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

Schreyer, W.; Davis, Charles A.; Kawasaki, S.; Kikawa, T.; Marshall, C.; Mishima, Kenji; Okamura, Takahiro; Picker, R.

doi:10.1016/j.nima.2020.163525

Cited by 15 publications

(6 citation statements)

References 39 publications

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“…The most prominent example is the search for a permanent electric dipole moment of the neutron (nEDM) [ 2 – 10 ]. The best achieved sensitivity for such experiments is limited by counting statistics, and efforts are made worldwide to develop new UCN sources to provide higher intensities [ 11 – 13 ]. Besides a high source yield, a highly optimized neutron transport to beamports and experiments is a key ingredient to the performance of UCN sources.…”

Section: Introductionmentioning

confidence: 99%

Ultracold neutron storage and transport at the PSI UCN source

et al. 2022

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Efficient neutron transport is a key ingredient to the performance of ultracold neutron (UCN) sources, important to meeting the challenges placed by high precision fundamental physics experiments. At the Paul Scherrer Institute’s UCN source we have been continuously improving our understanding of the UCN source parameters by performing a series of studies to characterize neutron production and moderation, and UCN production, extraction, and transport efficiency to the beamport. The present study on the absolute UCN transport efficiency completes our previous publications. We report on complementary measurements, namely one on the height-dependent UCN density and a second on the transmission of a calibrated quantity of UCN over a $$\sim 16$$ ∼ 16 m long UCN guide section connecting one beamport via the source storage vessel to another beamport. These allow us quantifying and optimizing the performance of the guide system based on extensive Monte Carlo simulations.

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Section: Introductionmentioning

confidence: 99%

Ultracold neutron storage and transport at the PSI UCN source

et al. 2022

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“…Here, cold neutrons can excite phonons and rotons, losing almost all their energy in the process to become ultracold. We estimate a total UCN production rate of 1.4 × 10 7 UCN/s at a proton current of 40 µA [8]. The reverse scattering, where a UCN gains momentum by scattering on existing rotons and phonons, is suppressed by cooling the medium.…”

Section: Ucn Productionmentioning

confidence: 97%

“…1. These moderators surround a vessel filled with superfluid, isotopically-purified helium-4 at around 1.1 K. The geometry has been optimized to create a large flux of cold neutrons inside the helium [8]. Here, cold neutrons can excite phonons and rotons, losing almost all their energy in the process to become ultracold.…”

Section: Ucn Productionmentioning

confidence: 99%

Estimated performance of the TRIUMF ultracold neutron source and electric dipole moment apparatus

Sidhu

Schreyer²,

Vanbergen³

et al. 2023

EPJ Web Conf.

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Searches for the permanent electric dipole moment of the neutron (nEDM) provide strong constraints on theories beyond the Standard Model of particle physics. The TUCAN collaboration is constructing a source for ultra-cold neutrons (UCN) and an apparatus to search for the nEDM at TRIUMF, Vancouver, Canada. In this work, we estimate that the spallation-driven UCN source based on a superfluid helium converter will provide (1.38 ± 0.02) 107 polarized UCN at a density of 217 ± 3 UCN/cm3 to a room-temperature EDM experiment per fill. With (1.43 ± 0.02) 106 neutrons detected after the Ramsey cycle, the statistical sensitivity for an nEDM search per storage cycle will be (1.94 ± 0.06) × 10−25 ecm (1σ). The goal sensitivity of 10−27 ecm (1σ) can be reached within 281 ± 16 measurement days.

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“…[6], and is currently installing experimental equipment at TRIUMF. The experimental plan is to produce UCN at a rate of 1.4 × 10 7 s −1 [16] by combining a spallation neutron source and a super-thermal converter of superfluid helium. The UCN source will be connected to an nEDM cell by UCN guide tubes with a total length of 12 m, and the cell will be filled with polarized UCN to a density of about 200 cm −3 at the beginning of the measurement [17].…”

Section: Introductionmentioning

confidence: 99%

A diffuse scattering model of ultracold neutrons on wavy surfaces

S.¹,

H.²,

Hatanaka³

et al. 2023

Preprint

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Metal tubes plated with nickel-phosphorus are used in many fundamental physics experiments using ultracold neutrons (UCN) because of their ease of fabrication. These tubes are usually polished to a average roughness of 25-150 nm. However, there is no scattering model that accurately describes UCN scattering on such a rough guide surface with a mean-square roughness larger than 5 nm. We therefore developed a scattering model for UCN in which scattering from random surface waviness with a size larger than the UCN wavelength is described by a microfacet Bidirectional Reflectance Distribution Function model (mf-BRDF model), and scattering from smaller structures by the Lambert's cosine law (Lambert model). For the surface waviness, we used the statistical distribution of surface slope measured by an atomic force microscope on a sample piece of guide tube as input of the model. This model was used to describe UCN transmission experiments conducted at the pulsed UCN source at J-PARC. In these experiments, a UCN beam collimated to a divergence angle smaller than ±6 • was directed into a guide tube with a mean-square roughness of 6.4 nm to 17 nm at an oblique angle, and the UCN transport performance and its time-of-flight distribution were measured while changing the angle of incidence. The mf-BRDF model combined with the Lambert model with scattering probability pL = 0.039 ± 0.003 reproduced the experimental results well. We have thus established a procedure to evaluate the characteristics of UCN guide tubes with a surface roughness of approximately 10 nm.

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

Cited by 15 publications

References 39 publications

Ultracold neutron storage and transport at the PSI UCN source

Ultracold neutron storage and transport at the PSI UCN source

Estimated performance of the TRIUMF ultracold neutron source and electric dipole moment apparatus

A diffuse scattering model of ultracold neutrons on wavy surfaces

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