Concepts of UCN sources for the FRM-II

Three concepts for sources of ultra-cold neutrons (UCN) for the reactor FRM-II at Garching near Munich are studied: one, Mini-D2, is a source with 170 cm3 of solid deuterium in the beam tube SR4 and the second one a large solid-deuterium source (volume about 30 dm3), mounted in the beam tube SR5 as an advanced cold source with a number of neutron guides. The third one, Mark 3000, uses superfluid 4He at a cold-neutron guide. A UCN density of up to 7×104 cm−3 may possibly be achieved in the storage volumes of Mini-D2 yielding more than 109 UCN for extraction to an attached experimental setup. The usable UCN flux at the periphery of the large deuterium source is predicted to be 2×107 cm−2 s−1. Mark 3000, finally, is expected to yield a UCN density of about 105 cm−3.