The new magnet, built from rare‑earth barium copper oxide (ReBCO) superconducting tape, operates at 15 kelvin and focuses the shower of positrons generated when an electron beam strikes a tungsten target, dramatically improving capture efficiency compared with the 3.5‑tesla magnets used at today’s operational sources such as Japan’s SuperKEKB collider.
CERN’s FCC‑ee, the electron‑positron version of the proposed Future Circular Collider, will need to deliver about 10¹³ positrons per second to achieve the high‑luminosity collisions required for precision Higgs‑boson studies. Existing capture technology cannot meet that demand, making the PSI breakthrough a critical step toward the collider’s feasibility.
“The FCC‑ee needs a much larger number of positrons than current technology can efficiently produce and capture,” said Paolo Craievich, head of PSI’s Center for Accelerator Science and Engineering. “Our 12.7‑tesla solenoid shows that a high‑field, high‑temperature superconductor can deliver the needed performance.”
The PSI team’s P³ system not only demonstrated the magnet’s field strength but also generated a functional positron beam, confirming that the approach can be integrated with downstream radio‑frequency cavities that bunch and accelerate the particles for injection into a circular accelerator.
Iryna Chaikovska of the University of Paris‑Saclay echoed the sentiment, noting that “the real challenge for a positron source is not only to produce enough positrons but also to capture enough of them,” and that the intensified magnetic field directly addresses that capture challenge.
The magnet design builds on a prototype tested at PSI’s SwissFEL x‑ray free‑electron laser facility in 2025 and on a 2024 design study led by Nicolas Vallis, which highlighted the need for a stronger field than conventional low‑temperature superconductors can provide. ReBCO’s higher critical temperature—below 93 K—allows operation at the relatively warm 15 K, simplifying cryogenic requirements while sustaining the required current density.
With the Large Hadron Collider expected to retire in the 2040s, the CERN Council’s May 2026 decision to prioritize the FCC‑ee makes rapid progress on positron sources urgent. PSI plans to benchmark the magnet’s performance in detail and to scale the technology toward the full specifications demanded by the future collider.