The Cryogenic System and Planned Cryogenic Tests For the Future High Luminosity LHC IT Magnet String

The high luminosity upgrade of the Large Hadron Collider will require the replacement of the triplet of final focusing superconducting magnets at interaction points 1 and 5 with a new set of helium II cooled magnets. To validate the technologies and assembly procedures and to investigate the collective effects, a string of magnets representative of the final HL-LHC configuration, will be installed in the SM18 test facility at CERN in 2021. The local cryogenic distribution connected to the string of magnets will also be representative of the final configuration. This paper first describes the cryogenic configuration of the magnet string and the functional cryogenic requirements for the operation and test program. The cryogenic parameters for the different circuits and operation phases are presented. The paper details the cryogenic test program foreseen to investigate the specific challenges of cooling Nb3Sn magnets and their beam screens during high heat load (several hundred watts at 1.9 K), steady state, and transient operation. The paper presents the complete cryogenic system planned for the string, its integration into the SM18 facility, the required adaptation of the SM18 cryogenic infrastructure, and the conceptual design of the main components.