The reconfiguration of the cryogenic system, which is essential to provide the additional cryogenic capacity needed to run the LHC with bunch trains (only individual bunches are being injected into the LHC at first), was successfully completed on 7 May. This was promptly followed by a two-day scrubbing run, which was sufficient to achieve the vacuum conditions necessary for the injection of trains of bunches spaced by 25 ns.
Following the scrubbing, the focus shifted to the intensity ramp-up. Some final commissioning and machine optimisation steps also continued, with the aim of reaching 1200 bunches per beam by 19 May.
At 1:20 a.m. on 19 May, the LHC engineer-in-charge started the injection process with the aim of colliding around 1200 bunches for the first time in 2025. After a final round of checks in the injector chain, the SPS delivered bunch trains comprising 4 batches of 36 bunches each. The injection into the LHC was completed at 2:12 a.m., and acceleration of the beam to 6.8 TeV was achieved 22 minutes later, at 2:34 a.m.
Two final steps were then still required to reach stable beams for physics: the “squeeze” and the “adjust”. During the squeeze, the beams are focussed by powerful quadrupole magnets (the inner triplets) located on either side of the experiments. In the adjust step, the focussed beams are carefully steered in the experiments to ensure optimal overlap at the collision points, thereby maximising the collision rate.
At 2:53 a.m., both steps were completed and stable beams were declared, signalling to the experiments that data taking for physics could start.
Three fills with 1200 bunches, totalling 20 hours of stable beams, were completed, meeting the necessary conditions to move to the next step of the intensity ramp-up. As I write, the first fill with 1800 bunches has just started. Once the same conditions have been met, the final step will be taken to reach 2460 bunches per beam, the LHC’s planned filling scheme for luminosity production during the 2025 run. If all goes according to plan, the 2460 bunches should already be circulating in the LHC when you read this report. I invite you to check LHC page 1… Are we on schedule?
On the injectors side, fixed-target physics is progressing well, with good overall beam availability, while preparations for the upcoming oxygen and neon ion runs – we will indeed also see neon ions in the machines this year! – are well under way. Oxygen and neon runs in the LHC and oxygen-only runs in the SPS North Area are scheduled for July.
The Linac3 source, typically used to produce lead ions, has been reconfigured to deliver oxygen ions to the LEIR machine. LEIR already successfully accelerated and transferred the oxygen ions to the PS earlier this week. The SPS is scheduled to receive oxygen ions on 10 June to begin the set-up operations of the machine and beam, with the goal of delivering the oxygen ions to the LHC as of 29 June. A dedicated four-day physics run with oxygen ions is planned from 3 to 6 July.
On 7 July, immediately after the oxygen ion run, the entire chain (Linac3, LEIR, PS, SPS and LHC) will switch to neon ions for a one-day run, before transitioning back to protons. Linac3 and LEIR have already proven themselves able to switch between the two species in a matter of hours. Next week, the PS too will test switching between oxygen and neon.