Mechanical analysis of the Nb₃Sn 11 T dipole short models for the High Luminosity Large Hadron Collider

Abstract

For the Large Hadron Collider luminosity upgrade, two of the NbTi 8.3 T main bending dipoles will be replaced by two shorter Nb 3 Sn 11.2 T dipoles to create space for the installation of collimators in the dispersion suppression region. With the aim to verify the design features, several 2 m long 11 T models have been constructed and tested at CERN. During the fabrication and assembly of, so far, seven single and two double aperture short model magnets, several challenges were identified and tackled. These include reproducibility in coil fabrication and assembly procedure, as well as control of mechanical stresses in the conductor and surrounding structure. In order to limit coil over-compression and improve reproducibility, the cable insulation was re-optimized. In addition, a review of the collaring procedure of the 11 T magnet was launched with the goal of reducing the risk of conductor degradation due to excessive stress. In this paper, the main fabrication and assembly steps are described, including the description of the actions taken to resolve the identified weakness.

Advanced examination of Nb3Sn coils and conductors for the LHC luminosity upgrade: a methodology based on computed tomography and materialographic analyses

“…Short 11T magnet models manufactured and tested at CERN started to exhibit quench performance issues circa 2018 [12,13] while performance degradation after a sequence of electromagnetic and warm-up/cooldown cycles was subsequently observed on several 5.3 m-long, twin-aperture 11T dipole magnets. Following a successful short model magnet (known as MQXFS) program [14,15], the first two 7.2 m long quadrupole magnets (known as MQXFB) prototypes manufactured and tested at CERN in 2020 and 2021 (MQXFBP1 & 2), exhibited performance limitation below nominal current [16].…”