Accelerator Report: LHC performance stays on track and is cruising towards the target

Over the past two weeks, despite many LHC fills ending due to the machine's protection systems rather than by the LHC Engineer in Charge (LHC-EiC), the LHC has still performed very well, with an overall availability of around 75% and beams in collision for nearly 60% of the time. Thanks to this, the integrated luminosity passed the 90 fb⁻¹ mark on 28 September, nearing the forecast curve. As I write, the integrated luminosity is 92 fb⁻¹, only 2 fb⁻¹ short of the forecast 94 fb⁻¹, with five more days still available before the start of the third machine development (MD) block, which will last four days. After that block, just 24 days remain in the 2025 proton run. Reaching the target of 120 fb⁻¹ is therefore feasible, though it will remain a challenge. Fortunately, the issues with the non-conforming RF finger module and the collimator affected by a vacuum leak are not limiting operational performance.

The injector chain is gearing up to deliver the necessary beams for the LHC lead-ion physics run, scheduled to begin on 15 November. The full chain for lead ions involves Linac3, LEIR, the PS and the SPS. Beyond the LHC, lead-ion beams are also used in the PS East Area and the SPS North Area.

The Linac3 source, which produced oxygen and neon ions in July, has now been converted to produce lead ions, and beams were successfully delivered to LEIR for the start of its commissioning on 15 September. Commissioning in LEIR, which is carried out only on working days, progressed smoothly, allowing lead ions to reach the PS a week ahead of the scheduled date of 6 October. The SPS is next in line, expecting its first lead-ion beams on 13 November, which will be used to commission two separate ion cycles: one for fixed-target physics in the SPS North Area and one for the LHC.

Beam commissioning in the PS can proceed fully in parallel with proton delivery to users. In the SPS, however, only part of the commissioning can run in parallel. Most requires dedicated time slots without proton delivery to the North Area. For this purpose, three dedicated 10-hour sessions are planned, on 15 and 29 October and 5 November. Lead ions are then scheduled to be sent to the LHC on 8 November, one week before the start of physics.

Meanwhile, the delivery of protons for fixed-target physics across the injector complex is running at full pace, with excellent availability from all machines, although a fraction lower than in 2024.

The PS Booster (PSB) has so far accelerated 1.6 × 10²⁰ protons, of which 9.97 × 10¹⁹ (62%) have been delivered to ISOLDE. So far, 30% of PSB protons have gone on to the PS, where the n_TOF facility is the largest user, having received 2.62 × 10¹⁹ protons, or 56% of all PS protons.

With ten weeks still to go until the end of the 2025 physics run, the total number of protons delivered will continue to rise, while the distribution between the different users is expected to remain similar. As for beam availability, the hope is not only to maintain the current levels but to improve them slightly, aiming to at least match last year's excellent figures.