The Spallation Neutron Source: A Powerful Tool for Materials Research

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The Spallation Neutron SourceA Powerful Tool
for Materials Research
PAC2001

• T. E. Mason
• Associate Laboratory Director for the SNS

June 18, 2001
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Structure Determines Properties

• 3 forms of Carbon - very different materials

Graphite
Diamond
Buckyballs
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Knowledge of structure and dynamics leads to new
materials

• Superconductors or organic ferromagnets

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Scientific justification for SNS

• Neutrons provide unique insight into materials at
  the atomic level
• see light atoms in biomaterials and polymers
• study magnetic properties and atomic motion
• measure stress in engineering components
• Neutron scattering was developed in the US but we
  now have a serious shortage of facilities and
  they are not best in the world
• State-of-the-art neutron source has been an
  urgent priority for 15 years
• The SNS will be world leading and help restore US
  leadership

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Neutrons and Neutron Sources

• The neutron was discovered in 1932 by Chadwick
• Coherent neutron diffraction (Bragg scattering by
  crystal lattice planes) was first demonstrated in
  1936 by Mitchel Powers and Halban Preiswerk
  as an exercise in wave mechanics
• The possibility of using the scattering of
  neutrons as a probe of materials developed with
  the availability of copious quantities of slow
  neutrons from reactors after 1945. Fermi's group
  used Bragg scattering to measure nuclear
  cross-sections

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Neutrons and Neutron Sources

• A reactor moderates the neutrons produced in the
  fission chain reaction resulting in a Maxwellian
  energy distribution peaked at T (300K).

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Neutrons and Neutron Sources

• The application of slow neutron scattering to the
  study of condensed matter had its birth in the
  work of Wollan and Shull (1948) on neutron powder
  diffraction
• The neutron is a weakly interacting,
  non-perturbing probe with simple, well-understood
  coupling to atoms and spins
• The scattering experiment tells you about the
  sample not the probe

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Neutrons and Neutron Sources

• You can easily work in extreme sample
  environments H,T,P,...) e.g.4He cryostat (Shull
  Wollan) and penetrate into dense samples
• The magnetic and nuclear cross-sections are
  comparable, nuclear cross-sections are similar
  across the periodic table
• Sensitivity to a wide a range of properties, both
  magnetic and structural

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Development of Neutron Science Facilities
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Neutrons Where?

• Fission
• n 235U n n fragments
• moderated by available
• D2O (H2O) to
• E T (Maxwellian)

Sustain chain reaction
200 MeV/n
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Types of Neutron Sources

• Reactor e.g., ILL, France
• 1.5x1015 n/cm2/s2 (recently underwent major
  refurbishment)
• Advantages
• high time averaged flux
• mature technology (source instruments)
• very good for cold neutrons
• Drawbacks
• licensing (cost/politics)
• no time structure

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The Institut Laue-Langevin, Grenoble
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Neutrons Where?

• Spallation
• p heavy nucleus 20 n fragments
• 1GeV e.g. W, Pb, U
• flux
• DR3 Risf 2 x 1014 n/cm2/s
• ILL Grenoble 1.5 x 1015 n/cm2/s
• ISIS average 2 x 1013 n/cm2/s
• 8 x 1015 n/cm2/s

23 MeV/n
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Spallation-Evaporation Production of Neutrons
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Types of Neutron Sources

• Pulsed spallation source e.g., ISIS, LANSCE
• 200 µA, 0.8 GeV, 160 kW
• 2x1013 n/cm2/s2 average flux
• 8x1015 n/cm2/s2 peak flux
• Advantages
• high peak flux
• advantageous time structure for many applications
• accelerator based politics simpler than
  reactors
• technology rapidly evolving
• Disadvantages
• low time averaged flux
• not all application exploit time structure
• rapidly evolving technology

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ISIS Instruments
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The Spallation Neutron Source

