nmi3 meeting, isis, september 26-29, 2005 contents: overview of new capabilities of the restrax...

NMI3 meeting, ISIS, September 26-29, 2005

Contents:

• Overview of new capabilities of the RESTRAX software

• Numerical optimizations of TAS parameters

• Virtual TAS experiments - simulations with selected sample kernels

Recent developments of RESTRAX Optimization of neutron optics and virtual triple-axis

experiments

Jan Šaroun1, Jiří Kulda2, Vasyl Ryukhtin1

1Nuclear Physics Institute, Řež2Institute Laue-Langevin, Grenoble

RESTRAX homepage::http://omega.ujf.cas.cz/restrax/

http://omega.ujf.cas.cz/restrax/

SIMRES

Version for instrument optimizations

- more detailed simulation of TAS components - mapping neutron beam in phase-space- tools for numerical optimization


SIMRES - virtual triple axis spectrometer

collimator segments

source

sample

crystals

detector

+ setups that can be mapped onto a classical TAS layout (powder and strain diffratometers)

multi-purpose components:

source: arbitrary energy, spatial and angular distributions via look-up tables

crystals: focusing arrays of elastically bent or mosaic crystals (incl. simulated extinction effects, absorption, etc...)

collimators: universal components describing:Sollers, curved guides or benders, elliptic or parabolic guides, lobster-eye devices

multiplexing: flat-cone multianalyzer and multidetector systems


Ray-tracing & numerical optimizations

Fixed setup fast ray-tracing code, 103 -104 counts/sec

ray-tracing results are used to find extremum of fm numerically.

figure of merit, fm(a1, a2, ...):I ... incident intensityE ... energy spreadI / E, I / E2 ... inelastic scatteringI / , I /2 ... diffraction

free parameters, a1, a2, ... an

crystal curvature, mosaicity, cutting angle,guide dimensions, curvature, divergence, ...

Speed problem: number of simulations / iteration = 1+2n2 n 4 acceptable (CPU time < 1 hour)


Lobster-eye device & focusing monochromator

)sin( BX Rf

spatial focusing

Rl

B

monochromatic beam + spatial focusing

0 B

?

Simultaneous optimization of the crystal curvatures and guide parameters – mutual correlations– ray-tracing: realistic model of the instrument components

)sin(2 BE Rf

monochromatic focusing

0 B



50 cm30 cm

50 cm

8 cm

12.5

Lobster-eye device• 20 (hor.) or 30 (ver.) blades• thickness 0.5 mm• m=3 supermirror (concave sides)• elliptic & parabolic profiles• optimization: entry & exit width

TAS - IN14 setup• cold source• straight 58Ni guide, 6x12 cm2

• monochromator: PG 002, doubly focusing, =4.05 Å

• target (sample) area: 3x3 mm2

• optimization: crystal curvatures


Parabolic guide

Focusing on small samples

400 200 0 200 400

40

20

0

20

40

55

55

fp

mm

550LS

mm

z

mm

ttz

mm

LL

mm

+ perfect focusing of a parallel beam

- large reflection angle at the entry


Focusing on small samples

400 200 0 200 400

50

0

5055

55

fp

mm

550LS

mm

z

mm

ttz

mm

LL

mm

Elliptic guide

- parallel beam does not focus to a point

+ lamellae are parallel at the entry



Optimization in 2 dimensionsx

Mapping the parameter space

horizontal:1) monochromator: 1/RH

2) guide: exit width

vertical:1) monochromator: 1/RV

2) guide: exit height

adjustable parameters:

Resolution 32x32 pixels 1024 simulations

Number of blades is fixed adjusting focal distance


Mapping of parameter space

Elliptic bladesOptimization route in 2 dimensions

-0.2 0.0 0.2 0.440

50

60

70

80

90

H [m-1]

exit

wid

th [m

m]

0.0 0.2 0.4 0.670

80

90

100

110

120

V [m-1]

exit

heig

ht [m

m]

Intensity/E Intensity

horizontal vertical


Mapping of parameter space

-0.2 0.0 0.2 0.440

50

60

70

80

90

H [m-1]

exit

wid

th [m

m]

0.0 0.2 0.4 0.670

80

90

100

110

120

V [m-1]

exit

heig

ht [m

m]

