Preparing the LHC and its injector for the lead ion experiment in 2024

In the early hours of September 13, the LHC reached a major milestone, delivering more than 100 fb-1 of light to ATLAS and CMS over the course of a year, a record that continues to climb, and the next day LHCb reached its light output goal of 8.5 fb-1.

Of course, this does not mean that we will stop providing collisions to the LHCb experiment: the LHC team will continue to do everything in its power to further increase the size of LHCb’s dataset.

While the LHC continues to provide proton-proton collisions for experiments, the Injector Chain is simultaneously supplying protons to fixed target experiments, and lead ion physics experiments are being prepared not only at the LHC but also in the SPS North Area and the SPS East Area.

After a brief test run with magnesium ions in April and May of this year, Linac3 was reconfigured to produce lead ions again, with the original plan being to inject lead ions into the LEIR instrument on August 5.

However, this was delayed due to problems with the high-voltage power supply of the 14.5 GHz generator that powers the Linac3 source. After the generator was repaired, Linac3 was restarted on 19 August, the same day the first lead ions were available at LEIR.

This two-week delay required an adjustment to the LEIR beam commissioning schedule: studies to improve LEIR performance were halted and a rapid plan was put in place to have the lead ion beam ready in time to reach the SPS.

The first lead ions were injected and cycled into the SPS as planned on September 17. Because the SPS typically operates at a high beam duty cycle and has little flexibility for unscheduled additions, the injection schedule at the beginning of the year included a special commissioning block of lead ions.

A short ion cycle (14.4 seconds) was added to the SPS supercycle from 8am to 6pm on September 18th and 19th (see image above), allowing the SPS team to perform the first part of a commissioning of the lead ion beam inside the accelerator. The next step requires a longer ion cycle (57.6 seconds); however, this longer cycle would significantly extend the SPS supercycle, reducing the efficiency for both proton and ion beam users.

To manage this efficiently, six dedicated 10-hour commissioning blocks are scheduled between 1st and 30th November, during which the SPS supercycle will focus exclusively on the long ion cycle, allowing 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 beam will be prepared at the SPS: one 57.6-second long beam incorporating the slip-stacking process for the LHC, and one 25.2-second long with slow extraction but no slip-stacking for users in the northern area of ​​the SPS.

The four-week physics experiment for SPS Northern Area users is scheduled to begin on November 4, followed by two and a half weeks of LHC lead-ion physics experiments on November 6. The PS Eastern Area lead-ion physics program is scheduled to begin on December 11.

The expedited commissioning process for the LEIR has meant valuable time has been lost to study and improve the machine’s performance, as well as to address any issues that arise during lead-ion operation in 2023. However, the LEIR team will use all available time to recover as much of the lost research time as possible across the six dedicated commissioning blocks.