• The SNS will begin operation in 2006
• At 2 MW it will be 12x ISIS, the worlds leading
  pulsed spallation source
• The peak thermal neutron flux will be 50-100x
  ILL
• SNS will be the worlds leading facility for
  neutron scattering
• It will be a short drive from HFIR, a reactor
  source with a flux comparable to the ILL

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Spallation Neutron Source

• Worlds largest civilian science project, 1.4
  Billion TPC
• Will attract 1000-2000 users annually
• University vs. industry users dominate
  (four-to-one)

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Project Status

• The FY 2002 request was 291M
• The project now enjoys solid congressional
  support
• Overall project design is 56 complete
• Overall the project is 21.8 complete (through
  March 01) and within budget and schedule
  constraints
• 1.4B and June 2006 completion
• Initial safety documentation is now in place both
  for accelerator and instruments (PSAD) and target
  (PSAR)
• There is good progress on all of the technical
  components front end, superconducting linac,
  ring, target, instruments
• We have excellent ESH performance

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Construction Progress

• Completed two major access roads

• Excavated over 1.4 million cubic yards during
  site preparation
• Completed retention pond
• Completed Linac tunnel excavation
• Front End and Linac Tunnel concrete installation
  under way!

• Completed installation of three temporary
  electrical distribution centers
• Completed Target Building deep foundation
  installation

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Inner plug assembly optimized for performance
Supercritical H2 Moderator decoupled poisoned
Supercritical H2 Moderator coupled
Beryllium Reflector
Lead Reflector
Proton Beam
Ambient Moderator decoupled poisoned
Supercritical H2 Moderator coupled
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Instrument Systems Summary

• Build best-in-class neutron scattering
  instruments to deliver maximum benefit from SNS
  performance characteristics
• Develop shared designs for common components to
  be used by these instruments and future
  instruments
• Carry out RD to drive the design of innovative
  instruments for the project and beyond
• Instruments are being selected in consultation
  with the user community, Instrument Oversight
  Committee (now EFAC)

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SNS will be a USER facility

• User input into the SNS instrument suite
• Instrument Oversight Committee Workshops
• Support (technical, scientific, logistical) for
  users carrying out experiments
• Peer reviewed proposal system
• 1000-2000 users per year from academia,
  government, and industry
• Flexible instrument strategy that supports both
  general user access and dedicated access for
  expert instrument teams that contribute to
  construction and operation of instruments

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Current Instrument Concepts

• Nine instruments have been approved. (boldface
  funded)
• High-resolution backscattering spectrometer
• Magnetism reflectometer
• Liquids reflectometer
• Engineering materials diffractometer
• Extended Q-range small-angle diffractometer
• 6m chopper spectrometer
• Third generation powder diffractometer
• Inelastic spectrometer with 10-100 microvolt
  resolution
• Disordered materials diffractometer
• High pressure diffractometer
• Concepts are being developed for additional
  instruments.
• 2.5 m chopper spectrometer
• High-speed single-crystal diffractometer
• Spin echo
• Fundamental neutron physics

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Instruments in Instrument Hall
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Melittin in Alkanethiol/Phospholipid Hybrid
Bilayer Membranes - NIST
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Melittin in Alkanethiol/Phospholipid Hybrid
Bilayer Membranes - NIST
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Reflectometry

• In addition to providing a unique probe for
  magnetic surfaces and multi-layers polarized
  neutrons permit direct inversion to obtain the
  scattering length density profile - no phase
  problem
• a magnetic reference layer buried in the
  substrate can have magnetization wrt neutron
  polarization varied
• for a weak absorbtion probe (valid for the
  neutron) three known references lead to unique
  solution
• drawback is the price paid in sensitivity for
  polarized beam
• Off-specular reflection for in-plane structure

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Reflectometers

• 2 reflectometers sharing a single beamport
• Requires new multi-channel shutters in the target
  station
• Allows for both vertical sample (magnetism) and
  horizontal sample (liquids) studies

