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 $1.4 \cdot 10^7$ s$^{-1}$ to $1.6 \cdot 10^7$ 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.
Transport calculations for neutronic design require accurate nuclear data and validated computational tools. In the Spallation Physics Group, at the European Spallation Source, we perform shielding and neutron beam calculations to help the deployment of the instrument suite for the current high brilliance (top) moderator, as well for the design of the high intensity bottom moderator, currently under study for the facility. This work includes providing the best available nuclear data in addition to improving models and tools when necessary. In this paper we present the status of these activitie…
The European Spallation Source being constructed in Lund, Sweden will provide the user community with a neutron source of unprecedented brightness. By 2025, a suite of 15 instruments will be served by a high-brightness moderator system placed above the spallation target. The ESS infrastructure, consisting of the proton linac, the target station, and the instrument halls, allows for implementation of a second source below the spallation target. We propose to develop a second neutron source with a high-intensity moderator able to (1) deliver a larger total cold neutron flux, (2) provide high int…
The European Spallation Source is being constructed in Lund, Sweden and is planned to be the world's brightest pulsed spallation neutron source for cold and thermal neutron beams ($\le$ 1 eV). The facility uses a 2 GeV proton beam to produce neutrons from a tungsten target. The neutrons are then moderated in a moderator assembly consisting of both liquid hydrogen and water compartments. Surrounding the moderator are 22 beamports, which view the moderator's outside surfaces. The beamports are connected to long neutron guides that transport the moderated neutrons to the sample position via refle…
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 325000 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 dropp…
A fast-switching, high-repetition-rate magnet and power supply have been developed for and operated at TRIUMF, to deliver a proton beam to the new ultracold neutron (UCN) facility. The facility possesses unique operational requirements: a time-averaged beam current of 40~$μ$A with the ability to switch the beam on or off for several minutes. These requirements are in conflict with the typical operation mode of the TRIUMF cyclotron which delivers nearly continuous beam to multiple users. To enable the creation of the UCN facility, a beam-sharing arrangement with another facility was made. The b…
The TRIUMF ultracold advanced neutron (TUCAN) collaboration is a transpacific collaboration with the objective to measure the neutron electric dipole moment. We aim for an unprecedented sensitivity of $10^{-27}\,e$cm, an improvement by a factor of 30 over the current upper limit for this elusive quantity. To achieve this goal, we are planning a next-generation source for ultracold neutrons, based on a new, dedicated neutron spallation source at TRIUMF, liquid deuterium as cold moderator, and superfluid helium as ultracold-neutron converter. To operate at the full beam power of 20$\,$kW, a $^3$…
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 microA 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 microA, facilitating first large-scale UCN production in Canada.
Beryllium reflectors are used at spallation neutron sources in order to enhance the low-energy flux of neutrons emanating from the surface of a cold and thermal moderator. The design of such a moderator/reflector system is typically carried out using detailed Monte-Carlo simulations, where the beryllium reflector is assumed to behave as a poly-crystalline material. In reality, however, inhomogeneities in the beryllium could lead to discrepancies between the performance of the actual system when compared to the modeled system. The dependence of the total cross section in particular on crystalli…
A New High-Intensity Source for Ultracold Neutrons
Nagoya University（名古屋大学）；University of Manitoba（曼尼托巴大学）；TRIUMF（特里姆夫实验室）；Instituto de Física, Universidad Nacional Autónoma de México（墨西哥国立自治大学物理研究所）；University of Saskatchewan（萨斯喀彻温大学）；Simon Fraser University（西蒙菲莎大学）；The University of Winnipeg（温尼伯大学）；The University of British Columbia（不列颠哥伦比亚大学）；Department of Nuclear Engineering, Kyoto University（京都大学核工学科）；Institute for Integrated Radiation and Nuclear Science (KURNS), Kyoto University（京都大学综合辐射与核科学研究所（KURNS））；North Carolina State University（北卡罗来纳州立大学）
