Researchers 3D print copper components for compact particle accelerators

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A finished copper quadrupole quarter segment with material-saving hollow structures and cooling channels enabled by the flexibility of additive manufacturing. (Image: Fraunhofer IWS)

Researchers have additively manufactured components for a new generation of compact particle accelerators from pure copper.

The accelerators are being developed to improve cancer therapy, drug detection and material analysis.

Their compact size makes them more affordable and practical for deployment at locations such as smaller hospitals, airports and laboratories.

The work has been done as part of the Horizon 2020 project I.FAST, by Fraunhofer IWS together with the CERN, Riga Technology University and Politecnico di Milano.

The project is opening up new prospects for the commercial production and practical use of compact linear accelerators, which operate on the principle of high-frequency radio frequency quadrupoles (HF-RFQ). Unlike their usually huge underground brothers, called ring accelerators, these linear accelerators often take up little more space than a living room.

The quadrupoles, based on a new technology developed at CERN, are the key components and pacemakers for the accelerators. They comprise four alternately poled electrodes facing each other, arranged like petals around a central particle trajectory. Through the application of an alternating voltage, rapidly changing electric fields build up that send the particles between the wavy electrode tips and bring them closer and closer to the speed of light. 

Because the systems generate a lot of waste heat during long-term operation, the quadrupoles are made of pure copper – an exceptionally good conductor of electricity and heat. Until now, however, the production of quadrupoles has been very complex. They are milled into shape from semi-finished products and then assembled from a very large number of individual parts.

This is where the research partners saw great potential in 3D copper printing. They melt pure copper powder with a green laser and from this molten metal form the quarter segment of a quadrupole. In the process, they save material wherever it is not needed for component strength, reducing copper consumption and providing lighter quadrupole segments that can be assembled within one day.

‘This approach will allow us to significantly reduce manufacturing times,’ said Samira Gruber, an expert in additive manufacturing of pure copper and copper alloys at Fraunhofer IWS. This could enable rapid prototyping to become a driver for the future development of accelerator technology.

The researchers are now looking at potential post-processing techniques to complete the additively manufactured quadrupoles. This is because the built parts have rough surface topologies, meaning they must be analysed and subsequently smoothed. For this, the researchers are considering plasma, electrochemical or laser polishing methods. 

The project agenda also includes tests to determine whether and how minor wear damage on accelerators can be subsequently repaired using additive manufacturing technologies without having to scrap entire components. ‘In addition, we also intend to study which other materials and components can be considered for additive manufacturing for accelerators,’ explained Gruber.

The compact linear accelerators being developed within the I.FAST project could be used, for example, for better and more automated drug and weapons checks at airports. In the field of medical applications, they can also be used for proton therapy against particularly insidious tumors in the abdomen or brain, as well as for medical isotope production. CERN is even exploring other applications, including material analysis with the purpose of examining art masterpieces.

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