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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.

The design of neutron instruments usually is related to the simulations of neutron beams. These simulations are normally decoupled from the neutron source since the nuclear reactions that govern the generation of neutrons in the source are independent of the specific interactions that take place in the neutron beam path. Also, neutron beams are usually transported far away from the source to reduce the background signal in the measurements and the radiation dose of the personnel. When evaluating the neutron beam under different operating conditions, it is useful to have a source that can be re-sampled. KDSource [1,2] is an open-source code that uses the adaptive multivariate Kernel Density Estimation (KDE) method to estimate the source distribution at a given point in the beam trajectory, which seeks to overcome limitations of other variance-reduction techniques. The approach presents a novel methodology to optimize source modelling, which may be especially suited for neutron beam and radiation shielding simulations. The core idea of the methodology is to use some machine learning libraries and algorithms to optimize the bandwidth selection for each source variable. With this strategy, smooth estimates of the variable distributions may be obtained from particle lists at a given point in a simulation that maintains correlations among all the variables. The code implements the proposed methodology in Python, and it consists of a module for KDE model optimization, and another for sampling (i.e. generating new particles using the previously optimized model). This work aims to present the KDSource code with some usage examples to design the neutron imaging instruments for the HBS project. [1] N.S. Schmidt, O.I. Abbate, Z.M. Prieto, J.I. Robledo, J.I. Márquez Damián, A.A. Márquez, J. Dawidowski, 2022. KDSource, a tool for the generation of Monte Carlo particle sources using kernel density estimation. Ann. Nucl. Energy 177. URL: https://doi.org/10.1016/j.anucene.2022.109309 [2] O.I. Abbate, N.S. Schmidt, Z.M. Prieto, J.I. Robledo, J.I. Márquez Damián, A.A. Márquez, J. Dawidowski, 2021. KDSource, a tool for the generation of Monte Carlo particle sources using kernel density estimation. GitHub repository. URL: https://github.com/KDSource/KDSource

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.

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

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