A team of researchers at CERN has developed innovative hollow-core optical fibers that can withstand extreme radiation, potentially transforming monitoring techniques in particle accelerators. These fibers, which are no thicker than a human hair, are currently being tested at the Super Proton Synchrotron, CERN’s second-largest accelerator, located in the North Area.
Traditional optical fibers guide light through solid glass, but hollow-core fibers employ a unique microstructure that uses resonance and antiresonance effects to channel light. By filling these fibers with a scintillating gas, which emits light when struck by particles, scientists have created a powerful radiation sensor. This technology not only improves the monitoring of beam profiles and positions but may also allow real-time measurement of the delivered beam dose.
The implications of this development extend beyond CERN’s operations. Current monitoring tools, like multi-wire proportional chambers and scintillator detectors, often fail in high-radiation environments. The reliability of these systems is critical for experimental physicists and beam physicists, particularly as the field moves towards new medical applications such as FLASH radiotherapy, which administers radiation at ultra-high dose rates for cancer treatment.
In collaboration with medical researchers, CERN’s team is exploring tools that can endure the extreme conditions posed by advanced accelerators. This work is crucial for developing safe monitoring systems for FLASH therapy, which requires innovative solutions to manage its demanding beam conditions.
Testing of this new fiber technology took place at CERN’s various facilities, including the CLEAR facility, throughout 2024 and 2025. The researchers exposed a fiber filled with an argon-nitrogen mixture to an electron beam and connected it to a silicon photomultiplier, a device capable of detecting single photons. Each exposure caused the gas within the fiber to emit light, which was then transmitted to the detector.
The initial results, presented at this year’s International Beam Instrumentation Conference, showed promising alignment with traditional measurement methods. According to Inaki Ortega Ruiz, who leads the beam instrumentation consolidation for the SPS North Experimental Area, “The fiber’s measurements of the beam profile closely matched those from a traditional YAG screen, a crystal that glows when struck by particles.” Remarkably, even after exposure to radiation doses that typically damage many instruments, the fiber demonstrated no loss of performance.
While these findings are encouraging, the research team plans to enhance the connection between the fiber and the detector, test sealed fibers pre-filled with gas, and assess the long-term radiation resilience of the fibers. The ongoing collaboration between accelerator experts and medical researchers holds the potential for significant advancements in both scientific and medical fields, underscoring the importance of innovative monitoring technologies in the future of particle physics and cancer treatment.
