The SM18 test facility continues to play a central role in validating critical components for the HL-LHC Project. Currently all upgrades of the various test stations have been completed, including a second cold box providing helium for the IT String, a large update campaign for magnet test benches, new instrumentation hardware with quench antenna and magnetic measurement shafts.
With the acceleration of hardware delivery and integration milestones across multiple work packages (WPs) a consolidated mid-term testing strategy is essential to align resources, scheduling, and technical priorities. To this extent, a technical coordination of the SM18 test facility was set up and is put in place to optimise the shared resources, especially when it comes to the cryogenic capacity shared between the users in the building.
For HL-LHC WP4 (Crab Cavities), out of the ten series DQW dressed Crab Cavities, four have been successfully tested and qualified. In the coming months, efforts will be concentrated on validating the remaining six series DQW cavities provided by German industry. This will require a minimum of 17 cold RF tests in a vertical cryostat to cover the bare, jacketed and dressed configurations during the 2025-2026 period.
In parallel, the mitigation plan for the RFD cavities, which was launched at the beginning of this year, will require an additional 5 cavity tests. CERN will cryostat one DQW cryomodule, as originally planned, and possibly one additional RFD cryomodule as part of a strategy implemented to mitigate schedule risks with the timely delivery of all cryomodules for installation during LS3. These activities are expected to take place between 2026 and 2028.
Looking ahead, the testing of series cryomodules (both DQW and RFD) in the horizontal bunker is scheduled to begin in the first quarter of 2026 and will continue through to the end of 2029, with a total of ten cryomodules to be tested during this period.
Figure 1. DQW dressed cavity during installation on the vertical cryostat. Nuria Valverde Alonso / CERN
For WP3 (IR Magnets), the vertical testing of eighteen out of twenty corrector magnets needed for installation in the cold masses has been completed. On the horizontal benches the testing of the Q2 cryo-assemblies is in full swing with the fifth cryo-assembly on the bench, with eight needed to be installed during LS3 in total. In parallel, the D1, D2 and Corrector Package (CP) cold masses are tested. The choice to have one optimised test bench for each magnet type should help to efficiently qualify the magnets during the peak test load which is expected to occur until the end of 2026.
For WP6A (Cold Powering), a dedicated test bench for the Superconducting Link (SC-link) systems including current leads and interfaces is fully operational and allows validation of cryogenic and electrical performance, in addition to insulation integrity. The test is performed with the same power converters as for the Q2 cryo-assemblies, but with fully optimised test plans. Following the successful validation of the first prototype cold powering system, the first series system for an inner triplet configuration is being prepared for cold tests.
Figure 2. Q2 magnet in test next to a Superconducting Link in SM18. Mike Struik / CERN
As the main system integration platform for cross-work package verification, WP16 (IT String) combines tested components also from WP3, WP6a, and WP6b (warm powering) and functional testing of powering, magnet protection, cryogenic systems and the fully remote alignment system will simulate nominal operational conditions. Preparatory testing throughout 2025 will ensure that all elements meet the technical and operational requirements for full cryogenic and powering tests scheduled as of autumn 2025.
The period after the technical stop in summer 2025 and throughout 2026 is expected to be the most challenging period for all users in SM18, with important deliverables to be validated for all WPs for the HL-LHC. The cryogenics team and all SM18 users are ready to take on this challenge in a coordinated effort.
Figure 3. Test planning in SM18. CERN.