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Charles Davis

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Petersburg Nuclear Physics Institute

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Papers by Charles Davis

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

arXiv (Cornell University), Dec 15, 2019

We report on our efforts to optimize the geometry of neutron moderators and converters for the TR... more 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 19.3 kW proton beam delivered by TRIUMF's 520 MeV cyclotron. Spallation neutrons will be moderated in heavy water at room temperature and in liquid deuterium at 20 K, and then superthermally converted to ultracold neutrons in superfluid, isotopically purified 4 He. The helium will be cooled by a 3 He fridge through a 3 He-4 He 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 27 L, achieving a production rate of 1.4 • 10 7 s −1 to 1.6 • 10 7 s −1 with a heat load of 8.1 W. At that heat load, the fridge can cool the superfluid helium to 1.1 K, resulting in a storage lifetime for ultracold neutrons in the source of about 30 s. 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 −27 e cm.

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

Nuclear Instruments and Methods in Physics Research, Apr 1, 2020

We report on our efforts to optimize the geometry of neutron moderators and converters for the TR... more 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 19.3 kW proton beam delivered by TRIUMF's 520 MeV cyclotron. Spallation neutrons will be moderated in heavy water at room temperature and in liquid deuterium at 20 K, and then superthermally converted to ultracold neutrons in superfluid, isotopically purified 4 He. The helium will be cooled by a 3 He fridge through a 3 He-4 He 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 27 L, achieving a production rate of 1.4 • 10 7 s −1 to 1.6 • 10 7 s −1 with a heat load of 8.1 W. At that heat load, the fridge can cool the superfluid helium to 1.1 K, resulting in a storage lifetime for ultracold neutrons in the source of about 30 s. 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 −27 e cm.

First ultracold neutrons produced at TRIUMF

Physical Review C, Feb 27, 2019

We installed a source for ultracold neutrons at a new, dedicated spallation target at TRIUMF. The... more We installed a source for ultracold neutrons at a new, dedicated spallation target at TRIUMF. The source was originally developed in Japan and uses a superfluid-helium converter cooled to 0.9 K. During an extensive test campaign in November 2017, we extracted up to 325 000 ultracold neutrons after a one-minute irradiation of the target, over three times more than previously achieved with this source. The corresponding ultracold-neutron density in the whole production and guide volume is 5.3 cm −3. The storage lifetime of ultracold neutrons in the source was initially 37 s and dropped to 24 s during the eighteen days of operation. During continuous irradiation of the spallation target, we were able to detect a sustained ultracold-neutron rate of up to 1500 s −1. Simulations of UCN production, UCN transport, temperature-dependent UCN yield, and temperature-dependent storage lifetime show excellent agreement with the experimental data and confirm that the ultracold-neutron-upscattering rate in superfluid helium is proportional to T 7 .

arXiv : A beamline for fundamental neutron physics at TRIUMF

This article describes the new primary proton beamline 1U at TRIUMF. The purpose of this beamline... more This article describes the new primary proton beamline 1U at TRIUMF. The purpose of this beamline is to produce ultracold neutrons (UCN) for fundamental-physics experiments. It delivers up to 40 µA of 480 MeV protons from the TRIUMF cyclotron to a tungsten spallation target and uses a fast kicker to share the beam between the Center for Molecular and Materials Science and UCN. The beamline has been successfully commissioned and operated with a beam current up to 10 µA, facilitating first large-scale UCN production in Canada.

