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Description
The High-Luminosity LHC (HL-LHC) project aims at upgrading the existing LHC machine to increase its integrated luminosity by a factor of ten. A key aspect of this upgrade are the inner triplet (or low-β) quadrupole magnets, the MQXF, which utilize Nb3Sn superconducting magnet technology and reach a conductor peak field of 11.3 T. The MQXFB version, manufactured at CERN, is characterized by a magnetic length of 7.2 m, making it the longest Nb3Sn accelerator magnet ever realized. A total of ten MQXFB series magnets are needed for HL-LHC (eight to be installed and two spares). These magnets rely on a system of water pressurized bladders and keys to pre-tension the aluminium shrinking cylinder at room temperature and to apply pre-stress to the coil-pack. The coil pre-load increases after cool-down to 1.9 K thanks to the larger thermal contraction of the aluminium shrinking cylinder with respect to the rest of the magnet components. Since this structural design is used for first time in an accelerator magnet, the accumulated experience of assembling 80% of the magnets provides valuable insights for the potential application of Nb3Sn technology in future colliders. This paper analyses the main measurables for the mechanical assembly of the MQXFB series magnets and assesses the reproducibility of the production. The main lessons learned during the fabrications process are also described.
