A new generation of particle accelerators is set to take cancer therapy, drug detection and material analysis to a higher level.

These linear accelerators are so compact that they are affordable even for smaller hospitals, airports and laboratories. To promote this development, the Fraunhofer Institute for Material and Beam Technology IWS, together with the European Organization for Nuclear Research (CERN) in Switzerland, the Latvian Riga Technology University (RTU) and the Politecnico di Milano (PoliMi), is focusing on laser-based 3D printers: as part of the "I.FAST" project, which aims to promote innovation in accelerators and is co-funded by the European Commission under the Horizon 2020 program, important quadrupole components for linear accelerators have now been additively manufactured from pure copper powder for the first time in the world.

This opens up new prospects for commercial production and the practical use of such systems, which are based on the principle of "High Frequency Radio Frequency Quadrupoles" (HF-RFQ). This could, for example, enable better and more automated drug and weapons checks at airports. The researchers see great potential in 3D copper printing: "This will allow us to significantly reduce production times," predicts Samira Gruber, who is an expert in the additive manufacturing of copper and copper alloys at the Fraunhofer IWS. "This makes it possible to build prototypes quickly, for example. This can significantly advance the further development of accelerator technology." Additive manufacturing can also save material and thus reduce the consumption of copper resources compared to conventional processes.

What are quadrupole accelerators?

These arguments carry considerable weight if these compact accelerators are to become more widely accepted. This is because high-frequency quadrupoles, which are based on a new technology developed at CERN, are the key components and clock generators for this new generation of systems. In the quadrupoles, four alternately polarized electrodes face each other and are arranged like petals around a central particle trajectory.

When the user applies an alternating voltage, rapidly changing electric fields are generated. These send the particles between the wavy electrode tips on a kind of wave ride that brings them closer and closer to the speed of light with each quadrupole they pass. Unlike their usually huge underground brothers, the ring accelerators, these linear accelerators often take up little more space than a living room.

Green laser makes the previously impossible possible in component optimization

Because the systems generate a lot of waste heat during long-term operation, the clocking quadrupoles are made of pure copper. This metal conducts electricity and heat particularly well. 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 large number of individual parts. This is why researchers at the Fraunhofer IWS, RTU and PoliMi have now developed an alternative. They use a green laser to melt pure copper powder.

They then form the quarter segment of a quadrupole from this molten metal. In doing so, they save material wherever it is not needed for component strength. In classic metal processing methods, on the other hand, this component optimization is very time-consuming and in some places not even feasible. The new production method therefore reduces copper consumption and ensures lighter quadrupole segments that can be assembled within a day.

An increase in the installation space of laser melting systems with green lasers will soon make it possible to produce entire quadrupole segments using 3D printing. However, the next project phases are already possible with the quarter segments produced now: for example, experience has shown that components from additive manufacturing have rough surface topologies. This means that their surface is often rough. The prototype therefore needs to analyze whether and how the 3D printed quadrupoles need to be subsequently smoothed - for example by means of plasma or electrochemical polishing.

The project agenda also includes tests to determine whether and how minor wear damage to accelerators can be subsequently repaired using additive manufacturing technologies without having to scrap entire components. "We also want to investigate which other materials and components are suitable for additive manufacturing for accelerators," says Samira Gruber.

Conceivable use for proton therapy and automatic drug detection

The linear accelerators are not only of interest to particle physicists. In the field of medical technology, they can be used for proton therapy against particularly insidious tumors in the abdomen or brain as well as for the production of medical isotopes. Many other applications for quadrupole accelerators are being researched at CERN - including material analysis - with the aim of examining masterpieces of art.

Accelerators offer significant market opportunities. In their 2012 analysis "Industrial Accelerators and Their Applications", Californian industry experts Robert Hamm and Marianne E. Hamm estimate that there are currently around 30,000 accelerators in use worldwide, which companies and institutes around the world use to produce and analyze industrial goods worth 500 billion US dollars per year.