Accelerator Report: The accelerator complex is gradually waking up from the winter shutdown

The 2026 Chamonix Workshop took place last week and brought together the accelerator and experimental communities to review the recent operational performance of the accelerator complex and discuss challenges ahead. The programme included a look back at the 2025 operation as well as an overview of this year's final stretch of Run 3 and of the post-LS3 (Long Shutdown 3) operation. With LS3 approaching, discussions centred on the upcoming HL-LHC upgrades, as well as consolidation activities in the North Area and ISOLDE, and on the construction of the HiECN3 facility. The workshop concluded with an outlook on CERN's longer-term future, including progress on the Future Circular Collider (FCC) project and the implications of the European Strategy for Particle Physics.

As for the current status of the accelerator complex, the transition into the 2026 run - the last year of Run 3 - is particularly rapid. Responsibility was transferred from the year-end technical stop (YETS) coordination team to the Operations Group (BE-OP) to perform the Departmental Safety Officer (DSO) tests, followed by equipment and control checks, machine checkout and, finally, beam commissioning.

The commissioning of Linac4 and the PS Booster (PSB) has progressed smoothly and according to plan. Owing to the very short YETS, little or no work was carried out on the equipment, which allowed the reuse of the 2025 machine settings. This approach proved successful and is a strong indication of the maturity and stability of the systems.

Thanks to the extensive preparation by the equipment groups and an efficient hardware commissioning phase, the PS hardware commissioning was completed in only four days. As a consequence, the PS received its first beam on 24 January, three days ahead of schedule. Most of the PS beams were recommissioned rapidly, allowing the first beam to be delivered to the first physics users of 2026: n_TOF on 2 February and the East Area on 4 February.

The H^- beam has returned to ELENA on schedule, marking another important milestone in the restart of the low-energy antiproton programme. In the Antiproton Decelerator (AD), the DSO tests in the target area and the ring have just been completed. The first proton beam on the AD target is planned for 13 February, with the start of physics scheduled for 27 February.

In the SPS, DSO tests are under way to validate the machine and its safety systems, while the hardware tests across the accelerator are nearing completion. Provided that these final tests conclude as planned, the start of beam commissioning is expected for 13 February.

Meanwhile, on the LHC side, DSO tests were successfully carried out on 6 February, marking the shift of responsibility from the YETS coordination team to the operators for the last machine of the complex. Over the coming two weeks, more than 1600 superconducting circuits will be progressively tested up to their nominal currents, corresponding to operation at 6.8 TeV.

Once this extensive powering campaign is completed, only the machine checkout phase will remain between the end of the YETS and the arrival of beam. During machine checkout, all accelerator systems are tested together to verify the overall readiness of the technical infrastructure, before beam injection and circulation can begin (planned for 21 March).

With the injector chain performing strongly and the LHC restart advancing according to plan, the accelerator complex is steadily waking up from the YETS and moving towards the start of the 2026 physics programme. The coming weeks will be decisive as commissioning activities continue across the complex.