As you may have read in a previous Bulletin article, the SPS has a new beam dump, located at Point 5 of the accelerator. This new device, which is nine metres long and shielded with steel, concrete and marble, was built as part of the LHC Injectors Upgrade (LIU) project, in preparation for the High-Luminosity LHC (HL-LHC). “It was commissioned in April 2021, during the post-LS2 restart of the SPS. Everything went as planned,” says the engineer in charge of the project, Antonio Perillo Marcone of the SY-STI-TCD section. “Thanks to the beam dump’s new instruments – in particular, the new beam instrumentation monitoring system, which records the profile of the beam when it enters the dump – we can track the absorption of the particles in real time. In addition, new probes allow us to monitor the temperature inside the dump.” As well as allowing real-time tracking, these new tools transmit data that is valuable for refining the digital models used to develop beam dumps in general, which are of increasing importance for CERN’s future projects.
But before smashing into the beam dump, the particles circulating in the SPS must be deflected from their path by kicker magnets. “Six of these magnets have been installed in Long Straight Section 5 of the SPS, which leads to the beam dump. Five of them were already part of the SPS and a sixth has been added in preparation for the increased beam intensity of the future HL-LHC and the new configuration of the SPS beam dump system,” says Étienne Carlier, project leader of the SPS beam dumping system upgrade project.
Unfortunately, while being commissioned in the accelerator, the new magnet revealed some unexpected limitations: “During tests in situ, the magnet was unable to withstand voltages above 35 kV, i.e. its maximum nominal operating voltage. This surprised us, because these same tests had been carried out up to 38 kV without any problems during the validation phase carried out on the surface, before installation,” explains Étienne Carlier. By opening up and inspecting the spare magnet, which is identical in every respect, the experts were able to put their finger on the problem: “Small ceramic supports, called spacers, were found to be preventing the magnets from withstanding higher voltages,” continues Étienne Carlier. We therefore replaced these parts in the spare magnet, which we then installed in the SPS to replace the defective magnet during the year-end technical stop (YETS).”
The spare magnet, which has been functioning at its nominal voltage since the restart with beam, was reconditioned in the machine during the technical stop, to ensure that it could handle voltages of up to 38 kV. It is currently being conditioned with beam as, being completely new, it releases a lot of particles – a normal process known as “outgassing”. This phenomenon degrades the quality of the vacuum locally, although it does not impede the performance of the SPS.