Researchers at the Paul Scherrer Institute (PSI) in Switzerland have successfully produced the first positrons using a prototype source designed for CERN’s proposed Future Circular Collider (FCC).
The test system, installed at the SwissFEL X-ray free-electron laser facility, combines high-temperature superconducting magnets with new beam-control technologies to generate and capture positrons at high efficiency.
The milestone is significant because producing sufficient positrons and forming them into a usable beam is one of the major technical challenges facing the proposed collider.
PSI researchers have spent around five years developing the new source, which is intended to address limitations in existing positron-production technology.
Initial results indicate that the system could capture enough positrons to meet the demanding requirements of the FCC.
The successful first production demonstrates that the prototype’s key components can operate together and provides a foundation for further work to increase beam intensity and optimise performance.
The positron challenge facing the Future Circular Collider
The Future Circular Collider is being studied by CERN as a potential successor to the Large Hadron Collider (LHC).
The proposed facility would extend for around 91 kilometres beneath the French-Swiss border region, at an average depth of approximately 200 metres.
One stage of the FCC programme would use collisions between electrons and their antimatter counterparts, positrons. These collisions could provide researchers with a new way to investigate fundamental questions in particle physics that cannot be fully explored using existing machines.
However, an electron-positron collider requires a reliable supply of high-quality positrons. Existing sources are not capable of producing and efficiently collecting particles at the scale envisaged for the FCC, making the injector system a critical area of research.
New approach to positron production
The PSI prototype uses electrons accelerated by SwissFEL. When the electrons strike a tungsten target, they produce a shower of positrons travelling in different directions.
The source must then collect as many of these particles as possible and compress them into a tightly controlled beam. This is where the new technology developed at PSI is particularly important.
At its centre is a compact capture solenoid based on high-temperature superconducting technology. The magnet surrounds the production target and generates a very strong magnetic field, helping to collect the positrons before they are lost.
The system is designed to reach around 15 tesla. That is substantially higher than the 3.5-tesla capture magnet used by the SuperKEKB positron source in Japan, which is among the most advanced systems currently operating.
Other components then guide, separate and measure the particles. Radiofrequency systems accelerate and bunch the positrons, while newly developed diagnostic equipment records their number, timing and energy.
Together, these systems allow researchers to determine how effectively the source is producing a usable beam.
High-temperature superconductors could have wider uses
The magnet technology is one of the most notable elements of the project.
High-temperature superconducting materials can maintain strong magnetic fields at higher operating temperatures than conventional low-temperature superconductors, potentially reducing the energy required for cryogenic cooling.
The technology could therefore have applications beyond the Future Circular Collider and other particle accelerators.
PSI researchers are also investigating its potential for medical systems such as proton therapy gantry magnets, as well as applications in fusion research.
The work also builds on PSI’s experience with SwissFEL and forms part of broader collaboration with CERN on the FCC injector. This injector would produce, accelerate and prepare the electron and positron beams before they enter the collider.
Scaling up the positron beam
With the first positrons now produced, the next phase will focus on increasing beam intensity and refining the source so it can meet the FCC’s specifications.
The prototype is an early but important test of whether the proposed positron-production approach can be scaled to the requirements of a future large electron-positron collider.
Its performance will help inform the continued development of the FCC injector and the technologies needed to support a machine significantly larger than today’s LHC.
The project also highlights how advances developed for particle physics can extend into other fields. If the high-temperature superconducting magnet technology can be scaled reliably, it could contribute to a broader generation of accelerator systems with higher magnetic fields and potentially lower cooling requirements.
