Last summer (2024), after my first year of studying mechanical engineering, I undertook an eight-week engineering internship with CERN. Funded by the Royal Academy of Engineering, my work focused on validating components for the CMS (Compact Muon Solenoid) detector tracker upgrade. Split across two locations, I spent four weeks at the University of Bath and four weeks at CERN in Geneva.

Collaborating across countries

At Bath, I performed step-stress accelerated life testing on cooling pipes using a LabVIEW-controlled pressure test rig. Although based in the UK, I collaborated closely with CERN’s team in Switzerland. I learnt to work independently and to take initiative. I taught myself how to use CT scanning and optical microscopy for root cause analysis. And I built a MATLAB App Designer tool to automate data processing and accelerate failure detection.

When I arrived at CERN, my first task was to demonstrate the rig’s setup, operation, and technical specification. I then began redesigning the rig to meet CERN’s safety standards, producing a full CAD model and parts list rated for 200 bar. This also gave me a chance to ask broader questions about the project: What is CMS? How are protons circulated? Why is carbon fibre used? What is the tracker upgrade for?

Upgrading the tracker

CMS is one of the main detectors in the Large Hadron Collider (LHC), designed to study high-energy proton-proton collisions. Protons are produced by stripping electrons from hydrogen atoms, then accelerated through a series of machines before entering the LHC. There, 144 proton batches are guided to collide using a 40 MHz clock and strong solenoidal magnets.

The tracker is the innermost part of the detector, recording the paths of charged particles just after collision. It must be lightweight and stable to avoid disrupting the particles before their energy is measured by the calorimeter. Hence, the use of carbon fibre for its high stiffness-to-weight ratio. The tracker’s silicon detectors are arranged in a conical shape to capture a wider spread of trajectories. But they generate significant heat, which makes cooling essential. The new two-phase CO₂ cooling system works like an aerosol can: a pressure drop triggers a phase change, drawing heat away.

'Visiting the CMS service cavern and the control centre at Point 5 gave me a clearer understanding of the scale and purpose of the work I was supporting.'

An opportunity to explore materials

Early on, I asked to take on extra work in composite quality assurance to deepen my understanding of materials. I performed tensile tests on carbon fibre and aluminium samples following ISO 527-4 standards and using the Zwick/Roell testXpert II system to measure dimensions, preload samples, and generate stress–strain curves. Carbon fibre showed brittle failure and a high Young’s modulus, while aluminium exhibited plastic deformation. The results confirmed the quasi-isotropic nature of the supplier’s laminates, which are now being used in the tracker upgrade.

In my third week, I assembled and validated the redesigned rig. I finalised the user manual for future use and conducted tensile tests on the titanium pipes. I also completed my CMS Technical Shifter training, which allows me to support the detector from the control room. Additionally, I learned about joining dissimilar materials through brazing. I observed induction, furnace, and electron beam brazing techniques and studied filler materials such as silver, copper, and indium.

At the end of my time at CERN, I supported an investigation into helium leak failures in a batch of titanium pipes. I collaborated with the cleaning and brazing teams to identify potential causes. These included poor surface preparation, oxide residues, and grainy filler texture. I toured CERN’s metal cleaning facilities to learn about processes such as degreasing, acid etching, and nickel plating. I also learnt why materials like zinc or silicon-based oils are banned. It's due to the risk of contaminating sensitive detector components.

CERN's supportive engineering culture

Throughout the internship, I experienced CERN’s collaborative, transparent and hands-on engineering culture. Engineers get to build and test their designs, seeing them all the way through. By asking questions and volunteering for extra responsibility, I gained experience in composites and quality assurance. These were areas I wasn’t originally meant to work in. I also had the chance to live abroad, meet people from all over the world, and contribute to an international research effort.

I’m incredibly grateful to Dr Alexander Lunt and the team at CERN for their support, and to the Royal Academy of Engineering for making this experience possible.