New facility for fundamental research in nuclear physics with polarized cold neutrons at PSI

A polarized neutron beam of 40 × 150 mm² cross-section and record intensity was formed by a unique optical system of 7 m length for fundamental physics research at the Swiss Spallation Neutron Source (SINQ) at the Paul Scherrer Institute in collaboration with Petersburg Nuclear Physics Institute and Institute for Particle Physics. The measured cold neutron flux density at the exit of the guide system was found to be 2 × 10⁸ n(cm² s mA)^-1. The routinely used proton current of SINQ is 1.2 mA. The mean polarization averaged over the spectrum was found to be 〈P〉 = 0.97. An optimization of geometrical parameters of the neutron guide system using numerical methods was made. Calculated flux neutron density and mean beam polarization, correspondingly, 1.6-1.8 × 10⁸ n(cm² s mA)^-1 and 0.975-0.98, are close to the measured values. High efficiency polarizing supermirrors with FeCo/TiZr coating are used in the multichannel polarizer. Ni/Ti supermirrors used in a beam condenser allow compressing the beam from 80 × 150 mm² to 40 × 150 mm² increasing the flux density by two times. Non-magnetic NiMo/Ti supermirrors were developed and used in the beam condenser for the first time. Neutron transparent quartz spacers provide perfect junctions between thin glass mirrors in the polarizer. A high efficiency (f = 0.99) adiabatic radio-frequency compact spin-flipper was installed.