Transcript Conceptual design for the high throughput cold

Conceptual design and performance of
high throughput cold spectrometer : MACS
Collin Broholm
Johns Hopkins University and NIST Center for Neutron Research
Why MACS
 Layout and key
elements
 Performance
 Data collection
 Scientific program
 Budget and schedule

MACS development team
Overall instrument design
Paul Brand
NIST
Christoph Brocker
NIST
Collin Broholm
JHU
Jeff Lynn
NIST
Mike Rowe
NIST
Jack Rush
NIST
Yiming Qiu
JHU
NSF/NIST 10/19/00
Focusing Monochromator
Steve Conard
JHU
Joe Orndorff
JHU
Tim Reeves
J
Gregg Scharfstein
J
Stephen Smee
UMD
Shielding Calculations
Charles M. Eisenhauer
Why cold neutrons and double focusing
• Q and E resolved spectroscopy requires
E  0.1 J
Q  0.1a1
• Energy scale J varies more than length scale a
Lattice
3D Cubic S=5/2
2D Square S=1/2
2D Kagomé S=3/2
2D Kagomé S=3/2
1D S=1/2 chain
1D S=1/2 chain
1D S=1 chain
1D S=1 chain
Compound
La0.7Pb0.3 MnO3
La2CuO4
KCr3(OH)6(SO4)2
SrCr9Ga3O19
Cu(C6D5COO)2.3D2O
KCuF3
NENP
AgVP2 S6
J (meV)
8.8
132
1.2
10
1.5
35
4.1
58
a (Å)
3.9
5.4
3.7
2.9
3.2
3.9
5.2
2.9
• To probe a range of materials must vary
Q  0.05 A1
102 meV  E  10 meV
keeping
• To probe hard matter with low energy scales
• Reduce Ei. Cold source provides the flux
• Increase
angular divergence before and after sample
NSF/NIST
10/19/00
Kinematic limits for neutron scattering
Efix and 2q range determine accessible Q-E space
NSF/NIST 10/19/00
Comparing TOF to TAS
• Can focus beams with Bragg optics
TAS like
• Can select range of energy transfer
• Can use reactor CW flux
• Larger detector solid angle
TOF like
• E-scan with “no” moving parts
• Can use pulsed spallation source peak
flux
NSF/NIST 10/19/00
NCNR Liquid Hydrogen cold source
  4.8 1013 n/cm2 / s
Teff  45 K
New cold source to be installed in 2001 will double flux
NSF/NIST 10/19/00
Overview of MACS
Design by C. Brocker, C. Wrenn, and M. Murbach
Bragg focusing
Focusing
Monochromator
Rowland Circle
NSF/NIST 10/19/00
Doubly Focusing Monochromator
Design
by Stephen
NSF/NIST
10/19/00Smee, G. Scharfstein et al.
Blade profile chosen so blades form arc when
compressed
Flat Blade Fit
Slope Error- SN: 072100011
0.20
30.0
Const_Rad
Flat-Blade
Var. Thick.
20.0
0.15
R=10660 mm
R=6046 mm
0.10
R=2659 mm
R=1503 mm
Error (deg)
Deflection, v (mm)
25.0
R= 915 mm
15.0
10.0
0.05
R=921 mm
0.00
0
100
200
-0.05
-0.10
5.0
-0.15
0.0
-0.20
0
100
200
300
400
x (mm)
S. Smee et al. Provisional patent pending (2000)
NSF/NIST 10/19/00
x (mm)
300
400
Focusing mechanics is out of beam
Vertical
Design
by Stephen
NSF/NIST
10/19/00Smee, G. Scharfstein et al.
Horizontal
Prototype performance
NSF/NIST 10/19/00
2 cm
JHU IDG photo, prototype, and measurement
Constrained optimization : crystal mosaic
Flux versus mosaic at fixed 0.2 meV energy resolution
NSF/NIST 10/19/00
Effects of cystal misalignment
NSF/NIST 10/19/00
Projected performance analytical approximation
NSF/NIST 10/19/00
C. Broholm, Nucl. Instr. Meth. A 369 169-179 (1996)
Monte Carlo Simulation of MACS
NSF/NIST 10/19/00
Y. Qiu and C. Broholm to be published (2000)
Resolution: Analytical and Monte Carlo
simulations.
NSF/NIST 10/19/00
Y. Qiu and C. Broholm to be published (2000)
Multiplexing crystal analyzer system
Design by C. Brocker
NSF/NIST 10/19/00
One of twenty channels
“TAS” detector
Collimator 1
Energy integrating
Detector
8o vertically focusing
Analyzer crystals
BeO filter
Be filter
PG filter
Collimator 2
Design by C. Brocker
Fixed vertical focusing of analyzers
Double
analyzer is “compound lens”
NSF/NIST 10/19/00
efficient vertical focusing
Constant energy transfer slice
E f  3.7 meV   1 meV
kf
ki
NSF/NIST 10/19/00
Q
Assembling slices to probe Q-E volume
2 meV
1 meV
0 meV
NSF/NIST 10/19/00
Projected data collection times
CuHpCl
Powder sample Q-E map
8 x 30 pts x 0.2 min. = 1:00
Single crystal constant-E slice
SCGO
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
NSF/NIST 10/19/00
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
NSF/NIST 10/19/00
Probing hole wave function in oxide : 1 D
2D?
Y2-xCaxBaNiO5
NSF/NIST 10/19/00
Xu, Aeppli, Broholm, et al. Science (2000)
NSF Share (50%) of the Construction of MACS
400
Scientists
Design
Assembly
Equipment
350
300
250
$k
200
150
100
50
0
1
Design
NSF/NIST 10/19/00
2
3
Design
Construction
&
&
Construction
Design
4
5
Construction
Assembly
&
&
Assembly Commissioning
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
NSF/NIST 10/19/00