HYSPECHYSPECIDTIDT

Polarized Beam Operation of the Hybrid Spectrometer at Polarized Beam Operation of the Hybrid Spectrometer at the pulsed Spallation Neutron Source.the pulsed Spallation Neutron Source.

OutlineOutline

• HYSPEC: project timeline and place in the SNS instrument suite

• HYbrid SPECtrometer’s layout and principal features

• Polarized beam setup: principle and components

• Performance optimization of the (Fe/Si) transmission polarizer

• Summary and open questions

Igor ZaliznyakIgor ZaliznyakNeutron Scattering Group, Brookhaven National Laboratory

HYSPEC Instrument Design Team

V. Ghosh, L. Passell and S. Shapiro (BNL), M. Hagen (SNS)

HYSPECHYSPECIDTIDT

20002000– Concept of the Hybrid Spectrometer proposed at BNLConcept of the Hybrid Spectrometer proposed at BNL

20012001– Direct Geometry Hybrid Spectrometer presented to SNS EFACDirect Geometry Hybrid Spectrometer presented to SNS EFAC

– HYSPEC Instrument Development Team (IDT) formed HYSPEC Instrument Development Team (IDT) formed

20022002– HYSPEC IDT filed Letter of Intent with SNSHYSPEC IDT filed Letter of Intent with SNS

– HYSPEC proposal submitted to DOEHYSPEC proposal submitted to DOE

20032003– DOE CD0, HYSPEC is approved as part of the SING projectDOE CD0, HYSPEC is approved as part of the SING project

20042004– HYSPEC’s placement approved, design&engineering: real work begins HYSPEC’s placement approved, design&engineering: real work begins

20052005– DOE CD2, HYSPEC’s performance baseline approvedDOE CD2, HYSPEC’s performance baseline approved

20062006– DOE CD3, construction begins DOE CD3, construction begins

20112011– CD4, commissioning & beginning of operationCD4, commissioning & beginning of operation

HYSPEC’s timelineHYSPEC’s timeline

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HYSPEC Teams.HYSPEC Teams.

S. M. Shapiro, co-PI BNLI. Zaliznyak, co-PI BNLD. Abernathy SNSL. Daemen LANLB. Gaulin McMasterJ. Gardner BNLV. Ghosh BNLM. Greven StanfordM. Hagen SNSK. Hirota ISSPV. Kiryukhin RutgersY. Lee MITC. Majkrzak NISTR. MQueeney Ames/Iowa St. U.S. Nagler ORNLR. Osborn ANLL. Passell BNLL. P. Regnault ILLJ. Rhyne U. MissouriJ. Tranquada BNLG. Xu BNLA. Zheludev ORNL

IDT Members and their AffiliationsIDT Members and their Affiliations

• I. Zaliznyak (BNL)

• S. M. Shapiro (BNL)

• L. Passell (BNL)

• V. J. Ghosh (BNL) Monte-Carlo simulations

• W. Leonhardt (BNL) Project Engineer

• M. Hagen (SNS/BNL) Instrument scientist

Instrument Design TeamInstrument Design Team

http://neutrons.phy.bnl.gov/HYSPEC

• S. M. Shapiro, PI (BNL)

• I. Zaliznyak, PI (BNL)

• L. Passell (BNL)

• R. McQueeney (Ames/Iowa St. U.)

• J. Rhyne (LANL)

• J. Tranquada (BNL)

IDT Executive CommitteeIDT Executive Committee

HYSPECHYSPECIDTIDT

High resolution and low energy transferHigh resolution and low energy transfer10-100 10-100 eV Multichopper SpectrometereV Multichopper Spectrometer

• E = 2 - 20 meVE = 2 - 20 meV• Q = 0.1 - 4 Q = 0.1 - 4 Å-1

High energy transferHigh energy transfer10-1000 meV Fermi Chopper Spectrometer10-1000 meV Fermi Chopper Spectrometer

