired in the counter clockwise tube.
Michael Hauschild, a German physicist working at CERN, said that success exceeded expectations.
"If the LHC is running, it’s a fantastic machine," he said. "But it was always clear to all of us, both accelerator physicists and scientists, that problems as present can happen."
Jos Engelen, CERN’s chief scientific officer and deputy director-general, said the startup showed that the LHC can handle complex operations.
"We have encountered a weakness in one particular connection during very final hardware commissioning," Engelen told The Associated Press by e-mail. "It is tough, but it can happen. We will make the repair and resume the very successful operation of the accelerator."
A transformer failed outside the cold zone about 36 hours after the collider’s launch. That was repaired and the machine was ready again a week after it was shut down.
But the goal of the LHC – shattering protons to reveal more about how the tiniest particles were first created – was still weeks away because the equipment has to be gradually brought to the higher energies possible at full power.
"This was the last circuit of the LHC to be tested at high current before operations," Gillies said. "There are an awful lot of these connections between wires in the machine. They all have to be very well done so that they don’t stop superconducting, and what appears to have happened is that this connection stopped being superconducting."
Superconductivity – the ability to conduct electricity without any resistance in some metals at low temperatures – allows for much greater efficiency in operating the electromagnets that guide the proton beams.
Without the superconducting, resistance builds up in the wires, causing them to overheat, he explained.
"That’s what we think happened," Gillies said. "This piece of wire heated up, melted, and that led to a mechanical failure."
Gillies said experts have already gone down into the 27-kilometre circular
tunnel under the Swiss-French border to inspect the damage.
"By Monday I suspect we’ll know more," he said.
Gillies said there is plenty for scientists at CERN to do between now and the startup of experiments, including studying cosmic rays that pass through collider’s massive detectors.
[AP / Expatica]