Superfluid-helium Ultracold Neutron Sources: Concepts for the European Spallation Source?

Production of ultracold neutrons by conversion of cold neutrons in superfluid helium can be implemented in several ways, with the converter located either “in-pile” close to the core of a nuclear reactor or closely coupled to a neutron spallation source, or at the end of a neutron guide. This paper shall contribute to a discussion about source concepts for the ESS.