pins workshop

PINS workshopPINS workshop

VITESS – Simulations for the HYSPEC polarization options

Brookhaven, April 6-7, 2006

U. Filges, P. Allenspach, J.Stahn Paul Scherrer Institute (PSI), Switzerland

Introduction

content of presentation - cross-check/intercomparison (between VITESS and NISP) to the

HYSPEC supermirror transmission polarizer option - S- bender polarizer configuration for the reflected neutron beam- wedge-bender polarizer configuration for the transmitted neutron

beam

PINS workshopBrookhaven, April 6-7, 2006

MC- packages

- the programs VITESS and McStas are used at PSI- VITESS 2.6 contains several different polarizer components like a polarizing bender or He-3 polarizer - presently McStas doesn’t include polarizer components


HYSPEC - Supermirror-bender transmission polarizer

starting point was a cross-check/intercomparison between the NISP and VITESS packages

I.Zaliznyak et al. Physica B 356 (2005) 150-155

setup of the transmission polarizer

horizontal profiles of the neutron intensity at the detector for

3.7, 10 and 20 meV

PINS workshopBrookhaven, April 6-7, 2006 Main values of VITESS setup

source size 2x2 cm; = 1 %

upstream collimator: 20 minutes; dimension: 2x12x15 cm (WxHxL)

distance source – upstream collimator: 40 cm

distance source – bender: 55 cm

bender configuration: dimension 2x12x5 cm; r=500cm; 80 Si-blades coated with m=3 R=77% (spin up) and m=1 (spin down);

distance source – detector: 450 cm

Energy 3.7 meV with =0.3ºPINS workshopBrookhaven, April 6-7, 2006

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VITESS - E = 3.7 meV º supermirror-transmission bender configuration

total neutrons spin up neutrons spin down neutrons

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theta – tilt angle between collimator and bender axes

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total neutrons

spin up neutrons

spin down neutrons

NISP - E = 3.7 meV º supermirror-transmission bender configuration

- differences: absorption of Si-wavers ; using different reflectivity curves


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VITESS - E = 10 meV º supermirror-transmission bender configuration


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NISP - E = 10 meV º supermirror-transmission bender configuration

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- very small differences in the shape of the reflected beam

Energy 10 meV with =0.1º

PINS workshopBrookhaven, April 6-7, 2006 Energy 20 meV with =0º

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- small differences in the shape and scaling factor for the transmitted neutron beam

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Influence of Reflectivity on the Detector Profile

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neutron total spin up neutrons R=90% spin down neutrons spin up neutrons R=77 %

VITESS - E = 20 meV .2º supermirror-transmission bender configuration R=90%

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PINS workshopBrookhaven, April 6-7, 2006 Detector Profiles for E = 25 meV

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- very complicated to split reflected and transmitted beam (also for higher theta)

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VITESS - E = 25 meV .1º supermirror-transmission bender configuration


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Dependency of the Detector Profile from the Sample Size

Conclusion

separation of spin up and spin down neutrons over a big energy range is very complicated

cross-check shows a very good agreement

presently defuse scattering and waviness of supermirrors are not included

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1.0 2.0 x 2.0 cm

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VITESS - E=20 meV .2º BNL-Bender configuration

comparison of different sample sizes - spin up neutrons

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comparison of spin up neutron beam for

different sample sizes

PINS workshopBrookhaven, April 6-7, 2006 S-shaped Supermirror Bender

spin up and spin down neutrons will be measured subsequently

transmitted neutron beam will be absorbed in a gadolinium layer (approx 50 m) behind supermirror layer

each useful neutron makes two reflections

upstream collimator right-curved supermirrorbender

left-curved supermirrorbender


VITESS setup for the S-Bender configuration





bender configuration: dimension 2x12x10 cm; r1=500 cm; r2=-500 cm; 80 Si-blades coated with m=3 R=77% (spin up) and m=0.1 (spin down);


PINS workshopBrookhaven, April 6-7, 2006 Detector profiles for 3.7 and 15 meV

tilt angle: 0.3in both cases

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2x104

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6x104VITESS - E=15 meV .3º S-Bender configuration


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2x104

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6x104VITESS - E=3.7 meV .3º S-Bender configuration


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PINS workshopBrookhaven, April 6-7, 2006 Detector profiles for 20 and 25 meV

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2.5x104VITESS - E=25 meV .3º S-Bender configuration


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VITESS - E=20 meV .3º S-Bender configuration


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tilt angle: 0.3in both cases

PINS workshopBrookhaven, April 6-7, 2006 Detector profile without Gadolinium

Conclusion

fixed tilt angle for the full energy range from 3.7 to 25 meV

no contamination

disadvantage: polarization efficiency; some loss in intensity; factor 4

but present setup not optimized on

intensity

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2.0x105VITESS - E=15 meV .3º S-Bender configuration without GD


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Wedge-shaped supermirror Bender

spin up and spin down neutrons will be measured subsequently

transmitted neutron beam will be measured – reflected neutron beam will be absorbed by the downstream collimator

increasing of the acceptance angle through wedge shape of the Si-waver

upstream collimator downstream collimator

wedge-shaped supermirrorbender


VITESS setup for thewedge-supermirrror bender configuration





bender configuration: dimension 2x12x10 cm; r=500 cm;80 Si-blades coated with m=3 R=77% (spin up) and m=0.1 (spin down); each Si-plate: width at entry side 0.25 mm – width at exit side 0.28 mm (curved wedge)


downstream collimator: 10 minutes

PINS workshopBrookhaven, April 6-7, 2006 Detector profiles for 3.7 and 10 meV

- S-bender has been tilted with 0.2in both cases

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8x104VITESS - E=10 meV .2º wedge-bender configuration


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8x104VITESS - E=10 meV .2º wedge-bender configuration


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Detector profiles for 20 and 25 meV

- S-bender has been tilted with 0.2in both cases

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1x104

2x104

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VITESS - E=25 meV .2º wedge-bender configuration


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3.5x104VITESS - E=20 meV .2º wedge-bender configuration


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Improvement of the Detector Profile for Higher Energies

Conclusion

also fixed tilt angle for the full energy range from 3.7 to 25 meV

Small contamitaions in the low energy range (up to 20 meV)

polarization efficiency higher as S-bender configuration

present setup not optimized on intensity/contaminations in the higher

energy range >20 meVsupermirror coating for spin up neutrons

was increased to m=4

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6x104VITESS - E=25 meV .2º wedge-bender configuration m= 4


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PINS workshopBrookhaven, April 6-7, 2006 Summary

subsequent measurement of the spin states covers a bigenergy range with very good polarization – especiallyusing the S-bender configuration

cross-check shows a good agreement between the MC-packages NISP and VITESS

analysis of simultaneously measured spin up/spin down neutrons can be sophisticated

certainly the polarization efficiency can be improved for the supermirror S-Bender and wedge bender configurations

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