Target Wheel and Moderator have been installed

Moderator installation

We are pleased to announce the successful installation of the Target Wheel and shaft and the Moderator Reflector Plug into the Target Monolith. This is a major milestone on the ESS Road to Science.

View from above looking down a circular hole where a shiny metal wheel shaped component sits snugly

On Friday 24 November the target wheel was lowered into the monolith

The target wheel, which contains 7000 bricks of tungsten, will be the source of neutrons used by researchers at the ESS in the future.  It is a 2.6 m rotating wheel, suspended from a shaft that will rotate at approximately 23.3 revolutions per minute. As high energy protons from the accelerator strike the tungsten atoms, spallation occurs, generating the neutrons. The target wheel was an in-kind contribution from our partner ESS Bilbao.

The moderator is positioned so it sits above the part of the target wheel that is being struck by the beam of protons. Its job is to slow down the neutrons after spallation to an energy suitable for the researchers to use on their samples in the instruments. The moderator was installed in a replaceable plug, along with a beryllium-lined neutron reflector, and all the systems to keep the system cool. This so-called Moderator Reflector Plug is designed to be replaceable every few years as upgraded versions become available, and was delivered by our in-kind partners Forschungszentrum Jülich.

Both of these components were delivered to ESS during 2022 and have undergone intensive testing in the mean time in a separate Mock Up and Test Stand to ensure they meet all the appropriate quality and function requirements.

The next step is for the Survey, Alignment and Metrology Team to perform precise alignment of these key components.

More information on the whole target system can be found here:

We wish to thank all those involved, and especially to our in-kind partners ESS Bilbao in Spain and Jülich in Germany.

Forschungszentrum Jülich logo


Click on the image below to watch a 12 minute film of this key milestone from some of the many people involved.

In November 2023, ESS achieved a major milestone in installing the Target Wheel and Moderator Reflector Plug, key components for the neutron production at the facility. This movie shows the installation with commentary and explanations on how it works and why it is important, presented by ESS staff and In-Kind Partners. In-Kind Partner for the Target Wheel: ESS Bilbao, Spain. In-Kind Partner for the Moderator Reflector Plug: Forschungszentrum Jülich, Germany