CERN Begins Historic Magnet Replacement at Large Hadron Collider

A Generation of Magnets Retires After Two Decades

The European Organization for Nuclear Research (CERN) has formally begun removing 28 superconducting magnets from the Large Hadron Collider, marking the end of nearly two decades of operational service for hardware installed between 2005 and 2007. The removal process commenced on September 7 as part of the third long shutdown (LS3), with CERN Director-General Mark Thomson present at the ATLAS experiment site to commemorate the milestone. The magnets being retired include crucial inner triplet systems—groups of three quadrupole magnets positioned on both sides of the collider's four main experiments.

These inner triplet magnets have played an essential role throughout the LHC's operational history by focusing particle beams to their tightest possible compression just before collision. The degree of beam compression directly determines collision frequency, a measure known as luminosity. Higher luminosity translates to more collision events per unit time, providing researchers with substantially more data for analysis. After nearly twenty years of reliable performance, this generation of magnets will be supplanted by significantly more powerful successors designed for the High-Luminosity LHC (HiLumi LHC) initiative.

Technological Leap: A 40% Increase in Magnetic Field Strength

The replacement magnets represent a substantial technological advancement over their predecessors. The current LHC inner triplets rely on niobium-titanium superconducting coils, but the new generation employs niobium-tin superconducting technology. This material shift enables the upgraded magnets to generate magnetic fields reaching 11.3 tesla—approximately 40 percent stronger than the 8 tesla fields produced by the existing magnets. The enhanced field strength will deliver dramatically increased collision rates at the ATLAS and CMS experiments, where such intensity is particularly valuable for discovering rare particle interactions.

Jean-Philippe Tock, heading the LS3 Coordination Team, outlined the magnitude of the undertaking: the installation will require 16 cryostats and 28 cryo-assemblies to be positioned throughout the tunnel. The first of the new quadrupole magnets is expected to arrive at the collider's underground tunnel in early 2029, representing the completion of years of intensive research and engineering development dedicated to pushing the boundaries of particle detector capability.

Differentiated Upgrade Strategy Across Four Experiments

The replacement initiative follows a strategic approach tailored to the distinct operational requirements of the LHC's four major detector experiments. The ATLAS and CMS collaborations will receive entirely new inner triplet systems optimized for maximum luminosity enhancement, as these experiments benefit most from the increased collision rates. By contrast, the ALICE and LCb experiments operate under different physics frameworks and pursue distinct scientific programs that do not demand the same instantaneous luminosity increases. Consequently, their existing inner triplet magnets remain in place, though they will still undergo upgrades to capitalize on the overall luminosity improvements across the entire facility.

A Massive Infrastructure Undertaking

The scale of this replacement operation cannot be overstated. The 27-kilometer circumference LHC contains thousands of magnets of various specialized types—dipoles, quadrupoles, sextupoles, octupoles, and decapoles—each performing distinct roles in steering and controlling the particle beams with precision. The removal and replacement of 28 superconducting magnets along with their associated infrastructure represents one of the most complex maintenance operations in the facility's history. The project team must carefully extract decades-old equipment while preparing the tunnel to receive an entirely new generation of superconducting systems designed to operate at significantly higher performance levels. This transition symbolizes a handover from one era of particle physics innovation to the next, positioning CERN to pursue scientific discoveries requiring collision data at unprecedented intensity levels throughout the coming decade of high-luminosity operations.