- Fermilab 'Dumbfounded' by Fiasco That Broke Magnet
GENEVA, April 4, 2007 -- In what is being described as a "pratfall on the world stage," the quadrupole magnet that Fermilab built for the Large Hadron Collider (LHC) particle accelerator failed high-pressure testing dramatically last week, resulting in a loud "bang" and a cloud of dust in the LHC tunnel. It was the first time that the three magnets and their cryogenic and electrical connections were tested together.
The 43-ft-long quadrupole magnet, one of an "inner triplet" of three focusing magnets, was built by Fermilab (Fermi National Accelerator Laboratory) of Batavia, Ill., as part of the LHC, which will be the world's largest particle accelerator when operational and contains about 9300 magnets. Scientists will use the LHC to recreate the conditions just after the Big Bang created the universe by colliding two beams of protons traveling in opposite directions at close to the speed of light.
Fermilab designed and built nine of the magnet assemblies for CERN and conducted four engineering reviews between 1998 and 2002. The supercooled magnets focus the particle beams prior to collision at each of four interaction points around the accelerator. They focus the beam down to the smallest possible size at the collision points, maximizing the chances of two protons smashing head-on into each other.
Q1 quadrupole magnet – CERN and Fermilab are working to identify repairs to the structures that hold the cold mass (blue) in place within the cryostat (orange) in each magnet of the triplet on either side of the LHC's four interaction points. The Q1 magnet of each triplet is the magnet closest to the interaction point (IP). (Images: Fermilab)
In a statement posted yesterday on its Web site, Fermilab said the "asymmetric force generated by the pressure of the test" broke the supports in magnet Q1 that hold its cold mass inside the cryostat, damaging the electrical connections. The magnet's supports are made of a glass cloth-epoxy laminate. After the failure, Fermilab and CERN calculations found the support structure's design was inadequate to withstand the longitudinal forces generated, which were the same as those expected during the LHC's normal operations.
Cross-section drawing of an inner-triplet quadrupole magnet at one of the support points.
"Last Tuesday we took a pratfall on the world stage," said Fermilab Director Pier Oddone in a message posted yesterday on the lab's Web site. "What the analysis shows so far is that something extraordinarily simple was missed in the design. We do many very complex engineering projects successfully that require sophisticated engineering skills and advanced computing tools. We test the complex features we design thoroughly. In this case we are dumbfounded that we missed some very simple balance of forces.
"Not only was it missed in the engineering design but also in the four engineering reviews carried out between 1998 and 2002 before launching the construction of the magnets. Furthermore, even though every magnet was thoroughly tested individually, they were never tested with the exact configuration that they would have when installed at CERN -- thus missing the opportunity to discover the problem sooner," he said.
Longitudinal force during a pressure test broke the G-11 support structure (green) securing the cold mass (blue) inside the magnet cryostat (not shown).
Fermilab said the status of the cold mass in the Q1 magnet was still being determined, as is the status of the other two magnets in the triplet and the distribution feed box designed to provide supercooling fluids and electrical power to the magnets. The lab said it hopes the repairs won't affect the LHC startup, which is scheduled for later this year. CERN said it hasn't yet determined if the startup will be delayed.
"We have given the top priority in our laboratory to helping CERN fix the problem; we will do everything that is necessary to minimize the impact to the LHC schedule. We also appreciate the offers of assistance that we have received from our partner laboratories KEK, BNL, LBNL and ANL," Oddone said.
"Beyond the immediate fix we must reflect on how we got into this mess," he said, adding that Fermilab will initiate an external review of events from the beginning of the design.
CERN is managing the redesign and repair effort and has scheduled a review for April 24-25 to approve the selected method. Fermilab said the immediate goal is to have a repaired triplet in another section of the accelerator ready to be used in a pressure test scheduled for June 1.
The LHC, being built by the European Organization for Nuclear Research (CERN), is located inside a circular underground tunnel 17 miles in circumference approximately 300 feet beneath the earth on the border of Switzerland and France.
For more information, visit: www.fnal.gov or http://public.web.cern.ch
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