Assembly process and quality control of the magnet cryostats for the HL-LHC project at CERN

Abstract As part of the High Luminosity Large Hadron Collider Upgrade (HL-LHC) at CERN, new focusing quadrupoles, separation and recombination dipoles, and corrector magnets will be installed on either side of the ATLAS and CMS experiments. Specific cryostat designs were developed to allow for the operation of these magnets at 1.9 K. A base design concept is progressed into 19 cryostat types to comply with requirements that depend on tunnel integration, cryogenics, instrumentation, and cold mass dimensions. The assembly process for the cryostats is split into two main phases: Phase 1 involves inserting the cold mass and thermal shield assembly into the vacuum vessel, while in Phase 2 a so-called service module is added to provide specific features and interfaces for installation in the LHC tunnel. In 2022, the production of the first cryostat began following the completion of the design, the procurement of components, the definition of the assembly process, and the availability of a magnet cold mass. This paper presents an overview of the assembly process and the quality controls utilised to ensure consistent, high-quality execution during the assembly of each cryostat. It examines several aspects, such as the specialised tooling utilised during the assembly, how strict leak testing requirements are met, as well as detailing some of the issues encountered and lessons learned.