Tucked away in an unassuming bunker at the CERN site that serves as an access point to the ALICE experiment, a small team of scientists and engineers are working to develop and test components of pre-injector accelerator systems so that they can be adapted for societal applications – including for medical and cultural heritage uses. 

The team, composed of members from CERN, the Spanish research institute CIEMAT, and the UNSA University of Sarajevo in Bosnia and Herzegovina, has set up a test stand at CERN’s Point 2 site in building 2250. 

There, supported by CERN’s Beams Department and Knowledge Transfer group, and partially financed by the “Three Physicist” Foundation, work is being carried out on three sections of a pre-injector accelerator system, all with the purpose of using these developments in compact particle accelerators for societal applications. 

The work has its roots in advancements that have been made over many years in designs of radiofrequency quadrupoles (RFQs), a key component in pre-injector systems. 

Expertise gained in designing the RFQ that is used in the Linear Accelerator 4 (Linac4), which today is the source of proton beams for CERN’s Large Hadron Collider, fed into the development of a high-frequency RFQ for proton therapy and other developments in compact, low-energy proton RFQs for societal applications. 

These compact RFQs have already been used in projects such as the mini ELISA accelerator set up at CERN’s education and outreach centre, the Science Gateway, and as part of the MACHINA project that aims to use[YF1]  an accelerator for cultural heritage applications. 

Now the team working in CERN’s building 2250 have taken a similar compact RFQ and are examining the proof-of-concept idea that it can be used as a pre-injector in a linac-based carbon-ion facility for cancer therapy and other medical applications. They are also carrying out separate but related work on extraction systems for a low-intensity proton source and an electron cyclotron resonance (ECR) ion source.

Technical developments

The first technical activity being undertaken at the bunker involves the installation of an RFQ accelerator – a 2.5-meter machine resonating at 750 MHz capable of accelerating helium ions (⁴He²⁺) and heavier ions (¹²C⁶), to 2.5 MeV/u. 

With planned tests of protons and helium acceleration, this system is intended to serve as a pre-injector for linacs capable of producing beams for cancer therapy centres or providing irradiation on targets for isotope production, including promising isotopes like Astatine-211.

The second activity centres on the commissioning of a commercially produced electron cyclotron resonance (ECR) ion source.

The aim of this project is to determine if the ECR source can be coupled with the RFQ and a low energy beam transport line (LEBT) to be used in areas of applied science such as material surface and depth analysis, as well as in low-energy physics. 

The source is designed to deliver a 100 μA helium beam or a 1 mA proton beam, with an extraction voltage of 30 kV. 

Beam diagnostics, including current measurement and emittance evaluation, are being carried out using a dedicated LEBT line equipped with advanced instrumentation. 

The source is being prepared for injecting beam into the RFQ, providing further acceleration to the helium and proton beams. 

The ion source is also set to continue as part of a test stand that will use particles with a ½ q/m ratio to teach students and others more about the technology and give them hands-on experience of using it. 

Lastly, the team is testing two extraction systems for a low-intensity proton source (100 mA, 15 keV), suitable for societal applications such as cultural heritage diagnostics. 

One system is optimised for compact RFQ injection, while the second provides more flexible beam manipulation through gridded lenses. The proton source will continue to be used as a studying point for societal applications related to artwork diagnostics, as well as tests for the ELENA (Antimatter Factory) ring at CERN.

Taken together, these three activities aim to develop key competences and teachings in linacs for societal applications.