This summer, as the temperature climbed ever higher at CERN, the TE-CRG team began to work with its coolest equipment by launching the first commissioning phase of the cryogenic system of the HL-LHC IT String. This installation is the future test stand that will be used to validate the collective behaviour of the Inner Triplet (IT) magnets and circuits of the High Luminosity LHC (HL-LHC), provide up front information about the operational behaviour of the IT magnet system and thus help to prepare its commissioning in the LHC tunnel.

Conducted within approximately three weeks in July, this first phase, which was performed without magnets, aimed to operate the system in the conditions planned for the future operation, and to determine the operational parameters and performance of the system. The commissioning started with a cooldown, which lasted 10 days, with five days of active temperature transients. Several inspections were performed at stable temperature and pressure conditions (at 250 K, 90 K and 50 K) and confirmed the absence of leaks and of apparent mechanical issues. It was also confirmed that the instrumentation and that the main control loops are providing the required functionalities. The cold compressor unit (CCU), which will be needed for the operation of the IT String, was also tested and reached its nominal operating conditions.

What are the next steps? The second commissioning phase (still in standalone mode) is planned in the coming months and will be dedicated to further study the performance of the cryogenic system and to refine its operational parameters. The last phase of the commissioning will be performed after connecting the magnets as well as the cold powering and will lead to the start of the IT String operation. This staged approach allows to anticipate and solve any potential issues with the cryogenic system, thus helping to save time and to ensure a more efficient test campaign with the IT magnets.

This first cooldown is a significant milestone in the preparation for the operation of the HL-LHC IT String. The commissioning of the HL-LHC IT String started earlier this year (highlighted in the earlier article of Accelerating News).  The cryogenic system, which was installed between 2020 and 2023, consists of a cryogenic distribution line (SQXL), which resembles the future cryogenic distribution line (QXL) in the HL-LHC tunnel, a Proximity Cryogenic Distribution System (PCDS), which connects the SQXL to the SM18 infrastructure, a 6 kW @ 4.5 K helium refrigerator, a cold compressor unit (CCU) of a 18 g/s pumping capacity at 10 mbar, warm pumping units, and the data acquisition and control systems. The cryogenic system will also include a warm quench buffer and a gas management system for the cold powering, which will be installed in the future.