The new capture magnet, built from rare‑earth barium copper oxide (ReBCO) superconducting tape, reaches a peak field of 12.7 tesla—far above the 3.5‑tesla magnets used in current positron sources such as Japan’s SuperKEKB collider.

Operating at 15 kelvin, the ReBCO coil delivers a stronger field while simplifying cooling compared with conventional low‑temperature superconductors that must be kept near absolute zero.

Its purpose is to focus the spray of positrons created when an electron beam hits a tungsten target, a bottleneck identified for the 91‑km FCC‑ee that CERN plans to build as a successor to the 27‑km Large Hadron Collider.

“The FCC‑ee needs a much larger number of positrons than current technology can efficiently produce and capture,” said Paolo Craievich of PSI’s Center for Accelerator Science and Engineering. The magnet is designed to help achieve the FCC‑ee’s target intensity of 10^13 positrons per second.

Current facilities capture only a small fraction of the generated positrons; by raising the magnetic field to 12.7 tesla, the PSI design could dramatically improve capture efficiency, a point echoed by Iryna Chaikovska of the University of Paris‑Saclay.

The proof‑of‑concept system, dubbed P³, integrates the ReBCO solenoid with radio‑frequency cavities that accelerate the captured particles, and it has already demonstrated a functional positron beam.

A prototype of the solenoid was first tested at PSI’s SwissFEL x‑ray free‑electron laser facility in 2025, building on a 2024 design study led by Nicolas Vallis that highlighted the need for higher‑field superconductors.

The CERN Council gave priority to the FCC‑ee configuration in May 2026, and the collider’s scientific case depends on delivering high‑luminosity electron‑positron collisions to produce large numbers of Higgs bosons for precision studies.

With the Large Hadron Collider expected to cease operations in the 2040s, the PSI breakthrough addresses the urgent need for a next‑generation positron source capable of meeting the FCC‑ee’s demanding specifications.

The PSI team’s next steps include detailed benchmarking of the magnet’s performance, scaling the technology to full‑size requirements, and integrating it into a complete FCC‑ee positron‑source design.