• Novel beam bender optics allows multiplexing and
  reduces background
• Reflectivities lt10-9, 10-50 times faster than any
  existing instrument

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Both Reflectometers w/o Shielding
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VULCAN Is a Compound Instrument Designed to
Tackle Engineering Problems

• Rapid volumetric (3D) mapping with a sampling
  volume of 1 mm3 and a measurement time of minutes
• Very high spatial resolution (0.1 mm) in one
  direction with a measurement time of minutes
• 20 well defined reflections for in-situ loading
  studies
• Ability to study kinetic behaviors in sub second
• Simultaneous SANS measurements

• Ancillary equipment such as furnace and load
  frame will be an integrated part of the
  instrument
• 30x SMARTS at Los Alamos

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cAMP-Dependent Protein Kinase (PKA) Combining
Neutrons with X-rays

• PKA catalyzes a variety of cellular activities,
  ranging from gene induction to color change in
  pigment cells.
• PKA serves as the prototype for a class of
  enzymes which catalyzes protein phosphorylation,
  the major mechanism of cellular regulation.
• The combination of neutron studies and x-ray
  structures of PKA subunits has provided insights
  into the quaternary structure of PKA, which is
  key to the understanding of PKA function.

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SNS SANS

• Extended Q-Range 0.001-12 Å-1
• Moderate resolution
• Performance 3-5 x D22 (ILL) HFIR, 30-100 x
  ISIS

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Q-Coverage
Huey Huang Rice University
3rd Frame
1st Frame
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Powder Diffractometer
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Simulated Diffraction Experiment
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High Pressure Diffractometer
Detectors

• Instrument design dominated by high pressure cell
• Novel high pressure neutron scattering cell
  design based on the megabar piston cylinder cell,
  very stable along thrust axis
• Unique cell design provides large detector
  coverage

Incident beam
Cell designed by Carnegie Institution of
Washington, Geophysical Laboratory.
Sample
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High Pressure Diffractometer Parameters and
Performance

• Atomic structure at pressures up to 100 Gpa
• Moderator decoupled supercritical H2
• Source-sample distance 15 m
• Sample-detector distance 37 cm
• Angular coverage 38-142?, 98-150? horizontal
• 34? vertical
• 5 times the highest pressure of current neutron
  diffractometers
• 200 times the intensity of current high pressure
  neutron diffractometers

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Time-of-Flight Inelastic Instruments

• Two basic types direct geometry fixed Ei
  (e.g. HET chopper)
• Indirect geometry fixed Ef (e.g. IRIS
  backscattering)

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Q-w space accessible with proposed spectrometers
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High Resolution Backscattering Spectrometer

• Crystal analyzer (Si) with 84 m incident flight
  path
• Achieves 2.2 meV resolution at the elastic
  position with
• 250 meV bandwidth
• Can operate up to 18 meV energy transfer with 10
  meV resolution
• Unprecedented capabilities

• Performance gains over comparable reactor
  backscattering instruments gt100 (depending on
  bandwidth needed)
• High-Q option (with Si 311) 500x IN13 and 18x
  IRIS (with 3 times Q range and better resolution!)

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Fermi Chopper Spectrometers
2.5-m chopper spectrometer
6-m chopper spectrometer
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10-100 meV Multi-Chopper Spectrometer
Detector locus
Sample
Guide
Counter-rotating dual-disk high-speed choppers
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Multi-Chopper Spectrometer Parameters and
Performance

• Atomic-scale dynamics in the 0-20 meV energy
  range
• Moderator coupled supercritical H2
• Source-sample distance 42 m
• Sample-detector distance 5 m
• Angular coverage ?30? horizontal
• ?30? vertical
• 1 bank extending to 150?
• Ei (meV) ?E/Ei () flux-on-sample (n/cm2/s)
• 30 3 1?106
• 10 1?107
• 2 3 7?105
• 10 5?106
• Factor of 100 more flux on sample than any other
  disk chopper
• spectrometer at the same resolution and energy
  transfer