The final weeks of Run 3 for the LHC have been among the busiest of its entire operational period. With physics production successfully completed on 14 June, the machine entered a two-week programme dedicated to studies with high-intensity beams, followed by a quench campaign. These activities were scheduled after the completion of the physics programme to avoid any risk to data taking for the experiments.

The primary objective of the high-intensity test was to operate the LHC as close as possible to the beam conditions planned for the High-Luminosity LHC (HiLumi LHC), within, of course, the limitations of the present machine; it was the last opportunity to identify possible weaknesses that could still be addressed.

The test was completed successfully, with a large amount of data collected. Using a variety of beam patterns, the machine systems were probed over a broad range of beam spectra and reached beam intensities and equipment heating representative of the future HiLumi LHC operation.

Overall, the results were encouraging, with a few limitations identified. Vacuum activity was observed in the large vacuum chambers located near Point 2 (ALICE experiment) and in the collimators used to intercept heavy-ion collision debris. These observations will require further analysis and may lead to targeted modifications during Long Shutdown 3 (LS3).

Beyond validating machine performance, the campaign also provided a unique opportunity to perform a wide range of dedicated studies aimed at improving the future HiLumi LHC operation. These included measurements of beam-induced heat loads on the cryogenic system due to electron-cloud effects, investigations of beam stability limits, studies of beam–beam and attempts to reduce the power required from the radiofrequency system, all done at high bunch intensity. The optimisation of beam-loss monitoring to minimise the impact of injection losses for the future HiLumi LHC baseline beam was also performed.

Following the high-intensity programme, the LHC entered a dedicated quench campaign. A quench occurs when a superconducting magnet locally loses its superconducting state. All main dipole and quadrupole magnets are equipped with a cold bypass diode that can take over the current if the magnet quenches. One objective of the campaign was to assess some of these magnets, which are equipped with diodes with a possible manufacturing non-conformity, identified for replacement during LS3. Replacing them is time-consuming and carries its own operational risks. By deliberately quenching the magnets in question before the shutdown, it is possible to pinpoint which of the diodes have the non-conformity, keeping to a minimum the number of diodes that will require repair in LS3.

The campaign also focused on several dipole magnets that had previously exhibited quench signatures similar to those observed in magnets that later degraded during operation. Performing controlled quenches on these magnets helps reduce the risk of future degradation.

Finally, the programme included powering all 600-A corrector magnets installed in the inner triplet assemblies, located on both sides of the experiments’ interaction points. These magnets are exposed to particularly high radiation levels from collision debris, and the tests aimed to better determine the effect of prolonged radiation on the operational limits of these magnets.

Around 80% of the planned tests were completed, providing a wealth of data to be analysed in detail. Besides helping to reduce interventions during the already busy LS3, these results will improve the understanding of the long-term behaviour of superconducting magnet insulation under challenging radiation conditions.

With the completion of these two demanding campaigns, the LHC has now entered LS3 (the Operations team has handed over the key of the LHC to the Accelerator Coordination and Engineering team). The data collected over the past weeks will help ensure that the upgraded machine can fully exploit its unprecedented performance potential.

However, Run 3 isn’t over for everyone just yet… the injectors are continuing their final phase of operation until the end of August. To find out all about these final weeks of Run 3, don’t miss the upcoming Accelerator Reports.

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To make sure you don’t miss anything happening during Long Shutdown 3 (LS3), follow the progress of the work on this new page dedicated to LS3.