Optimizing neutron moderators for a spallation-driven ultracold-neutron source at TRIUMF

W. Schreyer; C. A. Davis; S. Kawasaki; T. Kikawa; C. Marshall; K. Mishima; T. Okamura; R. Picker

doi:10.1016/j.nima.2020.163525

Optimizing neutron moderators for a spallation-driven ultracold-neutron source at TRIUMF

W. Schreyer, C. A. Davis, S. Kawasaki, T. Kikawa, C. Marshall, K. Mishima, T. Okamura, R. Picker

Neutron Symmetries

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Abstract

We report on our efforts to optimize the geometry of neutron moderators and converters for the TRIUMF UltraCold Advanced Neutron (TUCAN) source using MCNP simulations. It will use an existing spallation neutron source driven by a 19.3kW proton beam delivered by TRIUMF's 520MeV cyclotron. Spallation neutrons will be moderated in heavy water at room temperature and in liquid deuterium at 20K, and then superthermally converted to ultracold neutrons in superfluid, isotopically purified ⁴He. The helium will be cooled by a ³He fridge through a ³He–⁴He heat exchanger. The optimization took into account a range of engineering and safety requirements and guided the detailed design of the source. The predicted ultracold-neutron density delivered to a typical experiment is maximized for a production volume of 27L, achieving a production rate of 1.4 ⋅ 10⁷s⁻¹ to 1.6 ⋅ 10⁷s⁻¹ with a heat load of 8.1W. At that heat load, the fridge can cool the superfluid helium to 1.1K, resulting in a storage lifetime for ultracold neutrons in the source of about 30s. The most critical performance parameters are the choice of cold moderator and the volume, thickness, and material of the vessel containing the superfluid helium. The source is scheduled to be installed in 2021 and will enable the TUCAN collaboration to measure the electric dipole moment of the neutron with a sensitivity of 10⁻²⁷ecm.

Original language	English
Article number	163525
Journal	Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Volume	959
DOIs	https://doi.org/10.1016/j.nima.2020.163525
State	Published - Apr 11 2020

Funding

We would like to thank P. Carlson and M. Chin for their early contributions to this work and Y.-S. Cho for providing an MCNP scattering kernel for polycrystalline bismuth. This work was supported by the Canada Fund for Innovation (CFI), the Natural Sciences and Engineering Research Council of Canada (NSERC), and Compute Canada.

Keywords

Moderator
Spallation
Superfluid helium
Ultracold neutrons

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10.1016/j.nima.2020.163525

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Schreyer, W., Davis, C. A., Kawasaki, S., Kikawa, T., Marshall, C., Mishima, K., Okamura, T., & Picker, R. (2020). Optimizing neutron moderators for a spallation-driven ultracold-neutron source at TRIUMF. Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 959, Article 163525. https://doi.org/10.1016/j.nima.2020.163525

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abstract = "We report on our efforts to optimize the geometry of neutron moderators and converters for the TRIUMF UltraCold Advanced Neutron (TUCAN) source using MCNP simulations. It will use an existing spallation neutron source driven by a 19.3kW proton beam delivered by TRIUMF's 520MeV cyclotron. Spallation neutrons will be moderated in heavy water at room temperature and in liquid deuterium at 20K, and then superthermally converted to ultracold neutrons in superfluid, isotopically purified 4He. The helium will be cooled by a 3He fridge through a 3He–4He heat exchanger. The optimization took into account a range of engineering and safety requirements and guided the detailed design of the source. The predicted ultracold-neutron density delivered to a typical experiment is maximized for a production volume of 27L, achieving a production rate of 1.4 ⋅ 107s−1 to 1.6 ⋅ 107s−1 with a heat load of 8.1W. At that heat load, the fridge can cool the superfluid helium to 1.1K, resulting in a storage lifetime for ultracold neutrons in the source of about 30s. The most critical performance parameters are the choice of cold moderator and the volume, thickness, and material of the vessel containing the superfluid helium. The source is scheduled to be installed in 2021 and will enable the TUCAN collaboration to measure the electric dipole moment of the neutron with a sensitivity of 10−27ecm.",