Characterization of electroless nickel-phosphorus plating for ultracold-neutron storage

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

Electroless nickel plating is an established industrial process that provides a robust and relati... more Electroless nickel plating is an established industrial process that provides a robust and relatively low-cost coating suitable for transporting and storing ultracold neutrons (UCN). Using roughness measurements and UCN-storage experiments we characterized UCN guides made from polished aluminum or stainless-steel tubes plated by several vendors. All electroless nickel platings were similarly suited for UCN storage with an average loss probability per wall bounce of 2.8 • 10 −4 to 4.1 • 10 −4 for energies between 90 neV and 190 neV, or a ratio of imaginary to real Fermi potential η of 1.7 • 10 −4 to 3.3 • 10 −4. Measurements at different elevations indicate that the energy dependence of UCN losses is well described by the imaginary Fermi potential. Some special considerations are required to avoid an increase in surface roughness during the plating process and hence a reduction in UCN transmission. Increased roughness had only a minor impact on storage properties. Based on these findings we chose a vendor to plate the UCN-production vessel that will contain the superfluid-helium converter for the new TRIUMF UltraCold Advanced Neutron (TUCAN) source, achieving acceptable UCN-storage properties with η = 3.5(5) • 10 −4 .

Fast-switching magnet serving a spallation-driven ultracold neutron source

Physical Review Accelerators and Beams, 2019

$Research paper thumbnail of The first direct measurement of 17O(\alpha ,\gamma )21Ne and its impact upon s-process abundances$

The first direct measurement of 17O(\alpha ,\gamma )21Ne and its impact upon s-process abundances

Proceedings of 11th Symposium on Nuclei in the Cosmos — PoS(NIC XI), 2011

The first direct measurement of 17 O(α,γ) 21 Ne M. Taggart

A beamline for fundamental neutron physics at TRIUMF

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2019

This article describes the new primary proton beamline 1U at TRIUMF. The purpose of this beamline... more This article describes the new primary proton beamline 1U at TRIUMF. The purpose of this beamline is to produce ultracold neutrons (UCN) for fundamental-physics experiments. It delivers up to 40 µA of 480 MeV protons from the TRIUMF cyclotron to a tungsten spallation target and uses a fast kicker to share the beam between the Center for Molecular and Materials Science and UCN. The beamline has been successfully commissioned and operated with a beam current up to 10 µA, facilitating first large-scale UCN production in Canada.

TEST OF CHARGE SYMMETRY I N n-p ELASTIC SCATTERING AT 480 MeV +

Le Journal de Physique Colloques, 1985

The Precision nEDM Measurement with UltraCold Neutrons at TRIUMF

Proceedings of the 24th International Spin Symposium (SPIN2021)

The TRIUMF Ultra-Cold Advanced Neutron (TUCAN) collaboration aims at a precision neutron electric... more The TRIUMF Ultra-Cold Advanced Neutron (TUCAN) collaboration aims at a precision neutron electric dipole moment (nEDM) measurement with an uncertainty of 10 −27 e•cm, which is an orderof-magnitude better than the current nEDM upper limit and enables us to test Supersymmetry. To achieve this precision, we are developing a new high-intensity ultracold neutron (UCN) source using super-thermal UCN production in superfluid helium (He-II) and a nEDM spectrometer. The current development status of them is reported in this article.

Charge symmetry breaking in the reaction np → dπ0

Nuclear Physics A, 2000

ABSTRACT Charge Symmetry Breaking (CSB) in the strong interaction is due ultimately to the mass d... more ABSTRACT Charge Symmetry Breaking (CSB) in the strong interaction is due ultimately to the mass difference between the u and d quarks, but is described conveniently by meson-exchange models. TRIUMF experiment E704 measures the foreward-backward asymmetry (Afb) in np-&gt;dπ0, which must be zero in the centre-of-mass if charge symmetry is conserved. The angle-integrated value of Afb is calculated to be -35×10-4 near 280 MeV with the dominant contribution coming from (π0-η) and (π0-η&#39;) mixing. The experiment uses a neutron beam of 279.5 MeV, a liquid hydrogen target, and the SASP spectrometer to detect deuterons from the np-&gt;dπ0 reaction. A measurement of the pp-&gt;dπ+ distribution, for which Afb must be zero, provides a strong test of systematic errors.