• E = 10 - 1000 meVE = 10 - 1000 meV• Q = 0.1 – 22 Q = 0.1 – 22 Å-1

High intensity at moderate resolution and medium High intensity at moderate resolution and medium energy transfer + polarized beamenergy transfer + polarized beamCrystal-Focussing Crystal-Focussing HyHybrid brid SpecSpectrometertrometer

• E = 2.5 - 90 meVE = 2.5 - 90 meV• Q = 0.1 – 8 Q = 0.1 – 8 Å-1

CNCSCNCS

HYSPECHYSPEC

ARCSARCS

HYSPEC’s place in the SNS inelastic instruments suite.HYSPEC’s place in the SNS inelastic instruments suite.ep

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Neutron spectrum produced by SNS vs reactorNeutron spectrum produced by SNS vs reactor

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Neutron current through 4x12cm guide entrance at 1.5 m from the moderator within E/E=2%

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20 K coupled H2 (NISP interpolation) 20 K coupled H2 (MCSTAS interpolation) H2O (MCSTAS interpolation) MC calculation by E. Iverson

NIST cold sourcenormalized to same intensity at low E MC calculation for

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1CNCS model based on "Optimization...",J.V.Pearce et al. 2G.Granroth, Private communication

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HYSPEC (no offset), coupled H2

CNCS1, coupled H2

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Comparison of the HYSPEC performance with other Comparison of the HYSPEC performance with other inelastic instruments planned for the SNSinelastic instruments planned for the SNS

MCSTAS simulations by HYSPEC IDT (V. Ghosh), with different re-scaling for ARCS and SEQUOIA

CNCS, ARCS and HRCS intensities were re-scaled tothe same, coarser energy resolution as HYSPEC (this over-estimates their actual intensity)

MC simulations by SNS (G. Granroth and D. Abernathy)

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Layout of the SNS instrument suite - 2004 Layout of the SNS instrument suite - 2004

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HYSPEC layout and principal featuresHYSPEC layout and principal features

To get more information, and for the project updates, please, visit http://neutrons.phy.bnl.gov/HYSPEC

T0 Chopper

T2 Chopper

Monochromator

Goniometer

Radial Collimatoror Bender Polarizers

Flight Chamber (Ar/He filled)

Detectors

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HYSPEC layout in the polarized beam modeHYSPEC layout in the polarized beam mode

18-20 transmission polarizers2cm x 5cm (WxL) with 20’ Soller collimators upfront

Heusler crystal monochromator,vertically focussed

neutron spin flipper

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HYSPEC polarization analysis: principle and experimental HYSPEC polarization analysis: principle and experimental demonstration on SPINS at NISTdemonstration on SPINS at NIST

S.-H. Lee, C. F. Majkrzak, Physica B 267-268, 341 (1999)Heusler

Polarized beam Measurement with a Position Sensitive Detector (PSD)

HYSPECHYSPECIDTIDT

HYSPEC polarization analysis: experimental demonstration HYSPEC polarization analysis: experimental demonstration with PSD on SPINSwith PSD on SPINS

Nuclear and magnetic scattering intensities in La5/3Sr1/3NiO4

I. A. Zaliznyak and S.-H. Lee, in Modern Techniques for Characterizing Magnetic Materials, ed. Y. Zhu (to be published by Kluwer Academic, 2004)

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F lipper off

m agnetic, (2 /3,0,0)

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x-p ixe l x-p ixe l

y-pi

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HYSPEC setup for polarization analysisHYSPEC setup for polarization analysis

Polarized incident beam is supplied by reflection from the vertically focusing Cu2MnAl (Heusler alloy) crystal monochromator

10 meV < E10 meV < Eiipolpol < 90 meV < 90 meV

Polarization analysis of the scattered neutrons is performed by a set of 18-20 supermirror-bender transmission polarizers, each 2 cm wide, 5 cm thick and 15 cm high,

3.7 meV < E3.7 meV < Effpolpol < 15-25 meV < 15-25 meV

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Most important question: can we expect the transmission Most important question: can we expect the transmission polarizers to work up to 15-25 meV?polarizers to work up to 15-25 meV?

