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Accelerator Report: The CERN accelerator complex is awakening from hibernation


Accelerator Report: the CERN accelerator complex is awakening from hibernation
The PS Booster Vistar, clearly showing that the Individual bunch beam (LHCINDIV) is injected (column. Inj.) accelerated (column Acc.) and extracted (column Ej. E10) on all 4 rings to the beam dump. (Image: CERN)

The 2022–2023 year-end technical stop (YETS) is defined as 17 weeks beam-to-beam in the LHC, which is two weeks longer than the standard YETS and was introduced in response to the energy crisis. The last LHC beam of 2022 was dumped in the early morning of Monday, 28 November; 17 weeks later, on Monday, 27 March 2023, we plan to inject the first beam of the year into the LHC.

Although this first beam is a single-bunch beam with reduced intensity, the injector complex needs to be commissioned well in advance. The LINAC4 hardware therefore already began recommissioning on Monday, 13 February, only 11 weeks after the accelerator was stopped. During that time, maintenance was carried out, and a new, more efficient, H- source was installed. In the subsequent beam commissioning period that started on 20 February, the beam was brought through LINAC4, all the necessary parameters were adjusted and the performance of the new source was tested using the higher intensity beam. After the first accelerating structure, the radio-frequency quadrupole (RFQ), the beam current usually measures 25 mA. With the new source, the experts managed to bring this up to 35 mA, an increase of 40% with a similar transmission efficiency. For the 2023 physics run, 25 mA will remain the default current, but further studies to push the performance of LINAC4 and the PS Booster are planned for later this year.

On Friday, 3 March, following two weeks of hardware commissioning, the beam was injected into the PS Booster at 10.15 a.m. In just over an hour, the beam had been captured, accelerated, synchronised, and extracted to the beam dump. This is the point where the tedious work of adjusting the machine starts, after which the various operational beams will be set up and fine-tuned. The first beam will have to be ready for when the PS completes its two-week hardware commissioning period on Friday, 10 March. The PS will then have one week to prepare the first beam for the beam commissioning of the SPS, which today is about halfway through its three-week hardware commissioning period. It will then be the turn of the SPS to prepare the single-bunch LHC beam to be delivered to the LHC on Monday, 27 March, to awaken the LHC from its hibernation.

Throughout the accelerator complex, various beam types will then be re-adjusted to be delivered for physics, starting with the PS East Area around Easter and followed by the other fixed-target facilities in the subsequent weeks. The first collisions in the LHC are expected around 22 April, heralding the start of a relatively short but intense physics run that is scheduled to end on 30 October.