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Accelerator Report: Already a fifth of the way there


The whole CERN accelerator complex and its associated experimental facilities have been fully operational for some time now, so the time is ripe to review the first part of this year’s run and look forward to what is still to come.

At the LHC, first collisions with just a few bunches occurred on 6 April. Meaningful physics data taking can only begin when collisions take place with at least 1200 bunches per beam, and this milestone was reached on 14 April. It means that, out of the 147 days allocated to proton-proton collisions this year, 32 have already been completed, representing just over 20% of the 2024 proton run.

During these initial 32 days, the LHC machine was available 67.2% of the time with stable beams in collision 45.2% of the time. The goal is to achieve a stable beam time ratio of at least 50%. Such figures are quite normal in the early stages of an annual run, a period during which various teething problems and challenges are identified and addressed, as discussed in my last report.

Luminosity production is also progressing according to schedule, as can be seen in the graph below. So far, the integrated luminosity collected has reached 17.5 fb-1, which is nearly 20% of the 2024 target of 90 fb-1. To reach this target, we need an average of about 0.8 fb-1 per day. Recently we have seen a record production of 1.23 fb-1 in just 24 hours, which demonstrates the LHC’s impressive potential to meet and possibly even exceed our target.

The predicted and achieved luminosity curves for ATLAS and CMS. The blue areas indicate the machine development (MD) periods, the red area the Van de Meer run, and the green one the technical stop. (Image: CERN)

Today, the LHC is performing the Van de Meer run, a crucial process used to calibrate the luminosity measurements in the four main LHC experiments (ALICE, ATLAS, CMS, LHCb).

This follows the first block of machine development (MD) sessions that took place on 13-15 May, during which experts conducted various tests and studies, including further investigation into the collimator hierarchy breaking that occurred in April.

On 18 May, the LHC will resume its primary task of producing luminosity. This production period will continue until the second MD block that is scheduled to start on 5 June and will be followed by a 5-day technical stop to carry out essential preventive and corrective maintenance before the summer holiday season. During the summer, the LHC will continue its luminosity production.

An overview of the beam availability of the different injectors and experimental facilities. The availability of each machine takes into account the non-availability of the upstream machines. (Image: CERN)

Not only is the LHC performing well, but the injector complex is also achieving a high level of beam availability for its experimental users. Physics in the injector complex kicked off on 22 March in the PS East Area. With the run scheduled to end on 2 December, the East Area has already completed over 20% of its 2024 run. Meanwhile the antimatter factory, which was the last facility in the injector complex to start beam operation, began delivering antiprotons to its experiments on 22 April, so just over 10% of its scheduled physics time for 2024 has now elapsed.

Linac4, the first link in the proton injector chain, has posted an average availability of 97.3% since its start after Long Shutdown 2 (LS2). It has posted availability of 95.7% so far in 2024, about 1.6% less than usual. This can mainly be attributed to a series of faults that led to the replacement of a klystron in March.

The injectors will continue their routine beam delivery to the experimental facilities until 12 June, when they too will interrupt beam production for a 4-day technical stop. Afterwards, it will be business as usual once more and the experiments can look forward to good beam delivery over the summer.

As we continue through the year, the achievements so far set a promising pace for the remaining months.