The HL-LHC IT String is a major, intermediate milestone for the HL-LHC project ahead of the installation of the first cold powering systems in the LHC tunnel during LS3. The IT String will enable testing of the collective behavior of many new key hardware systems designed for the new era of the High Luminosity LHC. New technologies and operating schemes (in terms of cryogenics, powering and protection of the IT magnets and circuits) will for a first time demonstrate their functionality as a fully integrated system in the IT String.

All necessary equipment will be installed in an area of SM18 dedicated to the IT String (see Figure 1). The successful completion of the test program and the experience gained during the IT String will be an important step for the project to ensure the smooth installation and commissioning of the equipment in their final location inside the tunnel. The WP16 coordination team and all project stakeholders are moving ahead to install and interconnect all the components in compliance with the WP16 master schedule.

The IT String planning is therefore continually assessed, so as to establish an optimal installation sequence based on the availability dates of key components. The current plan foresees the installation of several components before the end of this year still (i.e. the Circuit Disconnector Boxes and the water-cooled cables). The installation and interconnection of the cold powering system and the 19 magnets that will be delivered will follow in 2023.

Up to now, the installation of the test stand in SM18 advances at a rather remarkable pace. In the space of only one year, from mid-2021 to mid-2022, many activities have been completed:

• The IT String area has been cleaned and painted, to improve visibility and allow easy marking of equipment positions on the floor.
• The metallic platform has been installed and it is almost ready to receive components. The passage structure for routing the SC Link all the way to the DFX is also in place.
• Numerous cable trays have been placed, in accordance with integration drawings, for routing all cables related to AC Powering, DC Powering, Signals, Communications, etc. 
• Many of the racks have been positioned on the ground floor of the IT String area and they are ready to house the electronics inside.
• Cryogenic Infrastructure and Proximity Cryogenics equipment are installed, pending the installation of the SQXL to start the full commissioning of the system.

Apart from the equipment itself, the meeting room in SM18 is being refurbished to accommodate the future control room of the IT String. The work is nearing completion and includes, among others, the change of the floor, the furniture, the modification of the lighting configuration and the opening of two large windows to equip the room with natural light and fresh air.

The upcoming months will continue to be very interesting, whereas special attention will be given to the installation of the SQXL along the magnet line, the installation of the Demineralised Water Distribution System, the installation of the water-cooled cables and their connection to the Circuit Disconnector Boxes.

Other essential equipment, such as the SC Link, DFHX, DFX or the IT magnets will have to wait until next year to seize their place within the String.

In parallel to the installation activities, discussions are ongoing on a regular basis, to draw up specific test procedures for the IT String Validation Program as well as to start preparation of the operational tools required. The baseline of this validation program, containing a description of the tests to be performed and a detailed sequence of execution, has already been documented and approved.

Finally, as personnel and equipment safety is an important concern in the heavily frequented test area of SM18, a complete risk assessment is being performed for the HL-LHC IT String installation and operation. Topics such as dedicated uninterruptible power supplies for the IT String, emergency exits, location of fire extinguishers and AUG buttons, safe distances to the equipment or access to the different IT String zones are being addressed.