CERN Lights Up the Magnets of the Future: Here's What Will Change for the World's Largest Accelerator

The CERN has reached a new milestone in the development of the High-Luminosity Large Hadron Collider (HL-LHC), the upgrade program of the world's largest particle accelerator set to go live in 2030. At the IT String (Inner Triplet String) testing facility, the new generation of superconducting quadrupole magnets has successfully achieved the operational nominal current of 16,230 amperes, completing a crucial phase of the validation process for the infrastructure.

This result represents a key step towards the future configuration of the accelerator, designed to significantly increase the luminosity of the Large Hadron Collider – which is currently shut down to prepare for the upgrade. A greater number of collisions between protons will indeed allow for the collection of larger datasets, improving the accuracy of experimental measurements and increasing the chances of observing extremely rare phenomena, including any effects that go beyond the Standard Model of particle physics.

The new magnets constitute a significant evolution over the current niobium-titanium Inner Triplet magnets. The new superconducting coils utilize niobium-tin (Nb3Sn), a material that enables reaching magnetic fields of 11.3 tesla, about 35% higher than the generation currently installed in the LHC. In parallel, the useful internal diameter of the magnets has also been increased from 70 to 150 millimeters, a feature that allows for more precise focusing of the proton beams before collision, thus increasing the number of produced interactions.

One of the most relevant aspects of the tests relates to the fact that the magnets reached the nominal current without any quench, which is the transition from superconductivity to normal conductive state. Superconducting magnets typically require a training period, during which they undergo repeated powering cycles with progressively increasing currents. In the early stages, quenches are common, usually caused by small internal mechanical instabilities that are gradually eliminated with successive tests.

The observed behavior also demonstrates a strong capacity of the magnets to retain the results of the training, a property known as “memory.” As explained by Susana Izquierdo Bermudez, head of the Large Magnet Facility at CERN, good memory in magnets is a fundamental requirement as it reduces commissioning times, limits the consumption of the cryogenic plant, and helps contain potential operational delays.

The testing campaign covered the entire IT String infrastructure. All 17 electrical circuits were successfully brought to their respective operational currents. Even the separation dipole, which will be responsible for moving the two particle beams apart after collision in the future HL-LHC, reached the expected current after a limited number of quenches during training, while the correction magnet circuits met the objectives both during individual operation and in combined operation.

The tests also verified the proper functioning of the magnets' protection system, designed to safely dissipate the stored energy in the event of an anomaly. During testing, the system managed up to 38 megajoules of magnetic energy, transferring it to the bath of liquid helium that keeps the magnets at the operational temperature of 1.9 kelvin, which is about -271 °C.

The collected data will now be analyzed to delve deeper into the interaction between all involved subsystems, including cryogenic power supply, power converters, detection and quench protection systems, vacuum, controls, and alignment.

The activities are not concluded. In the coming months, further tests will be conducted dedicated to the study of superconducting circuits, operational cycles of the accelerator, electromagnetic couplings, and alignment procedures. Following a temporary return to room temperature and a new cooling of the facility, a second test campaign will kick off in September, aiming to validate commissioning procedures, verify analysis tools, and demonstrate the reproducibility of the integrated system's performance under conditions increasingly close to those of the future High-Luminosity LHC.