On 20 April 2026, another important milestone was reached for the High-Luminosity Large Hadron Collider (HiLumi LHC) project, with the start of the electrical powering of the 95-metre-long test stand called the Inner Triplet String (IT String). Following its successful cryogenic cooldown to 1.9 K (‑271.3 °C) a few weeks ago, it will be powered up progressively, circuit by circuit, over the next few weeks.
The IT String is a full-scale test stand that replicates an entire region of the future HiLumi LHC, set to enter into operation in 2030. This ground-breaking accelerator will increase the number of particle collisions (called "luminosity") by a factor of ten, vastly increasing the volume of physics data available to researchers. Transforming the LHC into a high-luminosity accelerator requires a four-year intensive programme of work that will start this summer. During this time, innovative technologies will be installed in the LHC tunnel, including novel magnet systems - the inner triplet beam-focusing magnets - and the associated complex infrastructure. The test stand is designed to validate this major set of key technologies for the HiLumi LHC.
The IT String brings together all the systems required to operate under nominal conditions, including, of course, the inner triplet magnets, but also powering equipment, in particular an innovative superconducting link, cryogenics, protection systems, the magnet alignment infrastructure and other auxiliary systems. Together, these components form 17 circuits.
"The IT String is the result of many years of research and development and incorporates a wealth of technological innovations. Finally reaching the point where, step by step, each of the complete circuits is switched on marks a decisive milestone for CERN's HiLumi LHC and for all the teams involved in the project," explains Markus Zerlauth, HiLumi LHC Project Leader.
The High Order Corrector (HOC) circuits include the very first components to be powered. They are designed to correct the beam parameters and the magnetic field errors of the quadrupole magnets in the inner triplet circuits. The powering will then be carried out progressively, following the same sequence as that planned for the accelerator hardware commissioning of the final HiLumi LHC machine. Initial steps will focus on verification of the powering infrastructure and protection systems, before gradual advancement to the more complex circuits. In the coming weeks, the programme will integrate more components and reach higher levels of current. This staged approach will see the powering of the main inner triplet magnets in June and of the whole installation later this summer, marking a key step in the validation of the full system under operational conditions.
"This project, up to this stage, has been an exciting journey, bringing together members from all departments at CERN. The installation was not without challenges, but each difficulty provided valuable lessons that have since been integrated into improvements of the design and installation procedures," says Marta Bajko, head of the IT String project. "One of the major issues encountered during installation of the IT String was a leak caused by a component that required further optimisation. Addressing this problem led to a six-month programme of work, which was successfully completed on schedule, allowing us to start testing the powering this week."
The successful execution of this programme will demonstrate the readiness of the HiLumi LHC inner triplet systems and their associated technologies, paving the way for their installation in the LHC during the imminent Long Shutdown 3 and for the subsequent exciting era of high-luminosity physics.
