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news release:
Fermilab Update on Inner Triplet
Magnets at LHC
Geneva, Switzerland, 20 April 2007:
On Tuesday, March 27, structural supports to a
Fermilab-built quadrupole
magnet, one of an “inner triplet” of three focusing magnets, failed a
high-pressure test in the tunnel of the
LHC accelerator under
construction at
CERN.
The force generated in the pressure test broke the supports in magnet Q1 that
hold the magnet’s cold mass in place inside the cryostat, the magnet’s outer
metal jacket. The support structure broke because it was not designed to
withstand the amount of longitudinal force applied during the pressure test.
Redesign and repair
Since March, teams at CERN and
Fermilab have worked closely together to identify the cause of the failure and
to identify any other potential problems with U.S.-furnished components. The
teams have identified several potential solutions.
The teams have also identified
damage caused by the same pressure test to the cryogenic and power distribution
box, or DFBX, the structure that feeds power and cryogenic fluids to the inner
triplet magnets. Minor repairs will be needed to the DFBXs, which were supplied
by Lawrence Berkeley National Laboratory. LBNL scientists and engineers have
joined the CERN-Fermilab team carrying out the design and implementation of
these repairs.
A review to be conducted at CERN on
April 24 and 25 will examine the selected repair methods to ensure that they
will fix the problems. The reviewers will also look at the inner triplet system
as a whole, as a second check against any unrecognized problems. Scientists and
engineers from Fermilab and LBNL will participate in the review.
All of the repair solutions now
under consideration for the magnet supports and the DFBX can be carried out
without removing the equipment from the LHC tunnel, except for those components
that failed the pressure test..
Solving the LHC magnet problem is
Fermilab’s first priority. The laboratory has pledged to provide whatever
engineering and technical support CERN requests. Lawrence Berkeley National
Laboratory, Brookhaven National Laboratory and KEK Laboratory in Japan have also
offered their help if it is needed.
What must be repaired?
The magnet repair will require
supplementing the original support structure with one strong enough to hold the
magnets in place when they experience longitudinal forces. The new support
structure must also be designed so as to minimize the heat transmitted to the
magnets, so that they can maintain their superconducting state at a temperature
near absolute zero. Additional reinforcement must also be added to two locations
within the piping inside the quadrupole, and to the DFBX.
The three superconducting quadrupole
magnets and the DFBX that failed the pressure test at Point 5 will be removed to
a surface building where they will be inspected and tested. The magnet known to
be damaged, Q1, will be repaired. If necessary, the other two magnets in the
triplet, Q2 and Q3, will also be repaired. They will be replaced in the tunnel
by spare magnets.
Modifications must be made to all
nine of the Q1 and Q3 magnets (two at each interaction region and plus one spare
of each) and to all eight DFBXs. These modifications will be made without
removing the components from the tunnel. The need to modify the third magnet of
each triplet, Q2, is still being studied.
Fermilab and CERN will continue to
provide updates on the LHC triplets as more information becomes available.
FAQ's
Did
magnets explode during the pressure test?
No. Nothing exploded. The longitudinal force applied during the test caused a
quadrupole magnet to move, stretching the pipe connecting it to the adjoining
magnet. The pipe ruptured, making a loud noise and releasing helium gas.
Was
anyone hurt?
No. Safety precautions were followed and no one was injured.
Did
a mistake in mathematics cause the magnet failure?
No. In an engineering oversight, Fermilab magnet designers failed to take into
account the strength of longitudinal forces on the magnet in designing the
magnet’s support structure.
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