ATLAS is the largest general-purpose particle detector experiment at the Large Hadron Collider (LHC). It is designed to investigate fundamental physics, from studying the Higgs boson to exploring particle physics theories beyond the Standard Model.
This latest upgrade will ensure that ATLAS can handle the significant increase in collisions expected from the High-Luminosity LHC project, replacing the experiment's Inner Detector with the newer ITk.
Known as strip staves, the ITk detector’s 392 sensor assemblies will detect the sub-atomic particles produced when two high-energy beams of protons smash into each other in the Collider.
Around 200 of these staves will be assembled in Technology’s Detector Integration Facility, each with 28 detectors connected using 150,000 wire bonds – tiny strips of aluminium measuring just 25 µm wide. That’s about the size of a white blood cell.
Eventually, this specialised detector technology will be shipped to CERN’s SR1 cleanroom and installed in the ITk strip barrel. This involves the careful insertion of the staves into one of four carbon-fibre cylinders without damaging either component.
With each stave worth £150,000, any mistakes made during the insertion are costly, raising the question: how do you safely install £60M worth of detector technology?
The answer? A carefully engineered insertion mechanism.
Precision engineering for a high-stakes job
Graduates, Anmol and Harry, working in the detector barrel
Developed by the department’s Project Engineering Group, this mechanism features two ‘arms’ connected to a carriage in which a stave can be placed.
These arms can rotate 360 degrees to access the entire circumference of the detector barrel, before extending and tilting to place the staves – which, once in their final position, will overlap like tiles on a roof.
The mechanism requires two operators on either end to turn the handwheels that rotate the carriage and uses an alignment system, with magnets and sensors, to carefully place the staves without touching the carbon-fibre cylinders surrounding them.
Installing each stave into the barrel is like threading an extremely small needle; operators have just millimetres of clearance to work with.
Making this challenging task even more difficult, they must work while balancing on two small platforms, so that they don’t damage the bottom of the barrel.
Fortunately, the mechanism was designed with these constraints in mind, with several safety features ensuring that operator error or mechanical failure does not compromise the project.
This includes a braking system connected to a dead man’s switch that automatically stops the carriage’s rotation if the operator releases the button.
Using a completely analogue approach when designing the mechanism, with no automatic functions, ensures that machine error does not damage any delicate and expensive components. However, it also means that proper training is vital.
From concept to commissioning
(Left to right, front to back) The insertion mechanism team: Anmol, Harry, Charles, Dave, Steve, and Rashid.
Between April and June 2025, Technology staff travelled to CERN to deploy the insertion mechanism and demonstrate its capabilities by successfully installing a prototype stave.
Soon, the team will return to fully commission this technology, refine the operation process, and train CERN colleagues in its safe use.
This delivery represents the culmination of years of hard work from Technology’s Project Engineering Group (PEG), working closely with collaborators from the Czech Technical University in Prague on the design and testing of the system.
Charles Evans, Senior Mechanical Engineer in Technology’s Project Engineering team, shared:
“Working on a large-scale international programme like ATLAS for 10 years, collaborating with people from so many different fields of expertise towards a common goal of epic proportions, has been a gratifying and enlightening experience.
“Within PEG, we have many skilled engineers who have contributed to this success of building a system that can safely handle the strip staves and allow the UK to deliver a key contribution to the upgrade project, enabling the construction of the new strip barrel detector assembly."
Alongside the development of the insertion mechanism and the production of staves and their individual sensors, Technology teams have contributed to:
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The design of the barrel structure, which holds the staves in position.
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The design and construction of the service assemblies that supply data, power, and high-pressure cooling to the staves, maintaining a consistent -30 °C.
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The design of trigger electronics hardware and firmware, ensuring that interesting physics events are selected for further analysis.
Once each stave is inserted and tested, the service modules will be installed, providing the next engineering challenge: carefully welding nearly 2,000 connections to the delicate staves and working in the extremely narrow spaces between sub-detectors.
Written by Cat Lewin-Williams and Charles Evans
