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IOP conference series / Materials science and engineering 1240(1), 012117 - (2022). doi:10.1088/1757-899X/1240/1/012117, The Cryogenic Moderator System (CMS) is equipped with a catalyst to convert hydrogen from the ortho state to the para state, to keep desirably high parahydrogen fractions in the cold moderators, which is required to deliver a high brightness cold neutron beams to the scientific instruments using neutron scattering. An in-situ measurement system for the ortho and para fractions of liquid hydrogen (OPMS) where a Raman spectroscopy will be used is being developed. The required measurement precision is 0.1% to detect an undesirable shift towards a high orthohydrogen fraction caused by neutron scattering driven para-to-ortho back conversion. The dedicated OPMS sampling line has been designed and is placed in a bypass line from and to the CMS to minimize the hydrogen inventory and to make it physically isolated from the CMS if a sapphire window failure happens. Accident analysis for a hydrogen leak due to the sapphire window failure was carried out using an inhouse-developed simulation code, and the required safety relief size has been determined., Published by Institute of Physics, London [u.a.]

The neutron yield of a compact accelerator driven neutron source depends strongly on the target performance. This performance is influenced by the target composition and geometry, the cooling system design and which primary particles are used. We show that the temperature difference inside the target depends directly on the target thickness determined by the ion stopping range and therefore on the type and energy of the primary particle. Deuterons with a larger stopping power show a smaller temperature difference inside the target than protons allowing thus for a better target cooling.

Organic aromatic cold neutron moderators - like mesitylene ( C 9 H 12 ) - are often much more convenient to handle and to commission than cryogenic methane or ortho/para hydrogen moderators. Although this benefit comes at the cost of reduced brilliance, mesitylene moderators are suited to enable cold neutron applications at sources where a complex traditional cold moderator system is not feasible. Developing the Julich High Brilliance neutron Source (HBS) project, we have investigated the use of such a low-dimensional mesitylene moderator with MCNP and ANSYS simulations and validated the simulations with experiments at TU Dresden's AKR-2 reactor. Here we will document the feasibility, advantages and drawbacks of such a system and give an outlook on future optimization potentials.

Journal of neutron research 22(2-3), 109 - 118 (2020). doi:10.3233/JNR-200155, In the development of the European Spallation Source, the engineering phase of the Neutron Beam Extraction System is approaching its end. Currently, prototyping is ongoing to verify and increase the understanding of the manufacturing limitations in relation to the engineering aspects and beam extraction requirements from the instruments. After that the manufacturing of the suite of 16 neutron beam port inserts (NBPI) and light shutter systems (LSS) are phased into final detail design and manufacturing. The NBPIs have been developed as a close collaboration between ESS’ instruments design coordinators and intricately integrate a set of copper optics within a controlled atmosphere within the target monolith pressure vessel. The NBPIs therefore includes not only a processed atmosphere but also enables fine alignment of the optics assemblies within it, but also includes a system for inserting it into a very precisely aligned and measured position. Outside the NBPIs, along the neutron beam paths, sits the Neutron Beam Windows and sequentially, the LSS which incorporates an optical bridge beam guide before the beam enters the bunker area and the individual instrument beam transports. ESS have chosen the concept of LSS, which generates demanding requirements for alignment of moving shutter parts. These system parts are placed in the bunker area and bunker basement, areas that are partly accessible during maintenance periods., Published by IOS Press, Amsterdam

[8th International Meeting of the Union for Compact Accelerator-driven Neutron Sources, UCANS-8, 2019-07-08 - 2019-07-10, Paris, France] 8th International Meeting of the Union for Compact Accelerator-driven Neutron Sources, UCANS-8, Paris, France, 8 Jul 2019 - 10 Jul 2019; Les Ulis : EDP Sciences, The European physical journal / Web of Conferences Web of Conferences : proceedings proceedings 231, 04001 pp. (2020). doi:10.1051/epjconf/202023104001, Published by EDP Sciences, Les Ulis

IOP conference series / Materials science and engineering 755(1), 012101 - (2020). doi:10.1088/1757-899X/755/1/012101, The Cryogenic Moderator System (CMS) has been designed to cool high-energy neutrons down to cold neutrons in two cryogenic hydrogen moderators (four ones in the future) by forced flow of subcooled liquid hydrogen at 17 K and 1.0 MPa. At 5 MW proton beam power, an estimated nuclear heating of 6.7 kW (17.3 kW in the future) is generated in the moderators. The subcooled liquid hydrogen is circulated by two pumps arranged in series with a mass flow rate of 1 kg/s to maintain the average temperature rise over each moderator below 3 K and is cooled through a plate fin heat exchanger by a helium refrigerator with a cooling capacity of 30.3 kW at 15 K. The ESS moderator vessels are optimized for maximum cold neutron brightness and pure para-hydrogen, requiring a para concentration of > 99.5 %. An ortho-para-hydrogen convertor is integrated into the loop along with an online para-hydrogen measurement system. The pressure fluctuation caused by unpredictable abrupt changes of nuclear heating will be mitigated using a pressure control buffer with a volume of 65 1., Published by Institute of Physics, London [u.a.]

