Coupled hydrogen moderator optimization with ortho/para hydrogen ratio

Kai, Tetsuya; Harada, Masahide; Teshigawara, Makoto; Watanabe, Noboru; Ikeda, Yujiro

doi:10.1016/j.nima.2003.11.427

Cited by 49 publications

(29 citation statements)

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“…The thermal MFP of 1cm causes the two hot spots in the volume moderator, at the target and reflector sides: thermal neutrons within about 1cm of the moderator edges are slowed down to cold energies. The total cross section is reduced by one order of magnitude for cold neutrons in para-H2, making it easier to extract neutrons from the whole volume of the moderator.A simple model based on this MFP difference reproduces quite well the angular emission of cold neutrons from a pure para-H2 disc-shaped moderator [134]. Thermal neutrons from the water pre-moderator are primarily slowed down to the cold regime by the first collision after entering the para-H2 close to the moderator wall, escaping the moderator volume as cold neutrons with a high probability of no further collision.…”

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confidence: 81%

“…However, ESS delivers bi-spectral neutron beams, also implementing a thermal neutron source. It is also advantageous to reduce the dimensions of the thermal moderator, since less beryllium reflector is removed for beam extraction, resulting in a lower brightness penalty.The brightness distribution from the surface of a volume moderator filled with pure para-H2 is non-uniform [134]. Figure 76 shows the calculated brightness distribution over the emitting surface of a 10cm tall moderator.…”

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confidence: 99%

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The European Spallation Source Design

et al. 2017

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The ESS Design: Accelerator 6The ESS Design: Target 66The ESS Design: Controls 93The ESS Design: Conventional Facilities 109Physica ScriptaPhys. Scr. 93 (2018) 014001 (121pp) https://doi.org/10. 1088/1402-4896/aa9bff This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercialNoDerivs 3.0 licence. Content from this work may be used under the terms of the Creative Commons Attribution-NonCommercialNoDerivs 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Neutron scattering is a well-developed and extensively used means to get access to fundamental properties of biological matter as well as of physical materials. Until the end of the twentieth century that was mainly practiced with-and limited in performance by-the continuous flux of neutrons from ageing nuclear reactors (e.g. the Institut Laue-Langevin (ILL), the flagship of neutron research in Europe and in the world) [1]). Looking forward to the following two decades, an OECD report published in 1998 diagnosed the foreseeable decrease of the number of operational facilities [2] and the need to progress in performance. Considering the high scientific interest and the increasing importance of the subject for society at large, the report concluded by strongly recommending the construction of next generation neutron sources in America, Europe and Asia. Pulsed spallation neutron sources (SNS) using a proton beam power exceeding 1 MW were specifically mentioned as the most interesting high performance facilities in the future landscape of neutron laboratories.The USA was the first country to follow this advice by building the SNS in the Oak Ridge National Laboratory (ORNL) which started in 2006 [3, 4]. Japan followed in 2009 with the Japan Proton Accelerator Research Centre (J-PARC) in Tokai [5,6]. In Europe, the subject was part of a concerted effort to further develop the European world-leading largescale research infrastructures suite. In 2003, the European Strategy Forum for Research Infrastructures (ESFRI), set up by the Research Ministries of the Member States and associated countries, concluded that a 5 MW long-pulse, single target station layout with nominally 22 'public' instruments was the optimum technical reference design for an European Spallation Source (ESS) that would meet the needs of the European science community in the second quarter of the century [7].Six years later, in 2009, it materialised in a real project with the adoption of the site of Lund (Sweden). A preconstruction phase followed until the end of 2013 during which the design was finalised [8]. Construction then started with the first neutron beams planned to be available in 2019, and the ESS facility to be operational at full performance in 2025.2 Description 2.1 Principle and specifics. The high level parameters of ESS are shown in table 1. As at SNS and J-PARC, neutrons at ESS are produced by spallation, when the 2 GeV protons hit the meta...

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The European Spallation Source Design

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“…This instrument is viewing the lower tier partially coupled hydrogen moderator. Moderator dimensions are 13 x 13 x 5cm 3 . A layout of the Lujan Mark-II target systems including its moderators is shown in figure 1.…”

Section: Methodsmentioning

confidence: 99%

“…Simulation calculations indicate that the neutronic performance of a liquid hydrogen moderator depends on the para-hydrogen concentration. [1][2][3] Also, it is shown in the experimental result that the neutron pulse peak intensities increase with the higher para hydrogen concentrations. [4] However, there is no experimental data of time dependent neutronic performance from a hydrogen moderator in the high radiation field.…”

Section: Introductionmentioning

confidence: 99%

Measurements of the change of neutronic performance of a hydrogen moderator at Manuel Lujan Neutron Scattering Center due to conversion from ortho- to para-hydrogen state

Ooi

Ichihara

Muhrer

et al. 2006

Nuclear Instruments and Methods in Physics Research Section A:

