Ultra-cold neutrons at PSI

A powerful pulsed Spallation Ultra-cold Neutron Source (SUNS) is being built by our collaboration at the Paul Scherrer Institut in Villigen, Switzerland. The source concept is based on the three step process of neutron production, moderation and conversion. A several seconds long pulse of the full (2 mA, 590 MeV) proton beam produces neutrons on a spallation target. After moderation in heavy water and cooling in solid deuterium part of the neutrons is converted into UCN. UCN are extracted upwards into a Be coated intermediate storage trap. Test experiments and calculations based upon them predict UCN densities of about 3000 cm-3 in a 2 m3 volume. UCN can be provided either in parallel to several small experiments or to a single setup which uses the full intensity. The system can he operated on a 1 % duty cycle, i.e. with 8 s long proton beam pulses followed by 800 s long periods without proton beam. The UCN lifetimes in the storage trap will exceed 500 s and thus fit to the macro-pulse scheme. The full UCN intensity will be used for a new experiment searching for a finite electric dipole moment of the neutron. This experiment aims at an 2 orders of magnitude improvement, in sensitivity as compared to current experiments. (author)