Conceptual design and performance of high throughput cold spectrometer :

MACS

Why MACS Layout and key elements Performance Data collection Scientific program Budget and schedule

Conclusion

Collin BroholmJohns Hopkins University and NIST Center for Neutron Research

NSF/NIST 10/19/00

MACS development team

Overall instrument designPaul Brand NISTChristoph Brocker NISTCollin Broholm JHU Jeff Lynn NISTMike Rowe NISTJack Rush NISTYiming Qiu JHU

Focusing MonochromatorSteve Conard JHUJoe Orndorff JHUTim Reeves JHUGregg Scharfstein JHU Stephen Smee UMDShielding CalculationsCharles M. Eisenhauer

NSF/NIST 10/19/00

Why cold neutrons and double focusing

• Q and E resolved spectroscopy requires 11.01.0 aQJE

Lattice Compound J (meV) a (Å)3D Cubic S=5/2 La0.7Pb0.3MnO3 8.8 3.92D Square S=1/2 La2CuO4 132 5.42D Kagomé S=3/2 KCr3(OH)6(SO4)2 1.2 3.72D Kagomé S=3/2 SrCr9Ga3O19 10 2.91D S=1/2 chain Cu(C6D5COO)2

.3D2O 1.5 3.21D S=1/2 chain KCuF3 35 3.91D S=1 chain NENP 4.1 5.21D S=1 chain AgVP2S6 58 2.9

• Energy scale J varies more than length scale a

• To probe a range of materials must vary keeping • To probe hard matter with low energy scales

• Reduce Ei. Cold source provides the flux• Increase angular divergence before and after sample

meV 10meV 10 2 E 105.0 AQ

NSF/NIST 10/19/00

Kinematic limits for neutron scattering

Efix and 2 range determine accessible Q-E spaceEfix and 2 range determine accessible Q-E space

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Comparing TOF to TAS

• Larger detector solid angle

• E-scan with “no” moving parts

• Can use pulsed spallation source peak flux

• Larger detector solid angle

• E-scan with “no” moving parts

• Can use pulsed spallation source peak flux

• Can focus beams with Bragg optics

• Can select range of energy transfer

• Can use reactor CW flux

• Can focus beams with Bragg optics

• Can select range of energy transfer

• Can use reactor CW flux

TAS like

TOF like

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NCNR Liquid Hydrogen cold source

MACS Beam

New cold source to be installed in 2001 will double flux

K 45

/n/cm 108.4 213

effT

s

Overview of MACS

Design by C. Brocker, C. Wrenn, and M. Murbach

NSF/NIST 10/19/00

Bragg focusing

Source

Sample

Rowland Circle

Focusing Monochromator

Focusing Monochromator

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Doubly Focusing Monochromator

Design by Stephen Smee, G. Scharfstein et al.

NSF/NIST 10/19/00

Blade profile chosen so blades form arc when compressed

Slope Error- SN: 072100011

-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

0 100 200 300 400

x (mm)E

rror

(d

eg)

R=10660 mm

R=6046 mm

R=2659 mm

R=1503 mm

R=921 mm

Flat Blade Fit

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0 100 200 300 400

x (mm)

Def

lect

ion,

v (

mm

)

Const_Rad

Flat-Blade

Var. Thick.

R= 915 mm

S. Smee et al. Provisional patent pending (2000)

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Focusing mechanics is out of beam

Vertical Horizontal

Design by Stephen Smee, G. Scharfstein et al.

NSF/NIST 10/19/00

Prototype performance

2 cmJHU IDG photo, prototype, and measurement

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Constrained optimization : crystal mosaic

Flux versus mosaic at fixed 0.2 meV energy resolution

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Effects of cystal misalignment

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Projected performance analytical approximation

C. Broholm, Nucl. Instr. Meth. A 369 169-179 (1996)

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Monte Carlo Simulation of MACS

Y. Qiu and C. Broholm to be published (2000)

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Resolution: Analytical and Monte Carlo simulations.

Y. Qiu and C. Broholm to be published (2000)

NSF/NIST 10/19/00

Multiplexing crystal analyzer system

Design by C. Brocker

One of twenty channels

BeO filterBeO filter

Be filterBe filter

PG filterPG filterCollimator 2Collimator 2

Collimator 1Collimator 1

8o vertically focusingAnalyzer crystals

8o vertically focusingAnalyzer crystals

“TAS” detector“TAS” detector

Energy integratingDetector

Energy integratingDetector

Design by C. Brocker

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Fixed vertical focusing of analyzers

Double analyzer is “compound lens” efficient vertical focusing

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Constant energy transfer slice

ki

kf

Q

meV 1meV7.3 fE

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Assembling slices to probe Q-E volume

0 meV0 meV

1 meV1 meV

2 meV2 meV

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Projected data collection times

Powder sample Q-E map 8 x 30 pts x 0.2 min. = 1:00

Single crystal constant-E slice 8 x 100 pts x 0.5 min. = 6:40

Single crystal complete Q-E Volume 8 x 100 x 10 pts x 0.5 min.= 3 days

CuHpCl

SCGO

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Scientific Program for NG0 spectrometer

Expanding the scope for Inelastic scattering from crystals: 0.5 mm3 samples impurities at the 1% level complete surveys to reveal spin-wave-conduction electron

interactions extreme environments: pressure and fields to tune correlated

systems

Probing short range order solid ionic conductors, spin glasses, quasi-crystals, ferroelectrics,

charge and spin polarons, quantum magnets, frustrated magnets.

Weak broken symmetry phases Incommensurate charge, lattice, and spin order in correlated

electron systems

Excitations in artificially structured solids Spin waves in magnetic super-lattices magnetic fluctuations in nano-structured materials

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Probing hole wave function in oxide : 1 D 2D?

Y2-xCaxBaNiO5

Xu, Aeppli, Broholm, et al. Science (2000)

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NSF Share (50%) of the Construction of MACS

1 2 3 4 50

50

100

150

200

250

300

350

400

Scientists

Design

Assembly

Equipment

Design&

Construction

Design Construction&

Design

Construction&

Assembly

Assembly&

Commissioning

$k

NSF/NIST 10/19/00

Conclusions Large solid angle access to NCNR cold source enables a

unique cold neutron spectrometer. MACS employs Bragg optics to focus the beam and provide

> 108 n/cm2/s on the sample at 0.2 meV resolution. The MACS detector concept offers the versatility,

resolution, and low background of a TAS with 20 times greater data rate.

The highly efficient constant E mode of MACS will provide a unique capability for probing the structure of fluctuating systems.

MACS will be complementary to the DCS and future SNS TOF spectrometers because of its unique data collection protocol

NSF partnership is needed to realize the potential and make the unique capabilities available to widest possible cross section of the US scientific community