Cryogenic systems for the TUCAN EDM experiment

TL;DR

The paper describes the design, construction, and recent cryogenic milestones of the TUCAN ultracold neutron source, which uses superfluid helium at 1K to enable a highly precise neutron EDM experiment.

Contribution

It introduces the innovative superfluid helium-based UCN source for neutron EDM measurement and details the recent successful cooling and filling of the superfluid helium volume.

Findings

Superfluid helium volume successfully cooled and filled for the first time.

UCN production rate expected to exceed 10^7 UCN/s.

Cryogenic milestones achieved in the development of the source.

Abstract

The TUCAN (TRIUMF UltraCold Advanced Neutron) Collaboration is completing a new ultracold neutron (UCN) source. The UCN source will deliver UCNs to a neutron electric dipole moment (EDM) experiment. The EDM experiment is projected to be capable of an uncertainty of $1\times 10^{-27}~e$cm, competitive with other planned projects, and a factor of ten more precise than the present world's best. The TUCAN source is based on a UCN production volume of superfluid helium (He-II), held at 1~K, and coupled to a proton-driven spallation target. The production rate in the source is expected to be in excess of $10^7$~UCN/s; since UCN losses can be small in superfluid helium, this should allow us to build up a large number of UCNs. The spallation-driven superfluid helium technology is the principal aspect making the TUCAN project unique. The superfluid production volume was recently cooled, for the first time, and successfully filled with superfluid helium. The design principles of the UCN source are described, along with some of the challenging cryogenic milestones that were recently passed.