Through the collaboration of the Japan Atomic Energy Agency and High Energy Accelerator Research Organization, the Japan Proton Accelerator Research Complex (J-PARC) has been constructed. The prime purpose is to use the various secondary particle beams such as neutrons, mesons and neutrinos produced in proton-nucleus reactions. One of the facilities that has already been completed is a materials and life-science experimental facility (MLF) where materials and biological structures are analyzed by neutron beam-scattering experiments. In the MLF, a spallation neutron source that provides a high-intensity pulse neutron with low-order meV energy for scattering experiments has been completed, and has successfully produced the desired neutrons. Neutrons produced by spallation reaction have high-order MeV energy, and the high-energy neutron is then transformed to meV-order energy by passing it through a supercritical hydrogen moderator. Therefore, a cryogenic hydrogen system is equipped in the spallation neutron source system. This paper describes the first operation results of the cryogenic hydrogen system.