A multi-cell target for ΛΛ hypernuclei searches

Nuclear Physics A, 1995

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

arXiv (Cornell University), Dec 15, 2019

We report on our efforts to optimize the geometry of neutron moderators and converters for the TR... more 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 19.3 kW proton beam delivered by TRIUMF's 520 MeV cyclotron. Spallation neutrons will be moderated in heavy water at room temperature and in liquid deuterium at 20 K, and then superthermally converted to ultracold neutrons in superfluid, isotopically purified 4 He. The helium will be cooled by a 3 He fridge through a 3 He-4 He 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 27 L, achieving a production rate of 1.4 • 10 7 s −1 to 1.6 • 10 7 s −1 with a heat load of 8.1 W. At that heat load, the fridge can cool the superfluid helium to 1.1 K, resulting in a storage lifetime for ultracold neutrons in the source of about 30 s. 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 −27 e cm.

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

Nuclear Instruments and Methods in Physics Research, Apr 1, 2020

We report on our efforts to optimize the geometry of neutron moderators and converters for the TR... more 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 19.3 kW proton beam delivered by TRIUMF's 520 MeV cyclotron. Spallation neutrons will be moderated in heavy water at room temperature and in liquid deuterium at 20 K, and then superthermally converted to ultracold neutrons in superfluid, isotopically purified 4 He. The helium will be cooled by a 3 He fridge through a 3 He-4 He 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 27 L, achieving a production rate of 1.4 • 10 7 s −1 to 1.6 • 10 7 s −1 with a heat load of 8.1 W. At that heat load, the fridge can cool the superfluid helium to 1.1 K, resulting in a storage lifetime for ultracold neutrons in the source of about 30 s. 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 −27 e cm.

First ultracold neutrons produced at TRIUMF

Physical Review C, Feb 27, 2019

We installed a source for ultracold neutrons at a new, dedicated spallation target at TRIUMF. The... more We installed a source for ultracold neutrons at a new, dedicated spallation target at TRIUMF. The source was originally developed in Japan and uses a superfluid-helium converter cooled to 0.9 K. During an extensive test campaign in November 2017, we extracted up to 325 000 ultracold neutrons after a one-minute irradiation of the target, over three times more than previously achieved with this source. The corresponding ultracold-neutron density in the whole production and guide volume is 5.3 cm −3. The storage lifetime of ultracold neutrons in the source was initially 37 s and dropped to 24 s during the eighteen days of operation. During continuous irradiation of the spallation target, we were able to detect a sustained ultracold-neutron rate of up to 1500 s −1. Simulations of UCN production, UCN transport, temperature-dependent UCN yield, and temperature-dependent storage lifetime show excellent agreement with the experimental data and confirm that the ultracold-neutron-upscattering rate in superfluid helium is proportional to T 7 .

arXiv : A beamline for fundamental neutron physics at TRIUMF

This article describes the new primary proton beamline 1U at TRIUMF. The purpose of this beamline... more This article describes the new primary proton beamline 1U at TRIUMF. The purpose of this beamline is to produce ultracold neutrons (UCN) for fundamental-physics experiments. It delivers up to 40 µA of 480 MeV protons from the TRIUMF cyclotron to a tungsten spallation target and uses a fast kicker to share the beam between the Center for Molecular and Materials Science and UCN. The beamline has been successfully commissioned and operated with a beam current up to 10 µA, facilitating first large-scale UCN production in Canada.

