The operation of the IT String represents a significant milestone for the HL-LHC Project as it is where many state-of-the-art technologies developed for the HL-LHC will operate collectively for the first time. The installation and commissioning of this unique test stand have seen relevant achievements in recent months.
Cryogenic system tests
The IT String cryogenic system supplying superfluid helium to the magnets is composed of the IT String Cryogenic Line (SQXL) and the Proximity Cryogenic Distribution System (PCDS) which connects the SQXL to the building infrastructure. The commissioning of the cryogenic system is divided into two main phases; Phase 1, conducted without the magnets, and Phase 2, conducted with the magnets. Before Phase 1, a leak tightness verification of the helium and vacuum volumes was performed, resulting in the detection and repair of a few leaks.
The cryogenic system has undergone two cooldown phases, Phases 1A and 1B (figure 1). Phase 1A validated the mechanical integrity of the system, with no thermal contraction issues identified. These tests also facilitated the optimisation of the cooling process. However, slightly higher heat loads than anticipated were observed in the cryogenic lines. Phase 1B focused on refining measurements, tuning the automatic control algorithms, and achieving the required performance. During this phase, heat loads were further assessed, leading to the discovery of a contact point between one of the lines and the surrounding enclosure, triggering the subsequent repair.
Short-circuit tests
An important milestone for the IT String was achieved in 2023 and 2024 with the installation and successful validation of the complete warm powering system. This system includes power converters, circuit disconnector boxes, energy extraction systems, ElQA patch panels, air-cooled cables, water-cooled cables, and water-cooled bus bars. Initially, each component was tested individually, undergoing different tests such as pressure tests, voltage withstand tests, operational fault mechanism checks and functionality verification. Following individual testing, the warm powering system was connected and powered to ultimate current in a short circuit configuration at the warm-to-cold transition extremities, as illustrated in figure 2.
The steps executed during short-circuit tests included the validation of interlocks, the tuning of control loops, the discharge of the energy extraction system and power converter, and the 8-hour heat run test for thermal validation. This last test required the simultaneous powering of all circuits at ultimate current for 8 hours, as shown in figure 3.
Cold powering system
Following the successful individual testing of the cold powering system in the SM18 F2 bench, the next step is its installation in the IT String, scheduled for Q3 2024. The sequence for this activity has been meticulously planned. It involves raising the DFHX and the SC-link onto the metallic platform in SM18 using two overhead cranes. Special tools, including a lifting frame with a drum and motor for controlled unspooling of the SC-link, have been designed and procured for this purpose. Scaffolding around the IT String area will assist in positioning and provide operator access during installation. Transport tests using the lifting frame have been successfully conducted (see figure 4). Immediately after the DFHX installation, work will commence on installing proximity equipment, connecting cables, and pipes, followed by the DFX assembly.
