ESS postpones first neutron production by one year due to technical issue
The European Spallation Source (ESS) has announced a revised timeline, pushing the production of its first neutrons back by approximately one year due to a critical technical failure in its target station. The new target for first neutrons is now set for early 2027.
The European Spallation Source (ESS) facility will delay its first neutron production by approximately one year following a significant technical issue. A power disruption in late 2025 affected a critical component in the target station, known as a moderator, impacting progress towards generating neutrons.
ESS teams and partners have been working to assess the damage and its effects on the project timeline. Following consultation with Forschungszentrum Jülich (FZJ), the in-kind partner responsible for the moderator, ESS has decided to prioritize the assembly and testing of the second moderator. "We will now make every effort to ensure that moderator 2 will be ready to be installed and tested in the last quarter of 2026," stated Kevin Jones, ESS Director for Machine and Operations.
The moderator is essential for slowing down neutrons to the precise energy required for scientific instruments. ESS is also investigating the root cause of the incident to prevent future setbacks. Meanwhile, other parts of the facility are advancing, with accelerator commissioning progressing and additional time allocated for optimizing beam parameters.
While the overall goal remains to welcome scientists for experiments by the end of 2027, the moderator incident necessitates a revised plan. Project Director Andrew Kimber indicated that all options are being explored to minimize further delays, with a definitive updated plan to be established by March 2026.