Performance of an optimized Fe/Si transmission polarizer for ~15 meV C. Majkrzak, Physica B 213&214 (1995)

Yes, but fine-tuning of the polarizer tilt angle is necessary.

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MC simulation (NISP) of HYSPEC operation in the MC simulation (NISP) of HYSPEC operation in the polarized beam mode: beam separationpolarized beam mode: beam separation

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Bender width = 2cm All neutrons Spin up neutrons Spin down neutrons

Simulation for the bender geometry optimized for E=14.7 meV (C. Majkrzak, 1995) Sample-to-detector distance LSD is 4.5 m

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The spatial separation of two polarizations for different The spatial separation of two polarizations for different sample-to-detector distancessample-to-detector distances

θc(up) = 3.0 θc

Ni,

θc(down) = 0.6θc

Ni.

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total m=0.6 m=3.0

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The two polarizations only become sufficiently separated that they can be measured cleanly in the adjacent detector tubes for values of the secondary flight path LSD > 4.0m.

LSD = 3.0m LSD = 3.5m

LSD = 4.0m LSD = 4.5m

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R

d

stra ight-transm itted“spin-dow n”

1 bounce“spin-up”

2 bounces“spin-up”

unpolarized incident neutron beam

transm ission polarizer

Optimizing geometry of the single-bounce transmission Optimizing geometry of the single-bounce transmission polarizerpolarizer

Defining parameters are:

• θc(up) and θc

(down) • L, length• d, channel width• , tilt angle• β, bend angle• L ≈ 2R sin(β/2)≈ R β

Optimization considerations and constraints

• θc(up) = 3.0 θc

(Ni), θc(down) = 0.6 θc

(Ni), => best we can imagine for now• L≈ 50 mm => maximum length is constrained by the transmission through Si • d ≤ R(1- cosβ) ≈ Lβ/2 ≈ 0.25 mm => to remove the line-of-sight• polarizer bend angle β => mechanically constrained, currently use 0.57°• polarizer tilt angle => must be optimized

Simple optimization condition for a single-bounce device

( + β) = θc(up) = 3.0 θc

(Ni)

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Optimizing polarizer tilt angle at E = 3.7 meVOptimizing polarizer tilt angle at E = 3.7 meV

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= 0.15° = 0.3°

= 0.8° = 1.2°

Neutron beam profiles on the detector

20’ collimatorin front

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Optimizing polarizer tilt: E = 3.7 meV is quite “forgiving”Optimizing polarizer tilt: E = 3.7 meV is quite “forgiving”

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Optimizing polarizer tilt angle at E = 10 meVOptimizing polarizer tilt angle at E = 10 meV

= 0.1° = 0.3°

= 0.4° = 0.5°

Neutron beam profiles on the detector

20’ collimatorin front

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IOptimizing polarizer tilt angle at E = 20 meVOptimizing polarizer tilt angle at E = 20 meV

= 0.0° = 0.2°

= 0.3° = 0.4°

Neutron beam profiles on the detector

20’ collimatorin front

HYSPECHYSPECIDTIDT

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Optimizing polarizer tilt: fine tuning is needed for higher Optimizing polarizer tilt: fine tuning is needed for higher energiesenergies

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HYSPECHYSPECIDTIDT

A somewhat similar concept: D7 at ILLA somewhat similar concept: D7 at ILL

Important differences of the proposed HYSPEC setupImportant differences of the proposed HYSPEC setup– optimized for thermal neutrons optimized for thermal neutrons => => optimized for using the straight-through transmitted beam optimized for using the straight-through transmitted beam => => allows low-polarization-efficiency mode extending to high energies!allows low-polarization-efficiency mode extending to high energies! – both spin states are measured by the detector arrayboth spin states are measured by the detector array

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Summary and open questionsSummary and open questions

• