Cryogenic design for a high intensity ultracold neutron source at TRIUMF

The TUCAN (TRIUMF Ultra-Cold Advanced Neutron) collaboration has been developing a source of high-intensity ultra-cold neutrons for use in a neutron electric dipole search. The source is composed of a spallation neutron source and a superfluid helium ultra-cold neutron converter, surrounded by a cold moderator. The temperature of the superfluid helium needs to be maintained at approximately 1.0 K to suppress up-scattering by phonons. The Kapitza conductance and the heat transport by the superfluid helium are key parameters which need to be well characterized. We have therefore investigated them in first experiments. Current efforts are directed at optimizing the design of the helium cryostat.