Considerations for an Intense Source of Ultracold Neutrons at the European Long Pulse Spallation Source

While intense reactor based sources of ultra-cold neutrons have been in operation for approximately three decades, it is only in the last few years that practical sources of UCN have been realized at spallation sources. Existing and proposed spallation based UCN sources employ two distinct strategies. In the first, the UCN converter (superfluid 4He, or solid D2) is placed in the immediate vicinity of the spallation target. In the second, a converter (usually superfluid He) is placed at the output end of a cold neutron guide fed by the spallation target cold source. Both of these approaches are considered in relation to the European Long Pulse Spallation Source.