A team at CERN has made significant progress in monitoring particle beams using innovative hollow-core optical fibers. These slender glass fibers, no thicker than a human hair, are being tested to enhance the measurement of beam profiles and positions in the Super Proton Synchrotron (SPS), CERN’s second-largest accelerator. This advancement could lead to more accurate and reliable monitoring in high-radiation environments.
Innovative Fiber Technology for High-Radiation Environments
Unlike traditional optical fibers that guide light through solid glass, hollow-core fibers utilize a unique microstructure design that allows light to travel through resonance and antiresonance effects within an electromagnetic field. By filling these fibers with a scintillating gas—capable of emitting tiny flashes of light when impacted by particles—researchers can create effective radiation sensors. These sensors enable scientists to adjust beam profiles and positions while potentially measuring the delivered beam dose in real time.
The ability to function in extreme radiation conditions sets these hollow-core fibers apart from conventional multi-wire proportional chambers and scintillator detectors. This characteristic is particularly valuable for CERN’s future projects and experiments, as reliable measurements of particle beams are vital for both experimental and beam physicists. The operation of CERN’s accelerators depends heavily on data from thousands of beam sensors distributed throughout the machines, but their accuracy can diminish under high-energy or high-intensity circumstances.
Applications in Medical Technology
Research into these advanced sensors is not limited to particle physics; it has promising implications for medical applications as well. The development of accelerators for medical treatments, such as FLASH radiotherapy, necessitates new monitoring tools that can withstand extreme beam conditions. FLASH radiotherapy, which delivers radiation at ultra-high dose rates, shows considerable potential for cancer treatment. However, it requires innovative technologies to ensure safe and effective delivery.
CERN’s team, focused on beam diagnostics, is collaborating with medical researchers to explore these new tools. By merging accelerator expertise with medical technology, the hollow-core optical fibers tested in CERN’s North Area could someday support the safe administration of FLASH therapy to patients.
The initial testing of this concept took place at various CERN facilities, including CLEAR, during 2024 and 2025. Researchers exposed fibers filled with an argon-nitrogen mixture to an electron beam while connecting them to a silicon photomultiplier—a sensor capable of detecting single photons. Each time the electron beam passed through, the gas illuminated, and the fiber transmitted that signal to the detector.
The results, presented at the International Beam Instrumentation Conference, showed promising outcomes. According to Inaki Ortega Ruiz, who leads the beam instrumentation consolidation of 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 could damage many instruments, the fiber displayed no signs of performance degradation.
While these initial findings are encouraging, further research is needed. Plans include enhancing the connection between the fiber and the detector, testing sealed fibers pre-filled with gas, and studying the long-term radiation hardness of the fibers. The potential of this technology could mark a significant step forward in both particle physics and medical applications.
