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With very few large-scale facilities left to serve a leading community of about 5000 European neutron usersin the 2030s, the European neutron ecosystem will become extremely vulnerable and capacity-limited. Neutronresearch in Europe risks losing its strength and diversity if limited access to neutron beam time makes itextremely difficult to maintain a sustainable research program based on the use of neutrons.High Current Accelerator driven Neutron Sources (HiCANS) are a completely new type of neutron researchfacility based on an innovative concept. They have the potential to rejuvenate the European neutron ecosystemand provide complementary capabilities. The High Brilliance Neutron Source (HBS) project is a highlyambitious HiCANS project characterized by cost efficiency, sustainability, reliability, resilience, easy accessand flexibility.We present the concept of the HBS, discuss the physical and technical solutions for challenging componentssuch as the high-power target, report on simulations and experimental verifications, and prototyping for allmajor components of the facility. The HBS features a complete set of instruments for diffraction, large-scalestructural research, inelastic scattering, and high-resolution spectroscopy, imaging, and neutron analyticswith highly competitive instrument performance. The Technical Design Report (TDR) provides a blueprintfor construction of the facility.This work is part of the collaboration within ELENA and LENS on the development of HiCANS.

In recent years, the interest in low energy compact accelerator-driven neutron sources (CANS)has increased worldwide. The focus of this interest is shifting more and more from smalluniversity based CANS to powerful high flux CANS that have the potential to replace currentreactor based neutron sources and possible alternatives to spallation sources.Within the framework of the Jülich High Brilliance Neutron Source (HBS) project, a high fluxaccelerator based neutron source is developed. One of the key components as well as themain power-limiting factor is the target that releases neutrons from the impinging protonsvia nuclear reactions. Since the neutron yield of nuclear reactions is quite small, this iscompensated with a high proton current. However, the high proton current leads to a strongheat release inside the target. At the same time the target has to be very compact to allowthe subsequent extraction of a neutron beam with a high brilliance. Overall, this leads tounique requirements of the HBS target given by a 70 MeV pulsed proton beam with a peakcurrent of 100 mA and an average thermal power release of 100 kW inside the target with asurface area of 100 cm².A solid tantalum target prototype with an innovative micro channel water cooling structurewas developed, manufactured, and successfully tested to match these requirements. Knownproblems from low energy targets like blistering, limited heat dissipation and highthermomechanical stresses have been consequently minimized during the development.Feedback from the production process helped to eliminate known weak points of theprototype. The coolant erosion resistance of the micro channel structure was demonstratedin a six-week endurance experiment, to exclude possible concerns on this. Furthermore, thetarget was successfully high heat flux tested at ~1 kW/cm² in the electron beam facilityJUDITH 2 and with these measurements the design simulations of the target could bevalidated. The specifics of the HBS target concept as well as the results of the experimentalheat load and erosion tests will be presented.

Compact Accelerator-driven Neutron Sources (CANS) have the advantage (compared to researchreactors or spallation sources) that the primary neutrons are emitted from a volume well below 1 dm3.The thermal moderator is used to change the energy of the primary neutrons (typically in the MeVrange) down to the 100 meV range, where they are useful for the structural investigation of matter.This moderation process takes place by multiple scattering events with the nuclei of the moderatormaterial(s). To be able to extract neutron beams efficiently from the thermal moderator, it isimportant not to dilute the primary neutron cloud too much, but to keep it confined and dense forthe time of the neutron pulse length desired.The different materials useful for building a moderator-reflector assembly around a target of a CANSdiffer in their absorption probability, scattering power, and energy transfer during a single neutronscattering event. The scattering leads to energy loss and confinement (by a randomized flight directionof the neutron after the scattering), while absorption and diffusion out of the moderator -reflectorregion are the main mechanisms of intensity decay. Some typical materials are e.g. light water orpolyethylene as hydrogen rich materials that lead to fast energy transfer (complete thermalizationwithin 7 μs) and a good confinement of the thermal neutron cloud (about 8 cm FWHM), but thethermal neutrons decay with a time constant below 200 μs due to the nuclear absorption by thehydrogen nuclei. Beryllium or lead show a much weaker scattering probability and a lower energytransfer, which lead to slower moderation, a larger size of the thermal neutron cloud, but a longerlifetime due to an absorption probability that is several orders of magnitude lower.We try to optimize the geometry and the combination of materials in a way to be able to provide theextraction of several neutron beams from a single moderator-reflector assembly with a suitable pulsetime structure either for thermal neutron instruments or for feeding cold neutron sources insertedinto the thermal moderator assembly.

The Jülich Centre for Neutron Science is working on the project to develop, design and demonstrate anaccelerator driven high-brilliance neutron source (HBS) as an efficient and cost-effective alternative tocurrent low- and medium-flux reactor and spallation sources. The HBS comprises a high current protonacceleratorwith an energy of 70 MeV and a beam current of 100 mA, a compact neutron target of 100 kWpower, sophisticated cold and thermal moderator systems and an optimized neutron transport system toprovide thermal and cold neutrons with high brilliance for a full suite of epithermal, thermal and coldinstruments.The project offers construction of a scalable neutron source fora user facility with open access and serviceaccording to the various and changing demand of its communities. Embedded within an internationalcollaboration with partners from Germany, Europe and Japan the Jülich HBS project offers best flexiblesolutions to the scientific and industrial users. The overall conceptual design of HBS was published in arecent report.We will present the current status of the project, progress and next steps regarding accelerator, target,moderators and beam delivery development, milestones and the vision for the realization of such a facility.