Journal of physics / Conference Series 1021, 012054 - (2018). doi:10.1088/1742-6596/1021/1/012054, The neutron Irradiation Module at the European Spallation Source will make use of the high intensity fast neutron spectrum to study the behaviour of the materials used in the facility, set within the ESS research and development program for the target station. By studying how these materials are affected by radiation, estimates of the material degradation in irrradiated bespoke samples will allow to optimise of the design and lifetime of regularly replaced target components. The general design and a set of results from the neutronics calculations, aimed at estimating proton and neutron flux distributions, displacement damage, heat deposition and activation for the radiological hazard analysis of the Irradiation Module, set within the Italian contributions to the ESS construction phase, are reported., Published by IOP Publ., Bristol

Journal of physics / Conference Series 1021, 012069 - (2018). doi:10.1088/1742-6596/1021/1/012069, The European Spallation Source (ESS) will be a 5 MW class spallation neutron research facility. An important part of the target station is the Moderator and Reflector (MR) System including structure and handling. The primary function of the MR Plugs is to efficiently reflect and moderate fast neutrons from the spallation target to thermal and cold neutrons suitable for the neutron scattering systems. However, the MR System need to fulfil many operational functions as well, which include cooling of radiation heat in liquid and metal bodies, positioning and structural support, capability of handling of active components and confinement, shielding and avoidance of streaming. Depending on the design, the accumulated neutron flux and irradiation induced material degradation mechanism limit the lifetime of the MR Plug. At full beam power of 5 MW, the MR Plugs need to be changed yearly. That imposes high demands on logistics, manufacturing and handling on the system. This paper presents the lifetime criteria of the MR System, in view of radiation induced material degradation. The complete MR System lifecycle is presented, which ranges from purchase of raw materials (aluminium alloy, stainless steel and beryllium), manufacturing, factory acceptance test FAT), transport, delivery control, pre-installation test until a new MR System is ready for installation., Published by IOP Publ., Bristol

IOP conference series / Materials science and engineering 502, 012161 - (2019). doi:10.1088/1757-899X/502/1/012161, For the majority of low temperature hydrogen applications the ortho- to parahydrogen (o-p-H2) spin configuration plays a vital role. Examples are liquid storage (heat of conversion) or neutron moderation (unequal cross section). Decreasing temperatures below ambient imply higher equilibrium p-H2 ratios. Often, rapid conversion close to the equilibrium is beneficial. The rather slow natural conversion can be sped up for example by catalytic contact to paramagnetic substances. For this, the paper gives an overview on published isothermal conversion catalyst data at LN2 temperature. Furthermore, an enhanced Catalyst Test Cryostat (CTC) facilitating new adiabatic and isothermal o-p-H2 catalyst conversion measurements is presented. Precise concentration determination is decisive. Hence, two commercial analyzers, essential for isothermal conversion measurements, using speed of sound or thermal conductivity will be compared to the performance of the independent adiabatic CTC results. Obtained activity data on an industrial catalyst at ≈77.3 K will be provided. Finally, a novel process, batch and closed cycle, providing mixtures with p-H2 contents ranging from 0.25 to ≈1.00 is introduced. The latter enables e.g. neutron moderation at stable, non-equilibrium o-p-H2 ratios., Published by Institute of Physics, London [u.a.]

With the construction of the European Spallation Source ESS, the European neutron user community is looking forward to the brightest source worldwide. At the same time there is an ongoing concentration of research with neutrons to only a few but very powerful neutron facilities. Responding to this situation the Julich Centre for Neutron Science has initiated a project for a compact accelerator driven high-brilliance neutron source, optimized for neutron scattering on small samples and to be realized at reasonable costs. The project deals with the optimization of potential projectiles, target and moderator concepts, versatile accelerator systems, cold sources, beam extraction systems and optimized instrumentation. A brief outline of the project, the achievements already reached, will be presented, as well as a vision for the future neutron landscape in Europe.

ADVANCES IN CRYOGENIC ENGINEERING: Transactions of the Cryogenic Engineering Conference - CEC, Anchorage, Alaska; AIP conference proceedings 1573(1), 659–664 (2014). doi:10.1063/1.4860765, The European Spallation Source (ESS), Lund, Sweden will be a 5MW long-pulse neutron spallation research facility and will enable new opportunities for researchers in the fields of life sciences, energy, environmental technology, cultural heritage and fundamental physics. Neutrons are produced by accelerating a high-energy proton beam into a rotating helium-cooled tungsten target. These neutrons pass through moderators to reduce their energy to an appropriate range (< 5 meV for cold neutrons); two of which will use liquid hydrogen at 17 K as the moderating and cooling medium. There are several technical challenges to overcome in the design of a robust system that will operate under such conditions, not least the 20 kW of deposited heat. These challenges and the associated design solutions will be detailed in this paper., Published by Inst., Melville, NY

Physics procedia 67, 147 - 152 (2015). doi:10.1016/j.phpro.2015.06.026, The European Spallation Sourcein Lund, Sweden, will be a 5 MW beam power neutron spallation research center. As subsystem of the target station the moderators play a vital role by slowing down high energy neutrons set free during the spallation process. To provide maximum neutron flux intensities with high availability for scattering experiments a conceptual liquid hydrogen moderator cooling circulation design proposal was developed. Supercritical hydrogen at 17 K will be utilized to absorb energy of the incoming neutrons in two parallel moderator vessels. A helium refrigerator provides the necessary cooling capacity by implementing an additional helium expansion turbine downstream the refrigerator coldbox. Strategies for the mitigation of pressure fluctuations due to beam trips are being presented. Solutions in form of electrical heaters and an accumulator or an expansion vessel are discussed. Different supercritical hydrogen circulator implementation scenarios are being matched to indicate the most reliable setup. For an efficient moderation process parahydrogen concentrations higher than 99% have to be guaranteed at the moderator inlet. Due to potential conversion of parahydrogen to orthohydrogen via irradiation processes the implementation of an ortho-parahydrogen catalyst bed is being evaluated. Methods for a continuous measurement of the apparent parahydrogen concentration at the moderator in- and outlet will be introduced. The arrangement and interaction of the components will be detailed in the paper., Published by Elsevier, Amsterdam [u.a.]