Accelerator Report: Preparing the LHC and its injector complex for the 2024 lead-ion run

In the early morning of 13 September, the LHC reached a significant milestone, surpassing 100 fb^-1 of integrated luminosity delivered to ATLAS and CMS in a single year – a record – and the figure is still rising. Moreover, LHCb’s integrated luminosity target of 8.5 fb^-1 was reached one day later. Of course, this does not mean that we will cease delivering collisions to the LHCb experiment – the LHC team will do its utmost to further increase the size of LHCb’s dataset.

While the LHC continues to provide proton-proton collisions to the experiments, the injector chain is, simultaneously, providing protons to the fixed target experiments. It is also preparing for the lead-ion physics run, not only in the LHC but also in the SPS North Area and the PS East Area.

After a brief test with magnesium ions from April to May this year, Linac3 was converted back to produce lead ions. The original plan was to inject lead ions into the LEIR machine on 5 August. However, due to a problem with the high-voltage power supply in a 14.5 GHz generator that feeds the Linac3 source, this was delayed. Following repairs to the generator, Linac3 restarted on 19 August and, that same day, the first lead ions were available for LEIR.

Because of this two-week delay, the LEIR beam commissioning schedule had to be adjusted. Studies to improve LEIR's performance were cancelled and a fast-tracked plan was introduced to ensure that lead-ion beams were ready in time to be delivered to the SPS.

On 17 September, as planned, the first lead ions were successfully injected and circulating in the SPS. Since the SPS usually operates with a high beam duty cycle and has little flexibility for unscheduled additions, special commissioning blocks for the lead ions were included in the injector schedule for the start of the year.

On 18 and 19 September, from 8 a.m. to 6 p.m., a short ion cycle (14.4 seconds) was added to the SPS supercycle (see image), allowing the SPS team to perform the first part of the lead-ion beam commissioning in the accelerator. For the next steps, a longer ion cycle (57.6 seconds) is required. However, this long cycle would significantly extend the SPS supercycle, reducing the efficiency for both the protons and the ion beam users. To manage this efficiently, six dedicated 10-hour commissioning blocks have been scheduled between 1 and 30 November, during which the long ion cycle will be the sole focus of the SPS supercycle. This will allow the team to set up the final lead-ion beam for the LHC, including the slip-stacking process.

Finally, at least two versions of the lead-ion beams will be prepared in the SPS: one of 57.6 seconds for the LHC, incorporating the slip-stacking process; and another for the users in the SPS North Area, which will involve slow extraction but no slip-stacking and will be 25.2 seconds long.

The four-week physics run for the SPS North Area users is scheduled to start on 4 November, followed by the LHC lead-ion physics run on 6 November, which will last 2.5 weeks. The lead-ion physics programme in the PS East Area is set to start on 11 December.

Due to the fast-tracked commissioning process in LEIR, valuable time was lost for studying and improving machine performance, as well as for addressing issues encountered during the 2023 lead-ion run. However, the LEIR team will use all available time to recover as much as possible of the lost study time between the six dedicated commissioning blocks.