Magnet supports give way at LHC

Ian McKellen has an alibi

A routine test of the almost-complete Large Hadron Collider (LHC) at CERN ended in near disaster last week when the structure supporting the particle accelerator's key magnets failed.

The so-called magnet assembly was made by FermiLab, the US department of energy's particle accelerator lab and chief rival to CERN in the hunt for the very small. Despite this rather obvious conspiracy theorist magnet, the researchers at CERN insist there are "no recriminations".

The structure that failed was holding up the accelerator's "triple magnets". These focus the accelerating proton beams whizzing around the LHC's 27 kilometre tunnel at four points. When they are switched on, they exert a considerable force, and at this point in the test they failed.

Ex-fermilab scientist Peter Limon, now firmly ensconced at CERN, told New Scientist that people were disappointed the supports were not up to the job.

He added that there was still uncertainty as to the extent of the damage to nearby equipment. No information is available yet about whether the failure will mean a delay to the switch on date for the accelerator. ®

CERN and FermiLab have issued a lengthy statement on the situation. Edited for brevity, this is what they had to say:

"On Tuesday, March 27,  a Fermilab-built quadrupole magnet, one of an “inner triplet” of three focusing magnets, failed a high-pressure test at Point 5 in the tunnel of the LHC accelerator at CERN.

The asymmetric force generated by the pressure of the test broke the supports in magnet Q1 that hold the magnet’s cold mass inside the cryostat, which also resulted in damage to the electrical connections.

Computer-aided engineering calculations... show that the support structure in the magnets was inadequate to withstand the associated longitudinal forces. This is an intrinsic design flaw that must be addressed in all triplet magnets assembled at Fermilab.

Review of engineering design documentation reveals that the longitudinal force generated by asymmetric loading was not included in the engineering design or identified as an issue in the four design reviews that were carried out.

The immediate goal is to have a repaired triplet in another sector of the accelerator ready to participate in a pressure test scheduled for June 1."

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