Newly developed thermal conducting material holds promise for use in future accelerators and industry
The search for a scalable replacement for copper as a thermal conducting material in high thermal management applications has been an ongoing process for over a decade. Copper is still useful as a thermal conductor – it’s cheap, effective, can be produced in large quantities and can be shaped for use on large components. But in certain cases, such as CERN’s Large Hadron Collider (LHC) and other specific industrial settings, there is a need for a material that possesses low density and can manage not only extreme heat, but also extreme structural pressure.
That is why CERN has, through various EU-funded projects and with the help of industrial partners Brevetti Bizz and Nanoker, been working on finding a suitable replacement. The work has centred on carbide-carbon materials (CCMs), which combine the toughness of carbides with the versatility of carbon, making them ideal as thermal conductors in tough conditions.
One solution, molybdenum-graphite (MoGr), has already been successful to some extent. It was initially devised for application in CERN’s upgraded High Luminosity LHC, which is scheduled to begin operations in 2030, as part of the collimators – devices used to control and shape the beam of particles.
These devices must operate very close to the particle beam and therefore have to dissipate significant power densities. A suitable and light thermal conducting material did not exist on the commercial market.
The goal was set to find a material that had: high thermal conductivity (two times higher than the best “standard” conductor, i.e. copper), good electrical conductivity, low density, low coefficient of thermal expansion and good mechanical properties.
After significant research and development of MoGr, teams at CERN managed to prototype and then industrialise the material, allowing in 2020 the construction of 15 collimators equipped with ~300 MoGr absorber blocks. Twelve of these collimators are actively being used during the current Run 3 of the LHC, which started in 2022 and will end in 2026.
The excellent thermophysical properties of the MoGr make it very appealing for a range of industrial and technological applications well beyond high-energy physics and colliders.
Potential fields of application for the material include high-power electronics, aerospace, fusion and nuclear fields, where reduced thermal expansion and low density are required along with high thermal conductivity and thermal shock resistance.
However, the extensive use of MoGr in industry and research centres has so far been hindered by its high production cost and the limited size of the blocks that can be produced.
When comparing good thermal conductors, high purity copper has a cost per unit volume of around €0.15 per cm3, isotropic graphite, which is lighter but less conductive, costs about 10 times more, and MoGr, lighter still and more conductive, costs around 100 times more than copper.
What’s more, the maximum size of a CCM part that it has been possible to produce has been limited to 400 cm3. Finally, the production process of such a CCM is energy consuming, requiring high machine power to reach the required sintering temperature, which is above 2600 °C. For these reasons, currently the application of CCMs can only be limited to very high-end applications, where the material cost is secondary with respect to performance.