The Cryogenic Moderator System Cryostat Design for the European Spallation Source

The European Spallation Source in Lund, Sweden, is going to be a neutron scattering research center that aims to provide around 30 times brighter neutron beams than any other existing facility. As one subsystem of the Target Station, the Moderator & Reflector System slows down high energy neutrons from the spallation process. To gain maximum neutron flux intensities along with high system availability for condensed and soft matter research, an optimized liquid hydrogen Cryogenic Moderator System (CMS) has been developed. Hydrogen with a pressure below critical, an inlet temperature of around 17 K, and a parahydrogen fraction of at least 0.995 will be utilized to interact with neutrons in a unique Moderator vessel arrangement. Two turbo pumps are arranged in series and circulate the cryogen. The pressure stabilization is achieved by an active pressure control buffer in a bypass stream between high pressure and low pressure side. Hydrogen conversion from ortho- to parahydrogen will be controlled and monitored using a catalyst bed in a second bypass line between the high and the low pressure branch of the circuit. A helium refrigerator, the Target Moderator Cryoplant (TMCP), continuously recools the hydrogen mass flow.