With the decommissioning of research reactors in Europe and elsewhere in recent years, theavailable capacity on neutrons for science is declining and access is becoming crucial for neutronusers. Responding to this development and to offer an alternative way on new neutron sources,the High Brilliance Neutron Source (HBS) project was initiated at the Jülich Centre for NeutronScience (JCNS) at the Forschungszentrum Jülich. It aims at developing a high-current acceleratordrivenneutron source (Hi-CANS) to deliver high-brilliant neutron beams to a variety of neutronscattering instruments. Within the framework of this project, a compact tantalum neutronproductiontarget with a sophisticated internal microchannel cooling was developed for a 70 MeVproton beam with a peak current of 100 mA and an average power of 100 kW for a target areaof 100 cm². The high-power density requires an optimization of the microchannel coolingstructure to reduce temperatures and to minimize thermo-mechanical stresses, whereas thehigh-current requires a design minimizing proton accumulation within the tantalum target toavoid relevant blistering problems. In order to get such an optimal design, the microchannelgeometry was gradually adapted using the particle transport code FLUKA and thermo-mechanicalsimulations with ANSYS. The details of these investigations and the resulting microchannel targetdesign will be presented.

The shutdown of several national reactor driven neutron sources has stimulated intense research and development activities for successor facilities[1]. A promising technology is the neutron production by low energy nuclear reactions, that can be driven by accelerators operating in the particle energy range between 3 and 100 MeV. While the neutron yield of theses reactions is much lower than the neutron yield of the spallation reaction, the lower particle energy enables a very close coupling of the thermal and cryogenic moderators to the target and therefore small volume moderators with a high density of slow neutrons. On the other hand, the comparably low particle energies facilitate the shielding issue significantly and allow therefore neutron optical components in a distance as close as 50 cm from the thermal or cold moderator surfaces allowing the extraction of a reasonably divergent beam from the source, which can be efficiently transported to the sample by modern neutron optics. Therefore instruments, which require a large phase space, can benefit strongly from the characteristics of a low energy accelerator driven neutron facility (LENF). Among them are typically spectrometers of both direct and indirect geometry, which require typically relaxed spatial and angular resolution and a good energy resolution. Here we present source parameters that have been determined for different spectrometers employing thermal and cold neutrons.

The High Brilliance Neutron Source (HBS) project was initiated at the Jülich Centre for Neutron Science of the Forschungszentrum Jülich (JCNS). It aims to develop a medium neutron source facility based on a linear accelerator, scalable up to 70 MeV proton energy and optimized to deliver high brilliance neutron beams to a variety of neutron instruments. In the framework of this project a compact micro channel target was proposed for the powerful high-flux and compact, accelerator-driven neutron sources (CANS). Based on earlier simulations concerning fluid dynamics and structural mechanics, a preliminary design was developed. Due to the required compactness, heat dissipation and mechanical stability are the factors limiting the total neutron yield of the target. In order to find a compromise solution between high neutron yield and mechanical stability, the energy desposition as well as neutron and proton spectrum in different geometric parameters of the micro-channel target were performed with the Monte Carlo simulation code FLUKA. The details of the simulation and optimization will be presented at the workshop.

Jülich : Forschungszentrum Jülich GmbH, Zentralbibliothek, Schriften des Forschungszentrums Jülich. Reihe Allgemeines 8, 197 Seiten : Illustrationen, Diagramme, Karten (2020)., Published by Forschungszentrum Jülich GmbH, Zentralbibliothek, Jülich

New journal of physics 22(9), 093001 (2020). doi:10.1088/1367-2630/abaa02, Published by IOP, [London]

Neutron news 31(2-4), 37 - 43 (2020). doi:10.1080/10448632.2020.1819132, Published by Taylor and Francis, London [u.a.]

Materials Research Express 7(11), 116404 - (2020). doi:10.1088/2053-1591/abc58b, Published by IOP Publ., Bristol

Strontium cobaltite (SrCoO2.5+δ, SCO) is a fascinating material because of its topotactic structural phase transition caused by a change in oxygen stoichiometry. In the brownmillerite phase (δ = 0) it is an insulating antiferromagnet whereas in the perovskite phase (δ = 0.5) it is a conducting ferromagnet. In contrast, the impact of the varying Co/Sr stoichiometry on the structure has not yet been studied in SCO thin films. Using molecular beam epitaxy we have fabricated SCO thin films of varying Co/Sr stoichiometry. Films with Co excess exhibit a brownmillerite crystal structure with CoO precipitates within the thin film and on the surface. Co deficient films are amorphous. Only for 1:1 stoichiometry a pure brownmillerite structure is present. We find a clear dependence of the Reflection High Energy Electron Diffraction (RHEED) pattern of these thin films on the stoichiometry. Interestingly, RHEED is very sensitive to a Co excess of less than 12% while x-ray diffraction fails to reveal that difference. Hence, using RHEED, the stoichiometry of SCO can be evaluated and tuned in-situ to a high degree of precision, which allows for a quick adjustment of the growth parameters during a sample series.

RBS raw date for publication "Tuning the Co/Sr stoichiometry of SrCoO2.5 thin films by RHEED assisted MBEgrowth" Simulation results using SIMNRA included as well