Thirteen months after a testing failure revealed serious design flaws in nine sets of "inner triplet" magnets for the Large Hadron Collider, engineers switched on the first of the repaired sets, ran it for an hour and subjected it to a highly stressful test that, in the words of Fermilab's Jim Kerby, "releases a lot of energy, so if something is going to shake loose or be a problem, this is one event that could cause it to happen."
The magnets performed just fine, to the great relief of about 50 scientists, engineers and technicians who worked on the repairs and countless others who made substantial contributions. Kerby reported the results Friday in an email, and Fermilab Director Pier Oddone described them Tuesday in a column entitled "Triplet Crown:"
A crown is what the folks who have worked over the last year to get the LHC triplets ready for operations at the Large Hadron Collider deserve... This is the first time that a triplet has worked at specifications (equivalent energy of 7 TeV) as a system of three magnets with all its power and cryogenics interconnections in place. We have come a long way from where we were a year ago.
"It's a combination of relief and a thrill," Kerby told me in a phone interview from CERN, the European particle physics laboratory on the Swiss-French border where the LHC is scheduled to turn on this summer. "There's been an awful lot of hard work by an awful lot of people to get this far, and it's a thrill to see it come together, finally."
There are eight sets of inner triplet magnets in the LHC (the ninth is a spare.) Their job is to focus the particle beams into the four areas where particles will collide.
Within each set, two of the magnets, called Q1 and Q3, were designed at Japan's KEK laboratory and built by industry. The third, Q2, was designed and built at Fermilab. Fermilab also assembled all the magnets into cryostats and shipped them to CERN.
In March 2007, researchers subjected one of the inner triplets to some of the most extreme conditions they can expect to face during normal operations. Superconducting magnets like these have to stay very cold in order to conduct electricity without any resistance. If even a small part of the magnet "goes normal"--loses its superconductivity, and begins to resist the flow of current--this releases a lot of energy in a very small space, which can damage or even destroy the magnet. These events are known as quenches, and while they might seem a bit scary, they do occur from time to time during the running of a collider. In response, heaters fire up and and heat up the whole magnet, dissipating the energy over the magnet's entire volume so it does no harm.
After the first set of inner triplets failed the quench test, investigators quickly found the problem: Certain support structures for the magnets were not designed to withstand the longitudinal forces they experienced during testing. These supports have been repaired, along with other equipment damaged by the test failure.
On Thursday night, Kerby and his team ran a normal operating current through a set of inner triplet magnets for the first time. "It went to nominal operating current and came back down without a problem, which is good," he said. "This is what we want."
They powered the triplets up again and fired the quench protection heaters. "This is a big jolt," Kerby said. Again, the magnets passed.
Finally--by now it was Friday, Geneva time--the crew powered up the magnets again and ran them for an hour.
Kerby, who is a mechanical engineer, has been involved in the design of the magnets from the beginning. He became the Fermilab project leader in in 1998 and is now the US LHC accelerator project leader.
Although the original test failure was not exactly pleasant, he says, it was far better than the alternative--discovering the problem after the collider is already in operation.
"The best thing you can do is tackle the problem head-on. If there's a goof, you fix it,'' he said.
Kerby said it was especially gratifying to see the way people from so many places--including Fermilab, KEK, CERN, the US Department of Energy and Brookhaven and Lawrence Berkeley national laboratories--stepped forward to help find a solution.
"That part is just spectacular," he said. "You call on the expertise of various people--not just the design people or the people to fix it, but the procurement people, who in our case happen to be at Fermilab. I probably got only a small fraction of their time, but for that fraction they knew exactly what they needed to do, and really pulled it off." And that, he said, is just one of many examples.
Of the eight inner triplets in the LHC, he said, all but one have been successfully pressure tested. Four are chilled nearly down to operating temperature, and another is on its way.
As for the powering-up tests, he said, "One down, seven to go."
