Having assessed the impact of the power disruption in November, ESS teams are establishing a new timeline to produce first neutrons within a year.
At the end of 2025, a power outage affected a critical component of the ESS target station – the moderator – which affected progress towards the production of first neutrons by ESS’ one-of-a-kind target system. ESS teams and in-kind partners promptly swung into action to assess the damage to the moderator, determine the impact on progress towards neutron production and establish a new timeline for this important milestone.
In close consultation with Forschungszentrum Jülich (FZJ), the in-kind partner that designs and builds the moderator, the ESS management team has decided that the best option is to focus on assembling, testing and delivering the second moderator as efficiently as possible.
Kevin Jones, ESS Director for Machine and Operations, explains, “Designing a second moderator was always part of the plan for the ESS machine, as a replacement for the first moderator. With the setback of last year, 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”.
The moderator is one of the most innovative components of the target station; it slows down neutrons as they come off the target wheel, bringing them to the right energy for the instruments. Moderator 2 has a different geometry and is expected to provide stronger neutron flux to the instruments, thus increasing their discovery potential.
In parallel, ESS is systematically examining the direct causes of the incident, with a view to safeguarding the facility against future setbacks.
Work across the ESS facility continues at pace. The accelerator is advancing to the next phase of commissioning, after successfully achieving Beam on Dump last year. The additional time will be used to optimise important beam parameters ahead of the target system being ready to receive the proton beam (Beam on Target).
On the instrument side, three additional instruments are expected to be ready at Beam on Target, alongside those already foreseen. This will support the longer-term goal of the full complement of 15 instruments receiving neutrons when ESS enters operation.
Despite the setback that directly affected it, work will continue on the target system to test that all components are functioning in an integrated way, ready for installation of the new moderator and the next phase – receiving protons from the accelerator.
Andrew Kimber, ESS Project Director, concludes: "Across the facility, ESS is driven by the objective to minimise the impact of the moderator incident on our overall goal, which is to produce neutrons and welcome scientists to do experiments by the end of 2027. All options for accelerating the process are being explored, with a view to establishing a revised plan by March 2026”.