Development of a High-Intensity Moderator at ESS for ICANS XXIII

1. Development of a High Intensity Moderator @ ESS Thomas Miller on behalf of the ESS Bottom Moderator team International Collaboration on Advanced Neutron Sources (ICANS XXIII)

2. Outline • The ESS current moderator • ESS upgrade capability • The ESS future moderator design • Beam Extraction system studies Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

3. The ESS current moderator The design of ESS moderator was based on the novel concept of low-dimensional moderators . It is a single high-brightness moderator system placed on top of the spallation target. All of the first 15 instruments built, plus a test beam line, will view that moderator Time average brightness averaged over 42 beamports. Butterfly Moderator Hydrogen moderator of 3 cm height above the target Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

4. The path to ESS upgrade

5. The path to ESS upgrade

6. Upgradeability of ESS n-nbar upgrade W10 W9 HEIMDAL T-REX MAGIC MIRACLES West BIFROST West C-SPEC BEER NMX WA-NSE Sleipnir LOKI FREIA North HR-NSE Mono-farm 2 ESTIA Mono-farm 1 South East SKADI ODIN ANNI VOR DREAM VESPA GI-SANS ESPRESSO scale S5 upgrade (K. Andersen) S6 S7 S8 S10 S9 • Primary upgrade path: more instruments • 42 beamports with ~6° separation • Upgrade areas • ~80% beamport use • 60% for short instruments • 100% for long instruments • >1 instrument on some beamports? • Monochromator instruments? • 35-40 instruments possible • Lower moderator not yet defined • all beamports can view both moderators • All beamports allow cold and/or thermal spectrum • Freely tunable wavelength resolution • adapt resolution to experimental needs Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

7. Provisions in Target monolith for source upgrade: Provisions in Target monolith for source upgrade: Double decker Neutron antineutron (NNbar) oscillation experiment openings Twister elements below target (currently with a steel plug) Larger space in inner shielding below target wrt to above Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

8. Liquid Deuterium Moderator For the ESS bottom moderator wepropose a LD2 moderator • It has higher intensity than top moderator. • It can serve several beam lines with cold neutrons • It can serve a second moderator or converter • UCN moderator (in beam or in pile) • VCN moderator Reflector Preliminary studies done already in 2014 E. Klinkby et al.,https://arxiv.org/pdf/1401.6003.pdf Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

9. Whyliquid deuterium? To increase the intensity (total number of neutrons), parahydrogen is not viable (3 cm moderator delivers 80% of the max intensity). A better way is to use voluminous D2 moderator (factor 3-4 more intense) Intensity vs brightness Zaniniet al NIM A 925 (2019) 33-52 Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

10. Highintensity neutron source applications • The High intensity moderator will boost applications as • Fundamental Physics (n->n oscillations, E.D.M. measurement) • Imaging • Spin-echo • SANS Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

11. From HighBrightness to HighIntensity Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

12. Top moderatorUnprecedented brightness available to all beam ports Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

13. LD2 Bottom moderator ranges Higher intensity and different wavelength n-nbar upgrade W10 W9 HEIMDAL T-REX MAGIC MIRACLES D2 West BIFROST West C-SPEC BEER NMX WA-NSE Sleipnir LOKI FREIA North HR-NSE Mono-farm 2 ESTIA Mono-farm 1 South East SKADI ODIN ANNI VOR DREAM VESPA GI-SANS ESPRESSO scale UCN S5 upgrade S6 S7 S8 S10 S9 Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

14. LD2 Bottom moderator The Liquid deuterium moderator can serve a VCN moderator D2 VCN UCN Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

15. Status of technology Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

16. UCN converter Technology is UCN converters is known and used Possibilities at ESS: in beam and in pile Both will be studied. Engineering feasibility increasingly difficult if He converter is placed close to the target. We will determine how close we can go (courtesy A. Serebrov) Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

17. VCN moderator thermal (water) cold (hydrogen) very cold (??) For increaseof VCN therearetwopossibilities: Enhancementof the coldtailof the LD2 via quasi-specularreflection from nanodiamonds or otherreflectors Developmentof a dedicated VCN moderator. For this, the research is at an earlystage Studyofcandidate material           -theory (O. Zimmer)           -Cross sectionmeasurements (K. Andersen)

18. BeamExtraction System In addition to the development of the future ESS moderator we plan also to study novel beam extraction techniques In recent years some very promising developments has been done in the field of reflectors. For the reflector we do not only consider the bulky material around the moderator but also thin layer of materials to provide a reflection of the cold neutron that could be used in the beam extraction system Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

19. Nanodiamonds Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

20. Otherinteresting material to study for cold neutron reflection MgH2 (Rolando Granada et al. ) ENS 2019 Deuteratedclathratehydrates Oliver Zimmer (Phys. Rev. C 93, 035503) Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

21. ScatteringKernel and Neutron Transport Properties • To study the material weproposeweneed to be able to performneutronicscalculations • Neutroniccalculationsinvolvingthermal and subthermal neutron energiesdemand the knowledgeofreliable cross section data relative to the materials wewant to study Moleculardynamicscode Molecular Modelling DFT DensityFunctionalTheorycode Kernel Software NCrystal XSEC MCNP ACE file GEANT4 NJOY Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

22. Benchmark with experimental measurements • For some materials therealreadysome data available (nanodiamonds, MgH2) • For other materials there is few information • For other materials the cross sectioncan be sampledependent • Where information is missingwe plan to perform experimental measurement Development International Collaboration on Advanced Neutron Sources (ICANS XXIII) 22

23. From ScatteringKernel to final instrument design McStas Instrument Optimization Moderator Design Beam Extraction Design MCNP/GEANT4 With scattering Kernel for: Nanodiamonds MgH2 Clathrate Hydrate ………. ESS future instruments Development International Collaboration on Advanced Neutron Sources (ICANS XXIII) 23

24. Conclusions • ESS will start the User Program with one moderator of exceptional brightness • For the ESS upgrade we want to develop a high intensity moderator • The new moderator, would boost the performance of applications such as imaging, spin-echo, small-angle scattering and fundamental physics by an order of magnitude or more, compared to the top (high-brightness) moderator. • In addition to that we plan to study a beam extraction system based on new reflectors material • Stay tuned Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

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