Baseline Review The Path of ARCS from Science to a Project

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Baseline ReviewThe Path of ARCS from Science
to a Project

• Brent Fultz
• California Institute of Technology

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Magnetic Excitations

• Energy of the excitations can be large, often
  beyond
• the spectrum from reactor sources.
• d- and f-electron form factors are large in r,
  small in k
• For small Q and high Ei, forward detector
  coverage
• must be good.

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Examples of Magnetic Excitations

• KCuF3 a 1D
• Heisenberg antiferromagnet
• quantized excitations in
• spin chain
• calculated by field theory
• sharp dispersive modes
• continuum from
• free spinons (not FD or BE)

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Examples of Magnetic Excitations
KCuF3 is a linear crystal, aligned along qi It is
a special case, but 2D crystals can also be
accommodated 3D crystals require goniometer
manipulation
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Phonon Scattering
Thermodynamics of materials T 0 all internal
coordinates in ground state. T gt 0 creates
excitations. Degeneracy of excitations gives
entropy S k lnW. F E TS favors different
structures of materials. (Parallel
thermodynamics for magnetic scattering.)
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Phonon Scattering
Ei lt 70 meV, light elements higher ds/dW Q2,
prefer higher Q (until multiphonon
problems) Q-dependence needed for data analysis
from coherent scattering and separation
of magnetic scattering
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Everybody wants More Flux!

• No inelastic neutron scattering experiment has
  ever
• suffered from excessive flux
• SNS source and p steradian detector coverage
• will give ARCS new capabilities in
  practice
• 1. Parametric studies
• Present -- compare A vs. B. Future
  -- A(T,H) vs. B(T,H)
• 2. Single crystals
• 3. Small quantities of new materials
• 4. Sample environments

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History
1. HELIOS (Mason, Broholm, Fultz)
Abernathy
too 2. VERTEX (McQueeney, Fultz) 3. SNS EFAC
selection of two (Abernathy) 4. ARCS
proposal, June 2001 (held the U.S. community
together)
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History

• SNS EFAC
• selection of two
• high flux
• high resolution

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Proposed ARCS
Reviewer Comments 1. Do not use 2 flightpaths
(not universal opinion) 2. Software is a big
job
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Bifurcation of ARCS

• Full instrument had no contingency funds
• Canadian CFI program prompted interest in a
• second high-energy chopper instrument
• International class facility should have a
  general
• purpose and a magnetism instrument

Presently
CNCS (Eilt50 meV) 2 resolution 140o at 3 m
SNACS 1 resolution 45o at 5.5 m
ARCS 2 resolution 140o at 3 m
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The Present Concept for ARCS
Angle-Range Chopper Spectrometer A
High-Resolution Direct-Geometry Chopper
Spectrometer A Medium-Resolution Chopper
Spectrometer
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The Present Concept for ARCS
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ARCS -- The Project -- Hardware
d2A/dt2 lt 0
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ARCS -- The Project -- Budget
d2/dt2 gt 0
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ARCS -- Software Roadmap
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Road 1 S(Q,E) from TOF Data

• Bare minimum for users to take home
• General model independent
• Non-trivial for single crystals, especially when
  real-time decisions on 3D sample orientation are
  required
• Must accommodate different visualization needs of
  different users, and packages such as Matlab and
  IDL
• Outside the scope data mining e.g.,
  recognition of dispersions

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Road 2 Fits and Inversions of S(Q,E)

• Analytical results from the theory of thermal
  neutron scattering by condensed matter
• Monte-Carlo inversions of measured data to
  obtain, for example, force constants or exchange
  energies

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Road 3 Full Experiment Simulations
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ARCS -- The Project -- Software
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ARCS -- The Project -- Scope
ARCS will be finished and working at the end of
the project.

• No missing detectors
• Software for data acquisition and analysis
• including a menu of working Python scripts
• Some sample environment

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ARCS -- The Project -- Some Stakeholder Issues
Stakeholder Expectations ARCS will be
finished and working on time and under
budget.

• DOE BES reporting and reviewing
  requirements
• U.S. user community / ARCS IDT
• communications, engage in software, sample
  environment
• SNS
• interface, MOU with Caltech
• ARCS staff
• hiring postdoctoral fellows, designers,
  funds between Caltech and ANL
• Caltech and ANL
• surprisingly quiet

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ARCS -- The Project -- Quality Policy
Fact ARCS will be the fundamental
condensed matter science instrument at the
1,411,000,000 SNS.
Policy ARCS must be a full system
solution reliable, maintainable, and
scientifically productive

• best engineering practice
• few risks
• emphasize quality over quantity
• (e.g., completed detector coverage even if
• some sacrifice in resolution)

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ARCS -- The Project -- Risks
Technical operation of detectors in vacuum
(test facility underway) sample environment for
single crystals (user community still
undecided)
Cost and Schedule Infrastructure for
installation (we might follow other
instruments, but not by much) Budget authority
and float in schedule Memorandum of
Understanding (awaiting action by SNS, 3He
reduces detector contingency) Taxes Tennessee
state, Caltech overhead (switch title?)
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ARCS -- The Project -- Key People and Institutions
Brent Fultz -- Caltech (project leader,
coordinator, aligner of personnel) Doug
Abernathy -- Argonne, Caltech (Oak Ridge too)
(hardware project manager, Visiting Associate
in Materials Science) Michael Aivazis --
Caltech (software project manager) Hardware
Engineering -- Argonne Hardware Construction --
Oak Ridge Software -- Caltech Science --
centered at Caltech
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ARCS -- The Project -- Funding
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ARCS -- The Project -- Baseline Review
1. Check the instrument concept High
intensity Decent resolution 2
Completed hardware Significant software 2.
Examine the details of the project plan Some
missing, but can you see the picture clearly
enough to tell if the cost and schedule are
realistic? 3. Emphasis Are we missing
something?
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ARCS -- The Project -- Management
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ARCS -- The Project -- Software
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ARCS -- The Project -- Management
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Future Directions -- Developments in Concepts

• 1. Software Enabled
• coherent scattering from polycrystals
• disordered solids
• 2. Hardware and Software
• coherent scattering from 3D single crystals