LHC Run 3: the final countdown

18 February 2022
LHC run 3 starts

The successful restart of Linac4 on 9 February marked the start of the final countdown to LHC Run 3. Inaugurated in May 2017 after two decades of design and construction, Linac4 was connected to the next link in the accelerator chain, the Proton Synchrotron Booster (PSB), in 2019 at the beginning of Long Shutdown 2 and operated for physics last year. The 86 m-long accelerator now replaces the long-serving Linac2 as the source of all proton beams for CERN experiments.

On 14 February, Hions accelerated to 160 MeV in Linac4 were sent to the PSB, with beam commissioning and physics to start in ISOLDE on 7 and 28 March. Beams will be sent to the PS on 28 February, to serve, after set-up, experiments in the East Area, the Antiproton Decelerator and n_TOF. The SPS will be commissioned with beam during the week beginning 7 March, after which beams will be supplied to the AWAKE facility and to the North Area experiments, where physics operations are due to begin on 25 April.

Meanwhile, preparations for some of the protons’ final destination, the LHC, are under way. Powering tests and magnet training in the last of the LHC’s eight sectors are scheduled to start in the week of 28 February and to last for four weeks, after which the TI12 and TI18 transfer tunnels and the LHC experiments will be closed and machine checkout will begin. LHC beam commissioning with 450 GeV protons is scheduled to start on 11 April, with collisions at 450 GeV per beam expected around 10 May. Stable beams with collisions at 6.8 TeV per beam and nominal bunch population are scheduled for 15 June. An intensity ramp-up will follow, producing collisions with 1200 bunches per beam in the week beginning 18 July on the way to over double this number of bunches. High-energy proton-proton operations will continue for 3–4 months, before the start of a month-long run with heavy ions on 14 November. All dates are subject to change as the teams grapple with LHC operations at higher luminosities and energies than those during Run 2, following significant upgrade and consolidation work completed during LS2.

Among the highlights of Run 3 are the first runs of the neutrino experiments FASERν and SND@LHC

Among the highlights of Run 3 are the first runs of the neutrino experiments FASERν and SND@LHC, as well as the greater integrated luminosities and physics capabilities resulting from upgrades of the four main LHC experiments. A special request was made by LHCb for a SMOG2 proton-helium run in 2023 to measure the antiproton production rate and thus improve understanding of the cosmic antiproton excess reported by AMS-02. Ion runs with oxygen, including proton-oxygen and oxygen-oxygen, will commence in 2023 or 2024. The former is also long-awaited by the cosmic-ray community, to help improve models of high-energy air showers, while high-energy oxygen-oxygen collisions allow studies of the emergence of collective effects in small systems. High β* runs to maximise the interaction rate will be available for the forward experiments TOTEM and LHCf in late 2022 and early 2023.

On 28 January, CERN announced a change to the LHC schedule to allow necessary work for the High-Luminosity LHC (HL-LHC) both in the machine and in the ATLAS and CMS experiments. The new schedule foresees Long Shutdown 3 to start in 2026, one year later than in the previous schedule, and to last for three instead of 2.5 years. “Although the HL-LHC upgrade is not yet completed, a gradual intensity increase from 1.2 × 1011 to 1.8 × 1011 protons per bunch is foreseen for 2023,” says Rende Steerenberg, head of the operations group. “This promises exciting times and a huge amount of data for the experiments.”

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