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The ortho/para hydrogen ratio is a key parameter for the neutronic performance of a liquid hydrogen moderator. In order to get a better understanding of the influence that the ortho/para-hydrogen ratio has on the performance of such a moderator, we measured the neutronic performance of the partially coupled liquid-hydrogen moderator at the LANSCE Manuel Lujan Jr. Neutron Scattering Center, Los Alamos, USA, as a function of time after condensation. This was done by measuring the energy spectra and pulse shapes (neutron emission time distributions) of this moderator. It was found that the neutronic characteristic of the moderator changes with the elapsed time after condensation, and that the changes were so significant that for any scattering experiment made on such a moderator, the effect should be carefully evaluated.Keyword: Pulsed neutron source, Hydrogen moderator, ortho-para conversion, energy spectrum, emission time distribution IntroductionAt 1 MW class high power spallation neutron sources, liquid hydrogen is at present a unique realistic candidate for a cold moderator material. Therefore, liquid hydrogen moderators have been adopted in the new high-power spallation neutron sources, JSNS (Japan Spallation Neutron Source) in Japan and SNS (Spallation Neutron Source) in the USA. Simulation calculations indicate that the neutronic performance of a liquid hydrogen moderator depends on the para-hydrogen concentration.[1-3] Also, it is shown in the experimental result that the neutron pulse peak intensities increase with the higher para hydrogen concentrations.[4] However, there is no experimental data of time dependent neutronic performance from a hydrogen moderator in the high radiation field. Such data would be of great benefit not only to new spallation neutron sources but also to existing neutron facilities.The Manuel Lujan Jr. Neutron Scattering Center has four water moderators and two liquid hydrogen moderators but there is no ortho-para conversion catalyst in the hydrogen loop. Therefore, it is expected that the para-hydrogen concentration in the loop will increase over time after liquefaction. The para hydrogen concentration in the state of equilibrium for hydrogen at T=20 K is 99.8%, whereas at T=300 K the equilibrium is 25% para hydrogen. Since the liquefaction process is significantly faster than the ortho-to-para conversion time without a catalyst at T=20K, the hydrogen loop at the Lujan Center always contains 25% para and 75% ortho-hydrogen right after a fresh filling. However, due to the different points of equilibrium for hydrogen at T=20K and at room temperature, a conversion from ortho to para hydrogen will start immediately. Even though the time constant for this process is fairly long, the ortho/para concentration and with it the neutronic performance will change during a typical period of operation (~10 days) at the Lujan Center. We have therefore measured the neutronic performance of the lower tier partially coupled liquid hydrogen moderator at the Lujan Center continuously for 132...

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“…Decoupled one is good for high resolution instrument with sharp pulse structure but sacrificing intensity. Poisoned decoupled moderator has a sharper pulse structure and less intensity, and it is used for extremely high resolution instrument such as very high resolution powder diffractometer [7]. The energy of neutron is commonly analyzed by the time-of-flight of neutrons going through a flight path in a pulsed neutron source.…”

Section: Some Performance Of Instruments [6]mentioning

confidence: 99%

Present Status of the Materials & Life Science Experimental Facility of J-PARC

Arai¹,

Futakawa²,

Tazaki³

et al. 2015

Proceedings of the 2nd International Symposium on Science at J-Parc — Unlocking the Mysteries of Life, Matter and the Universe

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The facility has resumed since 17th February 2014 after reformation of operation safety system required from the new regulation because of the accident in the Hadron Facility in May 2013. During eight-month shutdown period various hardware components have been improved; such as installation of additional RFQs in Linac to increase its energy to achieve higher power, repairing and replacement on the mercury (Hg) cooling loops of the neutron target, improvement on the cryogenic system for stable operation, etc. In order to mitigate the pitting damage on the Hg-target container we have been injecting helium micro bubbles in the target. The laser Doppler vibrometory showed us that vibration on the proton bombardment has been drastically reduced by the injection. Twenty one instruments have been already installed. Sixteen instruments are operated for user program and four instruments are under either commissioning or construction. Now the experimental hall is almost full with instruments, leaving only 2 ports available for the future use. Operational time for user program in JFY2014 was about 170 days, and we received more than 700 general experimental proposals from users. World-class scientific outputs have been being created in various scientific fields, ranging from Li-battery science to bio-molecular science. Since J-PARC is internationally open for users, we have got experimental proposals from abroad, which are more than 15% of the whole proposals. More than 20% of proposals have come from industries and a half of them are proprietary use. This fact has revealed a new horizon has come in the neutron scattering science in the 21 century.

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Coupled hydrogen moderator optimization with ortho/para hydrogen ratio

Cited by 49 publications

References 11 publications

The European Spallation Source Design

The European Spallation Source Design

Measurements of the change of neutronic performance of a hydrogen moderator at Manuel Lujan Neutron Scattering Center due to conversion from ortho- to para-hydrogen state

Present Status of the Materials & Life Science Experimental Facility of J-PARC

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