Neutronic Design and Measured Performance of the Low Energy Neutron Source (LENS) Target Moderator Reflector Assembly
低能中子源（英语：Low Energy Neutron Source，缩写LENS）是美国印第安纳大学回旋加速器实验室（英语：Indiana University Cyclotron Facility，缩写IUCF）正在建造的一个基于加速器的脉冲冷中子设施。LENS背后的想法是产生脉冲冷中子束，从Be中的（p，n）反应开始，其被缓和到meV能量，并从小立体角提取，用于中子仪器，其可以以相对宽（~1 msec）的中子脉冲宽度有效地操作。虽然这个源的功能和操作参数的组合是独一无二的，目前，中子设计具有几个功能类似于那些设想为未来的中子设施，如长脉冲中子源（LPSS）和非常冷的中子（VCN）源。我们描述的基本思想和设计细节的目标/减速器/反射器系统（TMR）和比较测量的亮度，能谱，和发射时间分布在不同的减速器配置与MCNP模拟。亮度测量使用环境温度水慢化剂同意MCNP模拟的测量精度在20%以内。从固体甲烷慢化剂测量的中子发射时间分布与模拟一致，冷中子通量是足够的材料的中子散射研究。我们描述了一些可能的修改现有的设计，这将增加冷中子的亮度，发射时间分布的影响可以忽略不计。
The European Spallation Source ESS is being constructed in Lund, Sweden, to be the world's brightest cold pulsed spallation neutron source. The facility uses a 2GeV proton beam hitting a target to produce neutrons. The neutrons are then thermalized in a moderator. Surrounding the moderator are several beam ports connected to neutron guides that transport the cold neutrons. Due to the long-pulse source nature of the ESS, neutron scattering instruments are significantly longer than at most existing facilities, with approximately half the instruments requiring neutron guides that are 150 meters l…
Neutron EDM Experiment with an Advanced Ultracold Neutron Source at TRIUMF
Kyoto University（京都大学）；Research Center for Nuclear Physics, the University of Osaka（大阪大学核物理研究中心）；The University of Manitoba（曼尼托巴大学）；TRIUMF（特利昂姆夫国家粒子加速器中心）；Instituto de Física, Universidad Nacional Autónoma de México（墨西哥国立自治大学物理研究所）；The University of Saskatchewan（萨斯喀彻温大学）；Simon Fraser University（西蒙菲莎大学）；The University of Winnipeg（温尼伯大学）
Initial results of the TRIUMF ultracold advanced neutron source
University of Manitoba（曼尼托巴大学）；TRIUMF（特柳姆弗国家粒子加速器中心）；Instituto de Física, Universidad Nacional Autónoma de México（墨西哥国立自治大学物理研究所）；University of Saskatchewan（萨斯喀彻温大学）；Simon Fraser University（西蒙菲莎大学）；The University of Winnipeg（温尼伯大学）；The University of British Columbia（不列颠哥伦比亚大学）；Department of Nuclear Engineering, Kyoto University（京都大学核工系）；Institute for Integrated Radiation and Nuclear Science (KURNS), Kyoto University（京都大学综合辐射与核科学研究所）；North Carolina State University（北卡罗来纳州立大学）；Research Center for Nuclear Physics (RCNP), The University of Osaka（大阪大学核物理研究中心）
The European Spallation Source (ESS), presently under construction in Lund, Sweden, is a multidisciplinary international laboratory that will operate the world's most powerful pulsed neutron source. Supported by a 3M Euro Research and Innovation Action within the EU Horizon 2020 program, a design study (HighNESS) is now underway to develop a second neutron source below the spallation target. Compared to the first source, located above the spallation target and designed for high cold and thermal brightness, the new source will provide higher intensity, and a shift to longer wavelengths in the s…
Pulsed beams have tremendous advantages for precision experiments with cold neutrons. In order to minimise and measure systematic effects, they are used at continuous sources in spite of the related substantial decrease in intensity. At the European Spallation Source ESS these experiments will profit from the pulse structure of the source and its 50 times higher peak brightness compared to the most intense reactor facilities, making novel concepts feasible. Therefore, the cold neutron beam facility for particle physics ANNI was proposed as part of the ESS instrument suite. The proposed design …
The NNBAR experiment for the European Spallation Source will search for free neutrons converting to antineutrons with a sensitivity improvement of three orders of magnitude compared to the last such search. This paper describes progress towards a conceptual design report for NNBAR. The design of a moderator, neutron reflector, beamline, shielding and annihilation detector is reported. The simulations used form part of a model which will be used for optimisation of the experiment design and quantification of its sensitivity.
Canada recently lost its major supply of neutron beams with the closure of the National Research Universal reactor at Chalk River Laboratories in March 2018. This issue is further exacerbated by the closure of other reactors abroad, which also served as centers for neutron research. Consequently, there is a demand for new sources, both for Canada and internationally, as the global supply shrinks. Compact accelerator driven neutron sources provide an avenue to realize an intense source of pulsed neutron beams, with a capital cost significantly lower than spallation sources. In an effort to clos…
