III.13 — CERN LIU project: beam dynamics aspects and solutions

The goal of the LHC Injectors Upgrade (LIU) project was to increase the intensity and brightness in the LHC injectors in order to match the challenging requirements of the High-Luminosity LHC (HL-LHC) project, while ensuring high availability and reliable operation of the injectors complex throughout the whole HL-LHC era. Fulfilling this goal required identifying the main performance limitations across all LHC injectors (Linac2, the Proton Synchrotron Booster (PSB), the Proton Synchrotron (PS), the Super Proton Synchrotron (SPS)) and then implementing a combination of extensive hardware modifications and new beam dynamics solutions in order to overcome them. The beam dynamics solutions were studied, tested and, where possible, implemented operationally already during the LHC Run 2 (2014–2018). The great majority of the LIU hardware modifications were implemented during the 2019–2020 CERN accelerators shutdown. This chapter describes the rationale behind the main baseline choices of the LIU project and the evolution of the various project phases, before concluding on the expected beam parameter reach and actual commissioning. It will solely address the upgrade of the proton injector chain, which better matches the pedagogical scope of this contribution.