Optimization of moderators and beam extraction at the ESS

Ken Holst Andersen *, Mads Bertelsen, Luca Zanini, Esben Bryndt Klinkby, Troels Schonfeldt, Phillip Martin Bentley, Jan Saroun

*Corresponding author for this work

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    Abstract

    A global approach coupling the moderator to the beam extraction system has been applied for the design optimization of the thermal and cold moderators of the European Spallation Source (ESS), which will be the brightest neutron source in the world for condensed-matter studies. The design is based on the recently developed high-brightness low-dimensional moderator concepts. Para-hydrogen is used for the cold neutron source, while thermal neutrons are provided by moderation in water. The overall moderation configuration was chosen in order to satisfy a range of requirements on bispectral extraction, beamport configuration and instrument performance. All instruments are served by a single moderator assembly above the target, arranged in a `butterfly' geometry with a height of 3cm. This was determined to be the optimal height for trade-off between high brightness and efficient guide illumination, by analysis of the performance of 23 instruments, based on the reference suite of the ESS Technical Design Report. The concept of `brilliance transfer' is introduced to quantify the performance of the neutron optical system from the source to the sample. The target monolith incorporates a grid of 42 neutron beamports with an average separation of 6 degrees, allowing a free choice between cold and thermal neutron sources at all instrument positions. With the large number of beamports and the space below the target available for future moderators, ample opportunities are available for future upgrades.
    Original languageEnglish
    JournalJournal of Applied Crystallography
    Volume51
    Issue number2
    Pages (from-to)264-281
    Number of pages18
    ISSN0021-8898
    DOIs
    Publication statusPublished - 2018

    Keywords

    • Water moderators
    • Para-hydrogen moderators
    • Low-dimensional moderators
    • Pancake moderators
    • Butterfly moderators
    • Brilliance transfer
    • Neutron instruments

    Cite this

    Holst Andersen , K., Bertelsen, M., Zanini, L., Klinkby, E. B., Schonfeldt, T., Bentley, P. M., & Saroun, J. (2018). Optimization of moderators and beam extraction at the ESS. Journal of Applied Crystallography, 51(2), 264-281. https://doi.org/10.1107/S1600576718002406