Commissioning of the cryogenic hydrogen system in J-PARC: Preliminary operation by helium gas

A cryogenic hydrogen circulation system to cool the moderators for the spallation neutron source in J-PARC has been constructed. This system provides supercritical hydrogen at the temperature of 20 K and the pressure of 1.5 MPa to three moderators and absorbs nuclear heating produced in the moderators. The cryogenic hydrogen system commissioning was started. In January 2008, for the first time, we carried out a cryogenic test of the whole system, in which helium gas was used in stead of hydrogen. The cryogenic hydrogen system can be cooled down to 18 K within 30 hours, and be kept to be the rated condition for 36 hours without any problems. We confirmed the soundness of each component such as circulation pump and operation control system.