Cryogenic Systems for the TUCAN EDM Experiment

¹ The University of Winnipeg, Winnipeg, MB, Canada
² University of Manitoba, Winnipeg, MB, Canada
³ TRIUMF, Vancouver, BC, Canada
⁴ Universidad Nacional Autónoma de México, Mexico City, Mexico
⁵ University of Saskatchewan, Saskatoon, SK, Canada
⁶ Department of Nuclear Engineering, Kyoto University, Kyoto, Japan
⁷ North Carolina State University, Raleigh, NC, USA
⁸ Institute for Integrated Radiation and Nuclear Science (KURNS), Kyoto University, Osaka, Japan
⁹ Research Center for Nuclear Physics (RCNP), Osaka University, Osaka, Japan
¹⁰ High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, Japan
¹¹ Nagoya University, Aichi, Japan
¹² The University of British Columbia, Vancouver, BC, Canada
¹³ The University of Northern BC, Prince George, BC, Canada
¹⁴ McGill University, Montreal, QC, Canada
¹⁵ Simon Fraser University, Burnaby, BC, Canada
¹⁶ Oak Ridge National Laboratory, Knoxville, TN, USA

^* e-mail: j.martin@uwinnipeg.ca
^** on behalf of the TUCAN Collaboration

Published online: 1 August 2025

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 × 10−27 ecm, 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 107 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.