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Schreyer, W, Davis, CA, Kawasaki, S, Kikawa, T, Marshall, C, Mishima, K, Okamura, T & Picker, R 2020, 'Optimizing neutron moderators for a spallation-driven ultracold-neutron source at TRIUMF', Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, vol. 959, 163525. https://doi.org/10.1016/j.nima.2020.163525

Optimizing neutron moderators for a spallation-driven ultracold-neutron source at TRIUMF. / Schreyer, W.; Davis, C. A.; Kawasaki, S. et al.
In: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 959, 163525, 11.04.2020.

Research output: Contribution to journal › Article › peer-review

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T1 - Optimizing neutron moderators for a spallation-driven ultracold-neutron source at TRIUMF

AU - Schreyer, W.

AU - Davis, C. A.

AU - Kawasaki, S.

AU - Kikawa, T.

AU - Marshall, C.

AU - Mishima, K.

AU - Okamura, T.

AU - Picker, R.

PY - 2020/4/11

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N2 - We report on our efforts to optimize the geometry of neutron moderators and converters for the TRIUMF UltraCold Advanced Neutron (TUCAN) source using MCNP simulations. It will use an existing spallation neutron source driven by a 19.3kW proton beam delivered by TRIUMF's 520MeV cyclotron. Spallation neutrons will be moderated in heavy water at room temperature and in liquid deuterium at 20K, and then superthermally converted to ultracold neutrons in superfluid, isotopically purified 4He. The helium will be cooled by a 3He fridge through a 3He–4He heat exchanger. The optimization took into account a range of engineering and safety requirements and guided the detailed design of the source. The predicted ultracold-neutron density delivered to a typical experiment is maximized for a production volume of 27L, achieving a production rate of 1.4 ⋅ 107s−1 to 1.6 ⋅ 107s−1 with a heat load of 8.1W. At that heat load, the fridge can cool the superfluid helium to 1.1K, resulting in a storage lifetime for ultracold neutrons in the source of about 30s. The most critical performance parameters are the choice of cold moderator and the volume, thickness, and material of the vessel containing the superfluid helium. The source is scheduled to be installed in 2021 and will enable the TUCAN collaboration to measure the electric dipole moment of the neutron with a sensitivity of 10−27ecm.

AB - We report on our efforts to optimize the geometry of neutron moderators and converters for the TRIUMF UltraCold Advanced Neutron (TUCAN) source using MCNP simulations. It will use an existing spallation neutron source driven by a 19.3kW proton beam delivered by TRIUMF's 520MeV cyclotron. Spallation neutrons will be moderated in heavy water at room temperature and in liquid deuterium at 20K, and then superthermally converted to ultracold neutrons in superfluid, isotopically purified 4He. The helium will be cooled by a 3He fridge through a 3He–4He heat exchanger. The optimization took into account a range of engineering and safety requirements and guided the detailed design of the source. The predicted ultracold-neutron density delivered to a typical experiment is maximized for a production volume of 27L, achieving a production rate of 1.4 ⋅ 107s−1 to 1.6 ⋅ 107s−1 with a heat load of 8.1W. At that heat load, the fridge can cool the superfluid helium to 1.1K, resulting in a storage lifetime for ultracold neutrons in the source of about 30s. The most critical performance parameters are the choice of cold moderator and the volume, thickness, and material of the vessel containing the superfluid helium. The source is scheduled to be installed in 2021 and will enable the TUCAN collaboration to measure the electric dipole moment of the neutron with a sensitivity of 10−27ecm.

KW - Moderator

KW - Spallation

KW - Superfluid helium

KW - Ultracold neutrons

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ER -

Optimizing neutron moderators for a spallation-driven ultracold-neutron source at TRIUMF

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