Parabolic bladesOptimization route in 2 dimensions

Intensity/E Intensity

horizontal vertical



Optimization in 3 dimensions

horizontal:1) monochromator: 1/RH

2) guide: entry width3) guide: exit width

vertical:1) monochromator: 1/RV

2) guide: entry height3) guide: exit height

adjustable parameters:

mapping in 3D is not feasible 32768 simulations/map …

Number of blades is fixed adjusting focal distance and spacing between blades



Optimization in 3 dimensionsElliptic blades

-30 -20 -10 0 10 20 30-30

-20

-10

0

10

20

30

x [mm]

y [m

m]

-0.08 -0.04 0.00 0.04 0.08-0.08

-0.04

0.00

0.04

0.08

kx/k

k y/k



Optimization in 3 dimensions

-30 -20 -10 0 10 20 30-30

-20

-10

0

10

20

30

x [mm]

y [m

m]

-0.08 -0.04 0.00 0.04 0.08-0.08

-0.04

0.00

0.04

0.08

kx/k

k y/k

Parabolic blades



Optimization in 3 dimensionsFocusing monochromator only

-30 -20 -10 0 10 20 30-30

-20

-10

0

10

20

30

x [mm]

y [m

m]

-0.08 -0.04 0.00 0.04 0.08-0.08

-0.04

0.00

0.04

0.08

kx/k

k y/k



Optimization in 3 dimensionsResults

Total intensity (whole beam) [109/s]:

parabolic 1.3elliptic 1.6no 3.4

RESTRAX

Version for TAS resolution simulations and data analysis

- simplified TAS setup with faster ray-tracing code - 4D resolution functions + convolution with S(Q,)- dynamically loaded modules with S(Q,) model- non-linear data fitting


Sample “exchanger” in RESTRAX

TAS ray-tracing, R(Q,)

4D convolution

• data simulation• data fitting

dynamically loaded modules, S(Q,)

• Damped harmonic oscillators • Damped harmonic oscillators, free

dispersion gradient• Bond charge model (phonons in Si, Ge, ...)• Incommensurate fluctuations (diffuse

satellites)• … others defined by users


TAS: conventional arrangement

monochromator

sample

analyzer

detector


TAS: flat-cone analyzer

monochromator

sample

analyzer

detector


TAS: flat-cone multianalyzer

monochromator

sample

analyzer

detector


Sweeping reciprocal space

New flat-cone analyzer for ILL TAS instruments, 32 channelsIN20: monochromator Si, ki=3 A-1

0 1 2 3-2

-1

0

1

2

3

[

0 1

0]

E=0 meV

0 1 2 3

E=4 meV

[1 0 0]0 1 2 3

E=12 meV

non-linear scans in rec. lattice

a3

a4


Example 1: Incommensurate sattelites

Incommensurate sattelites: E

210

010

200

210000

010110

E

raw data10 20 30 40 50 60 70 80

-40

-20

0

20

40

E=4 meV

a4 [deg]

a3 [d

eg]

M.C. ray-tracing & convolution with S(Q,E)


Example 1: Incommensurate satellites

0 1 2 3-2

-1

0

1

2

3

[0

1 0]

E=0 meV

0 1 2 3

E=4 meV

[1 0 0]0 1 2 3

E=12 meV

... and transformed to rec. lattice space


Example 1: Incommensurate satellites

detail ...


Example 2: bond charge model (BCM)

Model describing phonons in diamond lattice (Si, Ge, -Sn, ...)Eigenvalues & eigenvectors are calculated using coulombic potential of bond charges for each of Q,E points representing simulated TAS resolution functionW. Weber, Phys. Rev. B 15 (1977) 4789.

phonons in Si


Phonons in Si

E=10 meV E=20 meV


Phonons in Si

E=30 meV E=40 meV


Phonons in Si

E=50 meV E=60 meV


E=20 meV

Phonons in Si

MC simulation for IN20kf=3A-1, E=20meV64 channels, a4=1.25o

91 steps, a3=0.75o

convolution with flat-cone resolutionsimulated by ray-tracingCPU time: 4 hours


Summary

Numerical optimizations• using ray-tracing simulations in numerical optimization is feasible

• multiple correlated TAS parameters can be optimized with respect to different figures of merit

Lobster-eye guides• high flux at small samples, leaves space for sample environment

• vertical and horizontal focusing can be splitted in 2 guide sections

• alternative to focusing monochromators at quasiparallel beams

Dynamically loaded S(Q,) modules• data simulations and fitting with various sample kernels

• extensions provided by users

RESTRAX homepage::http://omega.ujf.cas.cz/restrax/

http://omega.ujf.cas.cz/restrax/

nmi3 meeting, isis, september 26-29, 2005 contents: overview of new capabilities of the restrax...

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