title: Spallation ultracold neutron source of superfluid helium below 1 K.
abstract: For the production of high-density ultracold neutrons (UCNs), we placed 0.8 K superfluid helium in a cold neutron moderator. We resolved previous heat-load problems in the spallation neutron source that were particularly serious below 1 K. With a proton-beam power of 400 MeV×1 μA, a UCN production rate of 4 UCN cm(-3) s(-1) at the maximum UCN energy of E(c)=210 neV and a storage lifetime of 81 s were obtained. A cryogenic test showed that the production rate can be increased by a factor of 10 with the same storage lifetime by increasing the proton-beam power as well as (3)He pumping speed.
authors.affiliation: High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Masuda
authors.forename: Kichiji
authors.initials: K
authors.lastname: Hatanaka
authors.forename: Sun-Chan
authors.initials: SC
authors.lastname: Jeong
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Kawasaki
authors.forename: Ryohei
authors.initials: R
authors.lastname: Matsumiya
authors.forename: Kensaku
authors.initials: K
authors.lastname: Matsuta
authors.forename: Mototsugu
authors.initials: M
authors.lastname: Mihara
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Watanabe