The High Luminosity (HL) version of the Large Hadron Collider (LHC) is at the top of the top priorities of the CERN management and of High Energy Physics all over the globe including the U.S. P5 recommendations and the European strategy report. As we are seeing during Run 3, the LHC in its present configuration has run out of steam. To make the running worthwhile we either have to increase the energy, which unfortunately we cannot as the magnet run close to their breaking point already, or increase the beam intensity (luminosity) to accumulate substantially more data than taken so far in short amount of time. While many of us focus on the upgrade of the detectors that is moving at a furious pace, the upgrades to the accelerator are often taken for granted. It is encouraging to hear that last week CERN announced that it has reached a critical milestone.
The recent start of the cryogenic cooldown for the 95-meter-long Inner Triplet String test stand marks a pivotal achievement for CERN and the High-Luminosity LHC project. By cooling this full-scale replica to a temperature of 1.9 K, engineers are finally able to validate the collective performance of innovative technologies that have previously only been tested in isolation. This test stand specifically mimics the underground configuration of the new beam-focusing magnets, which are made from a niobium-tin superconducting compound. These magnets are designed to produce significantly higher magnetic fields than those currently used in the LHC, and the successful operation of the IT String will ensure that the integration and power systems are fully optimized before the actual hardware is installed during the upcoming four-year long shutdown.
The broader goal of the HL-LHC project is to transform the existing accelerator into a machine capable of increasing its luminosity the number of particle collisions by a factor of ten. By tilting proton beams with superconducting crab cavities and utilizing high-temperature superconducting transfer lines, the project aims to push the boundaries of what is technically achievable in a proton accelerator. This massive increase in the volume of physics data will allow researchers, for example to study the Higgs boson with a level of precision that was previously impossible. A primary scientific objective of this upgrade is to measure how the Higgs boson interacts with itself, a feature that is precisely predicted but has never been observed and that is a fundamental property of the standard model.