Linac4 design report

Linear accelerator 4 (Linac4) is designed to accelerate negative hydrogen ions for injection into the Proton Synchrotron Booster (PSB). It will become the source of proton beams for the Large Hadron Collider (LHC) after the long shutdown in 2019–2020. Linac4 will accelerate H– ions, consisting of a hydrogen atom with an additional electron, to 160 MeV energy and then inject them into the PSB, which is part of the LHC injection chain. The new accelerator comprises an ion source and four types of accelerating structures. The particles are accelerated first to 3 MeV energy by a Radio-Frequency Quadrupole (RFQ), then to 50 MeV by three Drift Tube Linacs (DTL) tanks, then to 100 MeV by seven Cell-Coupled Drift Tube Linac (CCDTL) modules, and finally to 160 MeV by twelve Pi-Mode Structures (PIMS). A chopper line placed between the RFQ and the first DTL tank modulates the linac beam at the PSB injection frequency. Linac4 includes transfer and measurement lines up to the PSB injection, where the ions are stripped of their two electrons to leave only protons. Linac4 is 76 metres long and located 12 metres below ground. The first low-energy beams were produced in 2013 and after the commissioning of all accelerating structures the milestone energy of 160 MeV was reached in 2016. Linac4 will be connected to the PSB during the long shutdown of 2019–20, after which it will replace the 50 MeV Linac2 as source of protons for the LHC. The Linac4 is a key element in the project to increase the luminosity of the LHC during the next decade.