Neutron optics of the PSI ultracold-neutron source: characterization and simulation

The ultracold-neutron (UCN) source at the Paul Scherrer Institute serves mainly experiments in fundamental physics. High UCN intensities are the key for progress and success in such experiments. A detailed understanding of all source parameters is required for future improvements. Here we present the UCN source components, elements of the neutron optics, the characterization of important related parameters like emptying times, storage times and transmission probabilities of UCNs, which are ultimately defining the UCN intensity delivered at the beamports. We also introduce a detailed simulation model of the PSI UCN source, used to analyze the measurements and to extract surface parameters. This work illustrates the successful construction and operation of a large-scale facility delivering high UCN count rate. The observed characteristics of many neutron-optics parameters has been successfully simulated in a detailed Monte-Carlo model implemented in the MCUCN code.