Download Instrument Systems - Timing Review

Baseline Review
The Path of ARCS
from Science
to a Project
Brent Fultz
California Institute of Technology
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.
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)
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
Phonon Scattering
Thermodynamics of materials
T = 0 all internal coordinates in ground state.
T > 0 creates excitations.
Degeneracy of excitations gives entropy S = k lnW.
F = E – TS favors different structures of materials.
(Parallel thermodynamics for magnetic scattering.)
Phonon Scattering
Ei < 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
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
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)
History
Pit Area
SNS EFAC
selection of two:
• high flux
Beamstop
Sample
• high resolution
E0
Detectors
T0
Proposed ARCS
Reviewer Comments:
1. Do not use 2 flightpaths
(not universal opinion)
2. Software is a big job
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
ARCS
2% resolution
140o at 3 m
SNACS
1% resolution
45o at 5.5 m
CNCS (Ei<50 meV)
2% resolution
140o at 3 m
The Present Concept for ARCS
Angle-Range Chopper Spectrometer
A High-Resolution Direct-Geometry Chopper Spectrometer
A Medium-Resolution Chopper Spectrometer
The Present Concept for ARCS
ARCS -- The Project -- Hardware
d2A/dt2 < 0
ARCS -- The Project -- Budget
d2$/dt2 > 0
ARCS -- Software Roadmap
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 realtime 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
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
Road 3 – Full Experiment Simulations
ARCS -- The Project -- Software
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
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
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)
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?)
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
ARCS -- The Project -- Funding
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?
ARCS -- The Project -- Management
ARCS -- The Project -- Software
ARCS -- The Project -- Management
Future Directions -- Developments in Concepts
1. Software Enabled
• coherent scattering from polycrystals
• disordered solids
2. Hardware and Software
• coherent scattering from 3D single crystals