LHC report: switch was flipped, and beams were dumped

LHC dipole magnets in the tunnel
CERN’s Large Hadron Collider
(Image: CERN)

On Monday, 28 November at 6 o’clock in the morning, the LHC Engineer in Charge flipped the switch and the last proton beams of 2022 made a final turn around the LHC before being discarded into the dedicated beam dumps. This marked the end of the first of four years of Run 3 and the start of the year-end technical stop (YETS), a mere 21 weeks after the very first collision at 6.8 TeV per beam.

2022 was, without a doubt, a commissioning year: our teams encountered problems related to Long Shutdown 2 (LS2) updates, as well as beam intensity limitations due to heat load, in particular in sector 7-8. Thankfully, these issues were effectively addressed, and alternative beam schemes were tested and used to overcome the limitations.

All in all, the machine and beam performance exceeded initial expectations. The integrated luminosity prediction for 2022 was 25 fb-1, based on a beam availability factor of 30%, which matches average values for commissioning years. In fact, the beam availability factor for a major part of the physics run was closer to 50%, despite two extended stops in May and August-September and the longer YETS, which was brought forward by two weeks due to the worldwide energy crisis. Along with the good beam performance, this availability resulted in the delivery of 40 fb-1 for both ATLAS and CMS. However, the four-week lead run, which was scheduled at the end of the year, was cancelled in favour of proton physics.

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The LHC would not have achieved this impressive number of collisions without the considerable flexibility and good performance of the injector complex, which concluded its second year of Run 3 (already!) on 28 November 2022. The injectors are reaping the benefits of the LHC Injector Upgrade undertaken during LS2, and the intensity ramp-up towards HL-LHC beam parameters has made commendable progress over the past few months – the PS and its Booster have actually reached these parameters already in 2022.

Besides feeding protons to the LHC, the injectors have once again served the rich and varied fixed-target physics programmes of ISOLDE, the East Area, the n_TOF facility, the Antiproton factory, AWAKE, HiRadMat and the North Area. As an example, the SPS provided a record 2.3×1019 protons to the North Area while improving the quality of the beam spill, as requested by the users.

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Left: The integrated number of protons sent to the North Area in the years 2017-2022. Right: The weekly number of protons sent to the North Area, with a record during summer 2022. (Courtesy of K. Li)

Although the lead ion run was cancelled at the LHC, lead ions were successfully fed to the North Area for a two-week physics run, down from four weeks. In addition, the commissioning of the slip-stacked LHC ion beam in the SPS was completed, and LHC experiments did register some lead-lead collisions as part of a two-day lead ion test run in November, during which slip-stacked bunches were injected.

Today, instead of particles, technicians and engineers are whizzing around the tunnels to ensure that the accelerator complex is properly maintained, and to prepare it for 2023 – another year of hopefully efficient operation and promising data taking.

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