HL-LHC Alignment Requirements and Associated Solutions

To increase by more than 10 times the luminosity reach w.r.t the first 10 years of the LHC lifetime, the HL-LHC project will replace nearly 1.2 km of the accelerator during the Long Shutdown 3 scheduled in 2024 [1][2][3]. This paper presents the HL-LHC alignment and internal metrology requirements of all the new components to be installed, from the magnet components to the beam instrumentation and vacuum devices. As for the LHC, a combination of Hydrostatic Levelling Sensors (HLS) and Wire Positioning Sensors (WPS) is proposed for the alignment of the main components, but on a longer distance (210 m instead of 50 m), generating technical challenges for the installation of the stretched wire and for the maintenance of the alignment systems. Innovative measurements methods and instrumentation are under study to perform the position monitoring inside a cryostat of cold masses and crab cavities, in a cold (2K) and radioactive (1 MGy/year) environment, as well as to carry remote measurements in the tunnel of the intermediary components. The proposed solutions concerning the determination of the position and the re-adjustment of the components are detailed in this paper.