As a key part of the particle tracker support structures for the LHC’s Compact Muon Solenoid (CMS) detector, Exel’s pultruded profiles had to satisfy strict dimensional tolerances and sustain the highest level of performance in this challenging environment, where any downtime or failure would impact major scientific experiments.
The LHC is the world’s largest and most powerful particle accelerator. It consists of a 27 km ring of superconducting magnets with a number of accelerating structures to boost the energy of the particles along the way. Inside the accelerator, two high-energy proton beams travel at close to the speed of light, in opposite directions, before they are made to collide at four locations around its ring. The CMS detector sits at one of the four collision points and records the paths taken by particles using a silicon tracker consisting of around 75 million individual electronic sensor channels arranged in 12 concentric layers. The tracker needs to record particle paths with very high precision yet be lightweight so as to disturb the particles as little as possible.
The Exel components are part of the 688 high-precision structures supporting the silicon tracker modules. These are made up of two 1.2 m long carbon fibre epoxy composite U-profiles of 0.7 mm wall thickness and L-shaped cross-bars to form a frame structure on which the particle detecting modules sit. In addition to delivering the lightweight and radiation transparency required for this application, it was critical that the Exel profiles met extremely tight tolerances in terms of dimensions and straightness and maintained all mechanical properties at the low temperatures encountered in the CMS. In order to provide the high levels of stiffness and thermal stability required the company designed the profiles using high modulus unidirectional (UD) carbon fibre. A thin glass fibre surface tissue was also employed to facilitate processing. All of the components and fixtures were then assembled and bonded on jigs at the Helsinki Institute of Physics to create structures with a dimensional tolerance of ± 0.05 mm.
Exel’s capabilities in the production of high performance thin-walled pultruded profiles and the company’s experience in designing with high modulus carbon fibres are said to be key success factors in this project. Exel has also collaborated with CERN before, supplying around 200 km of electrically insulating glass fibre profiles to frame the superconductive busbars of the LHC.
Exel delivered the tracker support profiles to CERN from 2001 to 2005, with the final operational use starting in 2008. The CMS detector has been performing excellently, culminating in 2012 with the discovery of a new elementary particle, the Higgs boson.
“We are very satisfied with the high level of technology and development support offered by Exel Composites,” comments Antti Onnela, CMS Tracker Project Engineer at CERN. “We had quite challenging requirements for these composite structures and earlier laminated versions did not meet them. Exel developed the needed thin-walled U-profiles that turned out to be technically superior, but also more economical thanks to the production process that minimised the wastage of expensive carbon fibres. After nine years in service in the CMS the Exel parts continue performing as flawlessly as in the beginning.”
Companies: Exel Composites