Cryogenic Distribution Line, Demineralised Water System, Circuit Disconnector Boxes... The HL-LHC IT String is taking shape

With its first major equipment now in place and infrastructure nearly installed, HL-LHC’s test bed is on track to start operation in 2024.



Figure 1: WP16 and WP6B teams next to the installed Circuit Disconnector Boxes.

As mentioned on other occasions, the HL-LHC IT String is a key milestone for the High Luminosity LHC (HL-LHC). It will enable the project to test the collective behaviour of some of the major components which have been designed for the new era of the accelerator. State-of-the-art technologies and operating schemes (in terms of cooling, powering, and protection of Inner Triplet (IT) magnets and circuits) will prove their importance in this test stand.

The HL-LHC IT String is being installed in SM18, in vicinity of the superconducting magnet test benches. Its operating area is clearly delimited by the pale blue paint on the floor. Several accomplishments have taken place in 2022, which will help start the operation phase in 2024.

Figure 2: The SQXL, installed in SM18 to serve the HL-LHC IT String.

The first important milestone has been the completion of the Cryogenic Distribution Line (SQXL) installation. This cryogenic bayonet will supply liquid helium to the inner triplet magnets and cold powering equipment. The SQXL will be fully commissioned in 2023, after being pressure-tested and operated under cryogenic temperature. For the purpose of commissioning, a dedicated cabling campaign to connect the SQXL (sensors, pumps, valves, etc.) to the cryogenic control racks has taken place.

.Figure 3: The Water Distribution System designed for the HL-LHC IT String.

Furthermore, the Demineralised Water Distribution System – which is a closed-loop circuit connected to a water station in P18 site – has been installed. It will provide demineralised water cooling to different users of the test stand – such as Power Converters (PCs), copper high current Busbars (BBs) and Water‑Cooled Cables (WCCs) – to keep the equipment running at adequate temperatures. The system comprises a main water channel, and ramifications to serve different equipment. The demineralised water network includes flowmeters, valves, pressure indicators, flow switches, etc. Special mention must be made of the branch installed for the WCC segments belonging to the RD1 circuit. It will allow one to test several water supply configurations and select the most suitable option for the machine. The end connections – made with flexible pipes – are expected for 2023, once all the equipment is installed atop the metallic platform.

Other important components already in place include the Circuit Disconnector Boxes (CDBs), which are the first equipment delivered by a WP – other than WP16 – to the HL-LHC IT String. They guarantee proper interfacing between the warm and cold powering systems, while providing safety measures. They also facilitate access for interventions, such as regular electrical compliance checks of circuits powered through DFH cold feedboxes. The three CDB models foreseen are the ones designed for 18 kA, 2 kA and 0.6 kA currents. It is worth remembering that the CDBs are a new development for the HL-LHC era and the HL-LHC IT String is where they will be tested for the first time as part of a circuit.

Finally, the WCCs have recently been installed on dedicated cable trays – attached to the metallic platform – and connected to the CDBs. These copper cables have cross sections of 500 mm2 (2 kA circuits) and 1300 mm2 (2 cables per polarity for the 14 kA and 18 kA circuits). They will be used at room temperature, connecting the PCs to the CDBs.

Demineralised water will flow inside the WCC hose – in direct contact with the bare conductor strands – to evacuate the heat generated by the Joule effect. This configuration allows transporting of high currents in confined spaces, where other type of cooling (e.g. air-cooling) would be impossible or less efficient. The same strategy will be applied in the HL-LHC. It is to be noted that a solution based on air-cooled cables would have increased the complexity of the installation in the HL-LHC technical galleries, since the heat load would have had to be evacuated by HVAC units.

Figure 4: WCCs connected to CDBs in the HL-LHC IT String.

In terms of schedule, the WCCs were part of the critical path last year – however, mountains were moved to ensure their timely delivery. As a result, they are already in place (as shown on Fig. 4) and awaiting connection to the PCs in 2023.

Apart from the on-site activities, the IT String Day II was conducted in September 2022 to assess project advancement, as well as to start preparing for 2023 installations. All the involved groups and WPs presented their primary milestones, activities and constraints – such as studies related to the magnet interconnection process and cold powering equipment installation.

Finally, in present times, it is of upmost importance to ponder all aspects related to the sustainability of the project. In that sense, most HL-LHC IT String components will become machine spares after their operation in the test stand. Options for other infrastructure components have been proposed (e.g., recycling the steel used for the metallic structure and the copper comprising the WCCs).

Find out more about the HL-LHC IT String: