Helmut Schober, Director General of the European Spallation Source (ESS), shares an update on the progress made so far in the construction of Sweden’s next-generation neutron science facility.
The European Spallation Source is a next-generation neutron science facility under construction in Lund, Sweden, with its Data Management and Scientific Computing Centre located in Copenhagen, Denmark. Once completed and fully operational, ESS will be a world-leading accelerator-based neutron source for studying the structure and behaviour of materials at the atomic level.
ESS, which has been in construction since 2014, is one of the largest science and technology infrastructure projects being built today. The facility design and construction include the most powerful linear proton accelerator ever built, a five-tonne, helium-cooled tungsten target wheel, 15 state-of-the-art neutron instruments, a suite of laboratories, and a supercomputing data management and software development centre.
To learn more about the progress made so far and the great potential for science that will come from the facility, The Innovation Platform spoke with Helmut Schober, Director General of ESS.
Can you elaborate more on what ESS will deliver and what makes it different?
ESS has been designed to generate the world’s most powerful neutron beams for research in materials science, chemistry, biology, energy, and other fields. Unlike nuclear reactors, ESS uses high-energy protons striking a tungsten target to produce neutrons – a process called ‘spallation’.
The exceptional brightness of the neutron beams and its long-pulse source design set it apart from other spallation sources, enabling experiments with greater sensitivity, resolution, and speed. ESS will have the potential to transform areas such as energy materials, pharmaceuticals, catalysis, and nanotechnology, facilitating breakthroughs that are not possible with existing neutron sources.
What stage of construction is the facility at currently?
In 2025, the accelerator, target station, integrated control systems, and several initial neutron scattering instruments advanced significantly towards commissioning. The accelerator delivered first full-energy low-power test beam to a tuning beam dump to demonstrate full integrated operation of this important part of the facility. The current focus is on continuing system verification, validation, and commissioning and establishing safety and operational readiness.
In the accelerator, a second Beam on Dump commissioning period will take place this spring at higher power than last year’s Beam on Dump.
Progress on the ESS target – unique in the field of neutron science and spallation – suffered a setback at the end of 2025 (more about the incident below). However, integration tests are continuing, and the teams have identified mitigation factors for the setback that will allow for what we call the ‘neutron factory test’ by the end of the year.
The first set of six instruments is being prepared to receive neutrons, and the installation of the next set of instruments is advancing, positioning them to start the user programme in 2028, when scientists from all around the world will come to ESS to carry out experiments.
What were the main technical issues you faced, and how were these overcome?
Major technical challenges have included: precision installation and alignment of the 600-metre superconducting accelerator; ensuring high reliability and safety of the cryogenic systems; realising the complex neutron target (with its rotating tungsten wheel and extensive shielding); and integrating digital control systems across diverse technologies and partner contributions.
These challenges were overcome through rigorous prototyping, international collaboration, adaptive project management, intensive testing before and during commissioning, and continuous knowledge sharing among partners.
Our most recent challenge happened at the end of 2025, when a power dip affected a critical component of the target station – the moderator – and stalled progress towards the production of the first neutrons. The moderator is one of the most innovative components of the target station, slowing down neutrons as they leave the target wheel, bringing them to the appropriate energy for the instruments.
ESS teams and in-kind partners promptly took 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. A replacement moderator, which was already in production at the time, will be installed and tested in the last quarter of 2026.
What were the key achievements in 2025?
In 2025, ESS marked several important achievements- the most significant being reaching Beam on Dump. For the first time, protons were accelerated to the required energy and delivered all the way from the ion source to the tuning beam dump – 542.5 metres down the 600-metre-long accelerator tunnel. This achievement demonstrates that the ESS accelerator and associated control systems are functioning as an integrated system, from source to dump.
Other achievements included expanded installation and commissioning of the first suite of neutron instruments; receipt and installation of key hardware components from partner institutions; and further development of data management and preparations for the user programme.
In parallel, ESS continued its transition towards steady-state operations, further developing the organisational structures and operational processes required to ensure reliable and efficient facility operation as of 2028.
The progress made in 2025 reflects the collective efforts of hundreds of people across ESS teams, disciplines, and partner institutions, all working together towards a single goal: generating neutrons for science.
What is 2026 set to look like?
Work continues apace across the ESS facility. Despite the moderator setback, work will proceed on the target system to test that all components are functioning together, so that the system is ready for installation of the new moderator and the next phase – receiving protons from the accelerator. The accelerator itself is advancing to the next stage of commissioning, having successfully achieved Beam on Dump last year, and is currently preparing for the second Beam on Dump commissioning period.
On the instrument side, three additional instruments are expected to be ready at Beam on Target, in addition to the three already planned. This will move ESS towards the long-term goal of a full suite of 14 (and later 15) instruments receiving neutrons when the facility enters operation.
How important has European contribution and collaboration been for ESS?
European collaboration is fundamental to ESS’s success. Over 100 institutions from 13 European countries have contributed expertise, design, hardware, and funding. This collaborative model has enabled access to leading scientific, technical, and engineering talent, accelerated development, and ensured broad scientific relevance. The partnership model also supports distributed responsibility for instrument construction, data management, and long-term governance.
Please note, this article will also appear in the 25th edition of our quarterly publication.