In the Large Hadron Collider (LHC), counter-rotating beams of protons travel in separate chambers under high vacuum to avoid scattering with gas molecules. At four places around the 27-km ring, the beams enter a single chamber, where they collide. To ensure that particles emerging from the high-energy collisions pass into the ALICE, ATLAS, CMS and LHCb detectors with minimal disturbance, the experiments’ vacuum chambers must be as transparent as possible to radiation, placing high demands on materials and production.
The sole material suitable for the beam pipes at the heart of the LHC experiments is beryllium — a substance used in only few other domains, such as the aerospace industry. Its low atomic number (Z = 4) leads to minimal interaction with high-energy particles, reducing scattering and energy loss. The only solid element with a lower atomic number is lithium (Z = 3), but it cannot be used as it oxidizes rapidly and reacts violently with moisture, producing flammable hydrogen gas. Despite being less dense than aluminium, beryllium is six times stronger than steel, and can withstand the mechanical stresses and thermal loads encountered during collider operations. Beryllium also has good thermal conductivity, which helps dissipate the heat generated during beam collisions, preventing the beam pipe from overheating.
But beryllium also has drawbacks. It is expensive to procure as it comes in the form of a powder that must be compressed at very high pressure to obtain metal rods, and as beryllium is toxic, all manufacturing steps require strict safety procedures.
By bringing beam-pipe production in-house, CERN will acquire unique expertise
The last supplier worldwide able to machine and weld beryllium beam pipes within the strict tolerances required by the LHC experiments decided to discontinue their production in 2023. Given the need for multiple new beam pipes as part of the forthcoming high-luminosity upgrade to the LHC (HL-LHC), CERN has decided to build a new facility to manufacture vacuum pipes on site, including parts made of beryllium. A 650 m2 workshop is scheduled to begin operations on CERN’s Prévessin site next year.
By insourcing beryllium beam-pipe production, CERN will gain direct control of the manufacturing process, allowing stricter quality assurance and greater flexibility to meet changing experimental requirements. The new facility will include several spaces to perform metallurgical analysis, machining of components, surface treatments, final assembly by electron-beam welding, and quality control steps such as metrology and non-destructive tests. As soon as beryllium beampipes are fabricated, they will follow the usual steps for ultra-high vacuum conditioning that are already available in CERN’s facilities. These include helium leak tests, non-evaporable-getter thin-film coatings, the installation of bakeout equipment, and final vacuum assessments.
Once the new workshop is operational, the validation of the different manufacturing processes will continue until mid-2026. Production will then begin for new beam pipes for the ALICE, ATLAS and CMS experiments in time for the HL-LHC, as each experiment will replace their pixel tracker – the sub-detector closest to the beam – and therefore require a new vacuum chamber. With stricter manufacturing requirements, never accomplishment before now, and a conical section designed to maximise transparency in the forward regions where particles pass through at smaller angles, ALICE’s vacuum chamber will pose a particular challenge. Together totalling 21 m in length, the first three beam pipes to be constructed at CERN will be installed in the detectors during the LHC’s Long Shutdown 3 from 2027 to 2028.
By bringing beam-pipe production in-house, CERN will acquire unique expertise that will be useful not only for the HL-LHC experiments, but also for future projects and other accelerators around the world, and preserve a fundamental technology for experimental beam pipes.
