Baseline Review

The Path of ARCS from Science

to a ProjectBrent 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 ln.

F = E – TS favors different structures of materials.

(Parallel thermodynamics for magnetic scattering.)

Phonon Scattering

Ei < 70 meV, light elements higher

d/d 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 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

T0

E0

Pit Area

Sample

Beamstop

Detectors

SNS EFAC selection of two:

• high flux

• high resolution

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

ARCS2% resolution140o at 3 m

CNCS (Ei<50 meV)

2% resolution140o at 3 m

SNACS1% resolution45o at 5.5 m

The Present Concept for ARCS

Angle-Range Chopper SpectrometerA High-Resolution Direct-Geometry Chopper SpectrometerA 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 RoadmapdataI1(, )t2(I , )t

(In , )t

rebindeconvcalibbkgd

( , )S Q Erecognition .multiple excit .multiple scatt

+ – /x

excitationsdispersionsDOS

fullsimulationmodelcomparecomparetoolstoolsphysicsphysicalscattering

:PRL:PRL:PRLNexus file format

converter

ISAWGenie

/Homer Iliad ( )Lamp IDL ( )Treat NIST Signal

Processing

MSLICEISAWMscatMuflcorCaltechMaxent

TobyfitChop- B v K codesUnisoftNCA

84XTAL

McStasVitessIdeas

GraphicsWindowMSLICEISAWIDLMatlabOpenGL

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

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

Primary Flight Path<kf|H|ki>Secondary Flight PathDetectorSourceSampleSimulationComparisonDataPhysicsModulesSample

ModulesConvergence

Modules

ARCS -- The Project -- Software200120022003200420052006Project Year01234520071. Initiationhardware, data stds., architecture, roadmap

2. S(Q,E)calibrations, DOS, χ”, dispersions

3. Visualization3- D development

, Matlab IDL

4. Modeling ( , )of S Q E

5. Monte Carlo MacStas with

sample dynamics

6. ConfigurationControl

testing and builds

7. Release Management

, QA platformissues

take inventory take inventory take inventory take inventory/Pythonize Integrate/Pythonize Integrate/ / /Experiment Theory Build Pythonize 14Mar / / /Experiment Theory Bulid PythonizeTasks

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”

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)

Fact: ARCS will be the fundamental condensed matter science instrument at the $ 1,411,000,000 SNS.

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 scheduleMemorandum 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