Speaker
Description
In 2011, a spallation neutron source dedicated solely to the production of ultracold neutrons (E_kin < 300 neV), referred to as UCN, began operation at the Paul Scherrer Institute (PSI), Switzerland.
The key feature of the facility is a cold moderator containing about 30 liters (~5 kg) of frozen deuterium kept at a temperature of 5 K. This ice block first moderates the thermal neutrons originating from the surrounding heavy water moderator and subsequently downscatters them into the ultracold regime. The neutrons are produced in a lead based spallation target that is very similar in design to the well established SINQ targets. Ultracold neutrons are produced during an 8 s long proton pulse delivered periodically every 300 s by PSI’s continuous wave proton accelerator HIPA. These neutrons are stored in a 1.6 m³ storage vessel and then delivered to the experiments.
The early operational phase showed that handling liquid deuterium — its para-ortho conversion, the filling process into the moderator vessel, and subsequent solidification — is a demanding procedure that required optimization over several years.
This presentation provides an overview of our solutions to some of the specific challenges associated with handling all three phases of deuterium. In addition, we report on our approach to mitigating frost build-up on the surface of the deuterium ice, which causes additional scattering losses of ultracold neutrons and therefore reduces their number available for experiments.
We have recently started a major refurbishment project aimed at repairing some faulty components which have emerged in recent years and, in parallel, further increasing the ultracold neutron yield. Many key components will be replaced. In particular, the design of the solid deuterium moderator vessel is undergoing a fundamental revision. A brief outline of this project is also included in the presentation.