Just as the end of a run gives us the chance to look back and reflect on our achievements, the start of a new year is the perfect opportunity to focus on the plans and challenges ahead. The maintenance activities scheduled for the 2024-2025 year-end technical stop (YETS) are in full swing and, so far, no unexpected issues or showstoppers that could delay the restart of the accelerator complex have arisen.
Every year, the accelerator complex is restarted through a carefully planned process that combines sequential and parallel workflows. This approach optimises the time available for YETS maintenance activities, while maximising physics time during the operational run. The goal for the recommissioning is to deliver all beams on schedule, with the quality and performance required by the experiments.
For the LHC, maintenance activities are scheduled to conclude on 13 March, when responsibility for the LHC will transfer from the Technical Coordination group in the Engineering department (EN-ACE) to the Operations group in the Beams department (BE-OP). The first crucial milestone in preparing the LHC for operation will be the personnel access and safety system tests, conducted by the Beams Departmental Safety Officer (DSO tests). These tests will enable us to verify and validate the functioning of the safety system, which is designed to ensure that no one can be inside the LHC when it is operational and that the machine cannot be started if personnel are present in the tunnel.
Following the validation of these safety systems, the LHC's hardware will be powered up and thoroughly tested over a 2.5-week period. This process will culminate in a three-day machine check-out, scheduled to begin on 2 April. During this period, the LHC will be operated as if beams were circulating, but without the actual beam, a bit like an orchestra's dress rehearsal, where all the instruments play together even if they are not yet perfectly tuned. Once the "orchestra" has been fine-tuned, the LHC will be ready to receive its "musical score", the proton beam, and begin its symphony of accelerating and colliding beams.
Before the full physics programme begins, a six-week period of beam recommissioning and intensity ramp-up will take place, bringing us to 1200 bunches per beam, a number that is considered meaningful for physics, on 19 May.
Proton collisions will be paused in the last week of June for a technical stop, followed by a special physics run in early July. For the first time ever, the LHC will inject, accelerate and collide oxygen ions. After a four-day set-up period, four days of oxygen-oxygen collisions will provide data for physics.
Once the oxygen run is complete, a two-day calibration run (Van der Meer scans) will mark the return of proton physics, paving the way for a productive summer and early autumn of data collection.
The proton run is scheduled to end on 3 November and the lead-ion run to start on 15 November, for a period of 21 days, followed by two days of machine development (MD). At 6.00 a.m. on 8 December, the final beams of 2025 will be dumped, marking the end of operations and the start of the next YETS.
Of course, for the LHC to be ready to start the recommissioning with beam on 5 April, the injector chain must be recommissioned well in advance. In fact, the Linac4 source is scheduled to start up next week, on 29 January, in order to deliver beam to Linac4 on 19 February. A week later, on 27 February, the Linac4 beam will be injected into the PS Booster. Shortly after, on 5 March, the PS Booster will transfer its beam to the PS for the latter's beam recommissioning. The SPS will receive the beam on 14 March and then prepare the LHC beam in time for delivery to the LHC before 5 April.
Meanwhile, each machine in the injector chain will also prepare beams for the fixed-target experiment facilities. These include ISOLDE, the PS East Area, n_TOF and the SPS North Area. Beams will also be prepared for the Antiproton Decelerator (AD) target, which is crucial for producing the antiprotons needed by the AD and ELENA decelerators. The ELENA machine is then expected to deliver low-energy antiprotons for physics to its experiments on 28 May. The AWAKE and HiRadMat beams will also be prepared for first delivery on 21 April and 5 May, respectively.
As for ion operations, Linac3 and LEIR will start up early in April 2025, so as to be ready to deliver oxygen-ion beams to the PS on 26 June. The PS will transfer these beams to the SPS by 10 June in preparation for the four-day oxygen physics run in the LHC and the nine-day oxygen physics run in the SPS North Area, starting on 9 July.
After the conclusion of the oxygen run, the injector chain will be converted to deliver lead ions. These will be supplied to the LHC, the SPS North Area and the PS East Area, before the injectors also shut down at 6.00 a.m. on 8 December.
But before looking ahead to the end of the run, let's focus on what promises to be an exciting and successful year and, of course, stay tuned for more news on the recommissioning of our accelerator complex…
