Target Moderators

The ESS Target concept will secure the best scientific performance combined with safety and minimum environmental impact. Since the neutrons used for the experiments are produced in the target station, the design of the target station is of vital importance to future scientific opportunities and performance. ESS will use a novel design for spallation targets, consisting of a solid, rotating tungsten wheel. Since ESS will be the most powerful neutron source ever constructed, gradually ramping up to 5 MW, the design of the target required a significant amount of design work. The target station selected technologies will convert protons to neutrons, remove heat deposited by 5 MW proton beam and protect public, workers, and the environment from radioactive hazard.

Adjacent to the target wheel, there are two moderators: an “Upper Moderator” above the wheel and a “Bottom Moderator” below. They can both be rotated on their shaft and removed from the monolith for service or replacement. The new moderator is more generic and will be able to support all 15 planned instruments at ESS. As the top moderator is optimised for brightness, the bottom moderator could be optimised around intensity.


  • A comprehensive exchange of resources and knowledge between ESS and Spallation Neutron Source (SNS) in the United States is in place so the moderator development at ESS can be evaluated and discussed with a live facility.
  • As part of the exchange, the moderator plug will also be evaluated and tested as possible, as is the case for the new titanium oxide coated cupper optics.
  • There is a strong consortium of the EU-funded HighNESS project, with the leading neutron facilities and universities on-board.
  • There is a unique technology opportunity at ESS to focus on brightness with the upper moderator and on flux with the bottom moderator.


  • ESS will further support the technology revolution of high brightness neutron moderators for the future solutions.
  • The HighNESS project will address a lot of material issues and challenges and by that support the selection of the best concepts for high flux moderation and also towards the development of a Very Cold Neutron (VCN) moderator.
  • The relationship between facilities is strong, but with the ESS initiatives the new technology developments can be coordinated and qualified.
  • As ESS is moving closer to operation there is encouragement to open up for further external collaboration so more can use the ESS components and by that providing minimisation of technology risk for ESS.
  • The unique ESS moderator solutions should be promoted and communicated worldwide.