Development of the cryogenic hydrogen system for a spallation neutron source in J-PARC

Tatsumoto, Hideki; Aso, Tomokazu ; Otsu, Kiichi; Uehara, Toshiaki; Sakurayama, Hisashi; Kawakami, Yoshihiko; Kato, Takashi; Futakawa, Masatoshi  

In JSNS, supercritical hydrogen at around 20 K and 1.5 MPa was selected as a moderator material. Three kinds of hydrogen moderators are installed to provide pulsed neutron beam with higher neutronic performance. A cryogenic hydrogen system, in which a hydrogen circulation system is cooled by a helium refrigerator system with the refrigerator capacity of 6.45 kW at 15.6 K, provides the supercritical hydrogen to the moderators and absorbs nuclear heating in the moderators. Through the off-beam commissioning, we have confirmed that the cryogenic hydrogen system can be cooled down to 18 K within 19 hours. The supercritical hydrogen with the mass flow rate of 190 g/s can be circulated at the rated condition. It is verified that the cryogenic hydrogen system is satisfied with the performance requirements. In May 2008, we have succeeded in providing the first cold neutron beam cooled by the cryogenic hydrogen system.