The SM18 building at CERN has recently become the home of a new HL-LHC infrastructure that will be used in the coming years. It is none other than the new metallic structure for the HL-LHC IT String. The HL-LHC IT String is the future test stand that will validate the collective behavior of the Inner Triplet (IT) magnets and circuits, in conditions as close as possible to the operational ones. The HL-LHC IT String is a major, intermediate milestone for the HL-LHC project. It will as well allow the verification of systems integration, as well as anticipate a smooth hardware commissioning of the systems in the final machine environment, deeply in the underground.

The construction works of the metallic structure have been completed in September 2021. Some preparatory activities are ongoing to allow the installation of the warm and cold powering equipment. The latter include among others the distribution feedbox (DFHX), the MgB2 superconducting link, the circuit disconnector boxes (CDB) and the 18 kA Power Converters. As for the superconducting magnets working at cryogenic temperatures (1.9 K), the so-called Q1, Q2a, Q2b, Q3 and D1 will be installed underneath the structure, all along the String area.

The dimensions and shape of the structure responds to the requirements of the different equipment and respects the constraints of the building, which is shared with the Superconducting RF cavities test stands and the individual superconducting magnet test benches. With this in mind, intensive integration work had been carried out by CERN’s Engineering Department (EN), involving continuous tweaks to the structure, along with changes to the equipment design and maintainability needs.

In terms of safety, the role of the metallic platform is clear: it accommodates potentially hazardous equipment in a controlled area. The fact that the equipment is on a different level from the ground floor provides additional safety in the event of a He release or an electric arc.

From drawings to reality

Once the integration had advanced enough, the design of the structure was refined by an external Swiss design office, including load simulations and the definition of steel profiles. CERN's occupational Health & Safety and Environmental Protection Unit (HSE) then validated the design, before the procurement process could finally begin.

The Site and Civil Engineering (SCE) Department negotiated the construction of the metallic structure through a framework contract at CERN. This strategy allowed for the tendering process to be accelerated and offered more flexibility during installation, since the contractor was already on the CERN site.

The Technology Department (TE), Machine Protection and Electrical Integrity Group, String Facility section, as the owner of the structure, coordinated the different activities and stakeholders involved to deliver the structure on‑time,on‑budget and to the relevant specifications.

The work does not stop

Although the metallic structure has already been installed, the work does not stop. Various preparatory works are still underway to fully prepare the structure for the arrival of components in 2022.

Cable trays are being attached to the metallic structure to route different types of cables: AC power, signal, and DC power cables. The demineralised water distribution system will also be routed along the metallic structure and supported by its beams and pillars.

Among the tasks yet to be done, there’s still marking the position of the equipment, and cutting the platform floor in specific locations in order to allow for easier routing and connecting of cables and flexible pipes to the equipment on the platform.

Finally, an additional support frame and cable trays are to be installed on the metallic structure to support the water-cooled cables running from the power converters to the circuit disconnector boxes.

Soon, we will be able to see equipment on the platform, ready to prove their nominal performance in the orchestra of IT String components. Each equipment should play its part to successfully pass the flurry of tests foreseen in the HL-LHC IT String Validation Program.

It seems that things are moving very fast at SM18; you could say: “almost at the speed of the protons guided by HL‑LHC magnets”! We are confident in the teams’ ability to keep up this pace, so we can see the IT String operating at nominal cryogenic temperatures in 2024!