Characterization of electroless nickel-phosphorus plating for ultracold-neutron storage

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

Electroless nickel plating is an established industrial process that provides a robust and relati... more Electroless nickel plating is an established industrial process that provides a robust and relatively low-cost coating suitable for transporting and storing ultracold neutrons (UCN). Using roughness measurements and UCN-storage experiments we characterized UCN guides made from polished aluminum or stainless-steel tubes plated by several vendors. All electroless nickel platings were similarly suited for UCN storage with an average loss probability per wall bounce of 2.8 • 10 −4 to 4.1 • 10 −4 for energies between 90 neV and 190 neV, or a ratio of imaginary to real Fermi potential η of 1.7 • 10 −4 to 3.3 • 10 −4. Measurements at different elevations indicate that the energy dependence of UCN losses is well described by the imaginary Fermi potential. Some special considerations are required to avoid an increase in surface roughness during the plating process and hence a reduction in UCN transmission. Increased roughness had only a minor impact on storage properties. Based on these findings we chose a vendor to plate the UCN-production vessel that will contain the superfluid-helium converter for the new TRIUMF UltraCold Advanced Neutron (TUCAN) source, achieving acceptable UCN-storage properties with η = 3.5(5) • 10 −4 .

Fast-switching magnet serving a spallation-driven ultracold neutron source

Physical Review Accelerators and Beams, 2019

$Research paper thumbnail of The first direct measurement of 17O(\alpha ,\gamma )21Ne and its impact upon s-process abundances$

The first direct measurement of 17O(\alpha ,\gamma )21Ne and its impact upon s-process abundances

Proceedings of 11th Symposium on Nuclei in the Cosmos — PoS(NIC XI), 2011

The first direct measurement of 17 O(α,γ) 21 Ne M. Taggart

A beamline for fundamental neutron physics at TRIUMF

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2019

This article describes the new primary proton beamline 1U at TRIUMF. The purpose of this beamline... more This article describes the new primary proton beamline 1U at TRIUMF. The purpose of this beamline is to produce ultracold neutrons (UCN) for fundamental-physics experiments. It delivers up to 40 µA of 480 MeV protons from the TRIUMF cyclotron to a tungsten spallation target and uses a fast kicker to share the beam between the Center for Molecular and Materials Science and UCN. The beamline has been successfully commissioned and operated with a beam current up to 10 µA, facilitating first large-scale UCN production in Canada.

TEST OF CHARGE SYMMETRY I N n-p ELASTIC SCATTERING AT 480 MeV +

Le Journal de Physique Colloques, 1985

The Precision nEDM Measurement with UltraCold Neutrons at TRIUMF

Proceedings of the 24th International Spin Symposium (SPIN2021)

The TRIUMF Ultra-Cold Advanced Neutron (TUCAN) collaboration aims at a precision neutron electric... more The TRIUMF Ultra-Cold Advanced Neutron (TUCAN) collaboration aims at a precision neutron electric dipole moment (nEDM) measurement with an uncertainty of 10 −27 e•cm, which is an orderof-magnitude better than the current nEDM upper limit and enables us to test Supersymmetry. To achieve this precision, we are developing a new high-intensity ultracold neutron (UCN) source using super-thermal UCN production in superfluid helium (He-II) and a nEDM spectrometer. The current development status of them is reported in this article.

Charge symmetry breaking in the reaction np → dπ0

Nuclear Physics A, 2000

ABSTRACT Charge Symmetry Breaking (CSB) in the strong interaction is due ultimately to the mass d... more ABSTRACT Charge Symmetry Breaking (CSB) in the strong interaction is due ultimately to the mass difference between the u and d quarks, but is described conveniently by meson-exchange models. TRIUMF experiment E704 measures the foreward-backward asymmetry (Afb) in np-&gt;dπ0, which must be zero in the centre-of-mass if charge symmetry is conserved. The angle-integrated value of Afb is calculated to be -35×10-4 near 280 MeV with the dominant contribution coming from (π0-η) and (π0-η&#39;) mixing. The experiment uses a neutron beam of 279.5 MeV, a liquid hydrogen target, and the SASP spectrometer to detect deuterons from the np-&gt;dπ0 reaction. A measurement of the pp-&gt;dπ+ distribution, for which Afb must be zero, provides a strong test of systematic errors.

A multi-cell target for ΛΛ hypernuclei searches

Nuclear Physics A, 1995