Development of a High Intensity Moderator ESS Thomas

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)

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) 2

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 Butterfly Moderator Time average brightness averaged over 42 beamports. Hydrogen moderator of 3 cm height above the target Development International Collaboration on Advanced Neutron Sources (ICANS XXIII) 3

The path to ESS upgrade

The path to ESS upgrade

Upgradeability of ESS n-nbar W 9 W 10 HEIMDAL T-REX MAGIC MIRACLES BIFROST st C-SPEC We BEER NMX upgrade t es W Sleipnir LOKIFREIA HR-NSE North Mono-farm 2 ESTIA Mono-farm 1 SKADI South VOR East ANNI ODIN DREAM VESPA GI-SANS ESPRESSO S 5 upgrade S 6 S 7 Primary upgrade path: more instruments 42 beamports with ~6° separation Upgrade areas ~80% beamport use o 60% for short instruments o 100% for long instruments o >1 instrument on some beamports? WA-NSE scale o o S 8 S 9 S 10 o Monochromator instruments? o 35 -40 instruments possible o Lower moderator not yet defined o all beamports can view both moderators o All beamports allow cold and/or thermal spectrum o Freely tunable wavelength resolution o (K. Andersen) adapt resolution to experimental needs Development International Collaboration on Advanced Neutron Sources (ICANS XXIII) 6

Provisions in Target monolith for source upgrade: • Double decker • Provisions in Target monolith for Neutron antineutron (NNbar) oscillation experiment openings source upgrade: • 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) 7

Liquid Deuterium Moderator For the ESS bottom moderator we propose a LD 2 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) 8

Why liquid 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 D 2 moderator (factor 3 -4 more intense) Intensity vs brightness Zanini et al NIM A 925 (2019) 33 -52 Development International Collaboration on Advanced Neutron Sources (ICANS XXIII) 9

High intensity 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) 10

From High Brightness to High Intensity Development International Collaboration on Advanced Neutron Sources (ICANS XXIII) 11

Top moderator Unprecedented brightness available to all beam ports Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

LD 2 Bottom moderator ranges Higher intensity and different wavelength n-nbar W 9 W 10 HEIMDAL T-REX MAGIC MIRACLES BIFROST st C-SPEC We BEER NMX upgrade t es W D 2 WA-NSE Sleipnir LOKIFREIA HR-NSE North Mono-farm 2 ESTIA Mono-farm 1 SKADI South VOR East ANNI ODIN DREAM scale VESPA GI-SANS ESPRESSO UC N S 5 upgrade S 6 S 7 S 8 S 9 S 10 Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

LD 2 Bottom moderator The Liquid deuterium moderator can serve a VCN moderator D 2 V C N UC N Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

Status of technology High intensity cold UCN VCN Status of material technology mature Liquid D 2 (20 K) Mature in beam Challenges in-pile At the beginning Liquid He (~1 K) Clathrates …? Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

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)

VCN moderator thermal (water) cold (hydrogen) very cold (? ? ) (K. Andersen) For increase of VCN there are two possibilities: 1. Enhancement of the cold tail of the LD 2 via quasi-specular reflection from nanodiamonds or other reflectors 2. Development of a dedicated VCN moderator. For this, the research is at an early stage Study of candidate material -theory (O. Zimmer) -Cross section measurements

Beam Extraction 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) 18

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

Other interesting material to study for cold neutron reflection • Mg. H 2 (Rolando Granada et al. ) ENS 2019 • Deuterated clathrate hydrates Oliver Zimmer (Phys. Rev. C 93, 035503) Development International Collaboration on Advanced Neutron Sources (ICANS XXIII) 20

Scattering Kernel and Neutron Transport Properties • • To study the material we propose we need to be able to perform neutronics calculations Neutronic calculations involving thermal and subthermal neutron energies demand the knowledge of reliable cross section data relative to the materials we want to study Molecular Modelling Kernel Software Molecular dynamics code DFT Density Functional Theory code NJOY NCrystal XSEC ACE file Development International Collaboration on Advanced Neutron Sources (ICANS XXIII) MCNP GEANT 4 21

Benchmark with experimental measurements o For some materials there already some data available (nanodiamonds, Mg. H 2) o For other materials there is few information o For other materials the cross section can be sample dependent • Where information is missing we plan to perform experimental measurement Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

From Scattering Kernel to final instrument design Mc. Stas Instrument Optimization MCNP/GEANT 4 With scattering Kernel for: Nanodiamonds Mg. H 2 Clathrate Hydrate ………. Moderator Design Beam Extraction Design ESS future instruments Development International Collaboration on Advanced Neutron Sources (ICANS XXIII)

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) 24

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