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Neutron beam extraction from small moderators: secondary source approach

Neutron beam extraction from small moderators: secondary source approach. Thomas Huegle Alexandru Stoica October 2019. Definitions and Goal. Large moderator case. Shape developed by Ducu Stoica 3 conditions: Direct line of sight maintained Limits guide entrance size

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Neutron beam extraction from small moderators: secondary source approach

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  1. Neutron beam extraction from small moderators: secondary source approach Thomas Huegle Alexandru Stoica October 2019

  2. Definitions and Goal

  3. Large moderator case • Shape developed by Ducu Stoica • 3 conditions: • Direct line of sight maintained • Limits guide entrance size • Only one reflection • Limits length and slope • No reflection “out of moderator” • Limits slope at guide exit Every trajectory coming from the sample has to end on the moderator surface! MATH* * Frost, M. J.; Stoica, A. D.; Huegle, T. A First-Principles Approach to the Optimization of Neutron-Focusing Guide Design and Development. Journal of Neutron Research2019, 20 (4), 131–135.

  4. Unresolved Questions: • How to optimize two guide pieces to each other? • How to get out of direct line of view?

  5. High brightness source • n/s/Å/cm2/sr • Small moderators • Project image of moderator • Ellipse: aberrations magnification demagnification

  6. Two Symmetric Ellipses with secondary source Secondary Source

  7. Divergence map at sample position Moderator First guide Second guide Sample

  8. Montel Optics Secondary Source http://www.x-ray-optics.de/index.php/en/types-of-optics/reflecting-optics/curved-mirrors

  9. What happens when we change the ellipse size?

  10. Divergence vs. position: unoptimized case At secondary source: At sample position:

  11. How to optimize to each other (secondary source) • Remember 3 conditions: no holes in phase space! • Easy to imagine for rectangular moderator • Hard to imagine for secondary source produced by 2-sided ellipse • Back projection Every trajectory coming from the sample has to end on the moderator surface!

  12. What went wrong? At Secondary Source: Match phase space from moderator to that back-projected from sample!

  13. How to do better?

  14. Match Acceptance • Multiple second guide pieces to choose from? • Extend first guide to accommodate all second guide options

  15. Brilliance transfer

  16. Slits at secondary source

  17. Summary At Secondary Source: Match phase space from moderator to that back-projected from sample! Special Thanks to Chris Layton (CADES) This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under contract number DE-AC05-00OR22725. This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. This research used resources of the Compute and Data Environment for Science (CADES) at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725.

  18. Case for 2 equal ellipses

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