The High-Luminosity Large Hadron Collider (HL-LHC), a major upgrade to the world’s most powerful particle accelerator, is moving closer to reality as engineers at CERN begin testing a full section of the new system.
Featuring cutting-edge components developed at the United States Department of Energy’s Fermilab, the project aims to supercharge particle collision experiments and unlock rare physical phenomena when it comes online in the early 2030s.
With cutting-edge technology from the US and Europe working in unison, the upgrade aims to deliver ten times more collision data, opening the door to discoveries that could reshape our understanding of the Universe.
Boosting the world’s most powerful collider
The High-Luminosity Large Hadron Collider will increase the collider’s data collection capacity by an order of magnitude, allowing scientists to probe deeper into the fundamental laws of nature.
This leap in performance hinges on revolutionary new magnets, cryogenics, and beam-focusing technologies designed to pack more protons into tighter, higher-energy beams.
But before these components are installed 100 meters underground in the 27-kilometre LHC tunnel, they must undergo a critical ‘string test’ – a real-world trial of 100 meters of interconnected accelerator hardware.
This test is designed to ensure every part works together seamlessly under the extreme conditions of high-energy physics.
The string test: A dress rehearsal for the HL-LHC
The current phase at CERN replicates the section of the collider positioned to the left of the Compact Muon Solenoid (CMS) experiment.
All magnets, power systems, and cooling units are connected and operated as they would be in the final machine, only at a smaller scale.
This test goes beyond evaluating individual performance; it verifies the collective behaviour of the magnets and supporting systems when linked as a single chain.
Engineers will cool the entire section to 1.8 Kelvin (just 1.8 degrees above absolute zero) and power it to a staggering 17,300 amps, equivalent to a continuous bolt of lightning coursing through the magnets.
Fermilab’s cutting-edge contribution
Among the hardware on debut are four state-of-the-art quadrupole accelerator magnets built at Fermilab.
Each weighs 25 tonnes and incorporates coils made from niobium-three-tin, a superconducting material never before used in an operating particle accelerator.
This innovation marks a leap from the LHC’s existing niobium-titanium magnets, which produce fields up to 8 tesla.
Niobium-three-tin magnets can reach magnetic fields about 50% higher, enabling the HL-LHC to compress twice as many protons into a smaller beam volume – a vital step for achieving high luminosity.
The trade-off is complexity: niobium-three-tin is brittle and requires intense heat treatment to achieve superconductivity. Developing these magnets took decades of collaboration between US and European scientists.
A transatlantic partnership decades in the making
The origins of the HL-LHC’s breakthrough technology trace back to the late 2000s, when US teams began experimenting with niobium-three-tin while CERN was still building the original collider.
Engineers on both sides of the Atlantic exchanged ideas in marathon video calls, often working across late-night and early-morning schedules to refine designs.
This collaboration was so close that magnets now contain coils made interchangeably by Fermilab and CERN, a testament to the harmonised engineering effort.
Final checks before installation
With the magnets now connected, CERN engineers are pressure-testing the system before beginning cryogenic cooling.
Once the chain reaches operational temperature, they will ramp up the current to full strength, validating the magnets’ ability to operate continuously under extreme conditions.
Passing this test will clear the way for the installation of the HL-LHC magnets around the collision points, marking the final stretch toward a more powerful LHC.
When operational in the early 2030s, the upgraded collider will dramatically expand humanity’s ability to explore the subatomic world, pushing the boundaries of physics into uncharted territory.