Inside the European Spallation Source ESS: How Neutrons Unlock Next Generation Materials

In this video, the B1M team visits the European Spallation Source ESS near Lund to explain how neutrons are produced and used to study materials at the atomic level. The tour covers the proton accelerator, the spallation target wheel, shielding structures, and the instrument halls where neutron beams are captured for scientific experiments with potential applications in energy, medicine, and computing.

Introduction to ESS

Deep in southern Sweden, the ESS represents a multi nationality effort to build one of the largest science infrastructures in history. The facility uses a proton accelerator to generate neutrons that act as a tiny, highly precise probe into the atomic structure of materials. The goal is to advance energy technologies, health care, and the future of quantum computing by providing researchers with unprecedented neutron beams.

From Protons to Neutrons

The process begins with a proton beam travelling through a vacuum tunnel toward a heavy metal target. When protons strike the tungsten wheel in the target, neutrons are ejected in a spallation process. This is not a reactor or a chain reaction, but a controlled collision that liberates neutrons for use in experiments. The proton beam at ESS is designed to be highly powerful, with a 5 megawatt capability, delivering beams far stronger than many prior facilities.

Once produced, neutrons are slowed to usable speeds by a moderator reflector system using hydrogen and water. At the wheel, the protons hit 96 percent of the speed of light and the neutrons exit for transport along beamlines to instruments around the site.

The Accelerators, Target Wheel and Shielding

The ESS accelerator tunnel houses a complex array of magnets known as LAC worm units that keep the proton beam tightly focused inside the beam pipe. The target wheel itself is a disk weighing about five tonnes and made of tungsten blocks, surrounded by heavy shielding to protect personnel from radiation. The wheel spins at a precise 23.3 revolutions per minute and has 36 radial segments. Each segment must be struck by a proton beam during every rotation to maintain a steady neutron supply. Helium cooling at the rate of about 2.8 kilograms per second keeps the wheel at safe temperatures.

The Monolith and Active Cell

Surrounding the target is the Monolith, an eight metre high, 6000 tonne shielding chamber that houses the wheel and its protective environment. Above the active region lies a 500 tonne lid that weighs heavily under radiation protection demands. Beneath the floor lies the active cell, a heavily reinforced area where radioactive components are moved, processed, and stored by robotic arms controlled from a safe room. The construction used extra strong concrete with iron ore to increase density and shielding effectiveness.

Instrumentation and Data

ESS hosts around 15 scientific instruments at the end of multiple beamlines. These instruments, nicknamed Odin, Magic, Dream, Beer and others, capture data from neutron scattering events when samples are probed. Data from all instruments is processed at a separate data management and computing center near Copenhagen before researchers access it. When fully operational, ESS will enable about 3000 scientists each year to perform a wide range of experiments, from studying new superconductors to testing materials under extreme conditions for future technologies.

Collaboration, Funding, and Economic Impact

The ESS is a collaboration of more than a dozen European nations. The project was conceived to share costs and expertise, with an overall budget around €3 billion. Host nations Sweden and Denmark provide roughly half the funding, while the remainder comes as in kind contributions from other member states. In kind contributions include equipment, personnel, and know how delivered by partner institutions across Europe, enabling the facility to be built in a cost efficient way.

Timeline and Milestones

Construction of the accelerator began in 2017 and has progressed in stages. A major milestone came in May 2025 when beam on dump tests demonstrated the accelerator could operate. Officials project that neutrons will be produced on target by March 10, 2026, with a concentrated period of commissioning to follow as instruments are brought online. By 2027 ESS plans to have first neutrons ready for researchers and initiate a broad program of instrument development and experiments.

Environmental Design and Community Integration

From ground level ESS is designed to minimise visual disruption to the surrounding farmland and meadows. The distinctive Sombrero roof on the Target building is a striking feature but the site blends with its rural setting. Excess heat from ESS will be used to heat parts of the city of Lund, highlighting a thoughtful approach to energy efficiency and community integration.

Broader Impact and Future Prospects

Neutron sources like ESS present a powerful tool for materials science, energy research, and medical technology. The ability to image and analyze materials non destructively at the atomic scale can accelerate the development of better batteries, superconductors for MRI machines, and quantum computing components. The project also represents a model of international collaboration that spreads costs and expertise while pushing technology forward through shared capabilities.