The neutron moderators for the European Spallation Source

The European Spallation Source will have 42 beam ports as a grid available for a variety of instruments, mostly neutron scattering experiments. Bi-spectral extraction for thermal and cold neutrons must be available to all the beam ports. The moderator design to deliver such neutron beams was driven by the low-dimensional moderator concept. The adopted design, consisting of one flat (3 cm high) moderator placed above the spallation target was considered valid for the initial instruments suite. ESS will however have a beam port system designed such that it will be possible to extract neutrons from moderators above and below the target. With all initial instruments pointing to the top moderator, this opens the possibility to have different types of moderators at the bottom, so that other neutron beams of different intensity, or spectral shape, with respect to the ones delivered by the top moderator, could be envisaged, adding additional scientific opportunities to the facility.