Cold moderators for the High Brilliance Neutron Source

Abstract

Long-wavelength neutrons for the investigation of nano-scale materials are an indispensable tool in neutronresearch. With the decommissioning of several European nuclear research reactors in recent times compactaccelerator-driven neutron sources (CANS) are of interest in providing scientists with the necessary capacityof neutrons to conduct experiments.At the High Brilliance Neutron Source (HBS) project, multiple cold moderators will be positioned inside thesame Target-Moderator-Reflector unit (TMR), each providing its own instrument with cold or even verycold neutrons. All of these moderators can therefore be optimized in terms of material, operating temperatureand geometry, depending on the requirements of the instrument.In a first approach, two cryogenic moderator systems for a prototype TMR have been designed and arecurrently being manufactured at Forschungszentrum Jülich. While one is a closed-cycle liquid parahydrogensystem, the other one allows the batch-wise production of solid moderators, e. g. frozen methane. Bothmoderators are positioned as close to the target as possible by using so-called moderator plugs (MPs). Theseconsist of a vacuum-insulated cryostat with a detachable fluid transfer and moderator section, a neutronguide and surrounding radiation shielding.The planned operation of these cryogenic moderator prototypes from summer 2022 will enable theexperimental investigation of different cold moderator geometries, as well as various options for thesurrounding thermal moderator and reflector. The obtained results can then be used to validate andcomplement nuclear simulations, proof efficient operation and will allow more reliable future designs ofsuch cold neutron sources