Fermilab Today Friday, April 27, 2007

Fermilab Update on Inner Triplets

To strengthen the support structure of the magnets in the "inner triplet," cartridges will be attached to one of the ends of the Q1 magnet and to one of the ends of the Q3 magnet.
The Q1 magnet (blue) with cartridges (red) attached.

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.

Review of proposed magnet repairs
A team of experts from CERN, from CEA-Saclay (a French national laboratory), and from Brookhaven National Laboratory met at CERN on April 24 and 25 to review proposed solutions to the problems that caused the failure of a Fermilab-built "inner triplet" of superconducting magnets during a routine pressure test on March 27. Physicists and engineers from Fermilab and Lawrence Berkeley National Laboratory participated in the review.

Each triplet contains three superconducting magnet assemblies, a cryogenic and power distribution box for the magnets, and associated structures. The triplets will focus particle beams prior to particle collisions in the Large Hadron Collider, now under construction at CERN. The pressure test took place in the accelerator tunnel.

The CERN review team examined the mechanical design of the inner triplet to make sure that there are no further hidden defects and conducted a review of the proposed in-situ repairs.

The reviewers examined the proposed repair method to hold the magnet's cold mass in place inside its cryostat, or outer metal jacket, to keep the magnet from moving when it experiences an asymmetric longitudinal force. During the pressure test, the existing magnet support structure broke in response to such a force.

The solution presented to the review panel will use four long metal cartridges installed parallel to the magnets long axis. The cartridges will be welded to the magnet's cold mass and to a bracket attached to the cryostat. The review panel made detailed recommendations for verifying the cartridges' ability to hold the magnet in place under a wide variety of possible conditions during accelerator operations.

The magnets will remain in the accelerator tunnel during the installation of the cartridges.

The panel also examined a proposed back-up solution in case continuing tests and analyses identify problems with the cartridge method. Further minimal tests and analysis are proceeding in parallel for the back-up plan.

Reviewers examined minor potential problems in the cryogenic and power distribution boxes for the inner triplets and in the structures that connect the elements of the triplet. Solutions to these problems, now under development, were also addressed.

Scientists and engineers from CERN, Fermilab, Lawrence Berkeley National Laboratory and Japan's KEK Laboratory will continue to share the tasks involved in testing, analyzing, installing and testing the triplet repairs. The present plan is to repair one set of triplets in time for the next pressure test in June.

LHC Magnet Update Archive

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