Liquid hydrogen moderator for the European Spallation Source, ESS

The European Spallation Source (ESS) project is under design in Lund (SE) to provide 22 neutron beam-lines dedicated to materials science researches. The neutron scattering technique is driven by a 5-MW proton beam accelerator hitting a Tungsten target. The resulting neutrons are moderated to the appropriate energy (meV range) by means of moderator systems using liquid hydrogen. The design of the target station requests a dedicated and reliable cryogenic circuit. From a safety point of view it is of importance to prevent possible chemical reactions between hydrogen and the environment. The main hazardous conditions to consider are explosion, radiation, erosion/corrosion and overpressure. In this paper, we introduce the cryogenic engineering processes proposed to safely operate the ESS target station. (author)