The PSI ultra-cold neutron source

A new type of ultra-cold neutron (UCN) source based on the spallation process is under construction at PSI. The essential elements are a pulsed proton beam with highest intensity (Ip≥2mA) and a low duty cycle (1%), a lead spallation target, a large D2OD2O moderator and a solid deuterium (sD2sD2) converter system. Spallation neutrons are thermalized in the D2OD2O, further cooled and partially downscattered into the ultra-cold neutron range in the sD2sD2. The expected UCN density is higher than 1000UCN/cm3 in typical experiments, an increase of almost two orders of magnitude over the best source currently available (at ILL). The new UCN source is expected to come into operation in 2009.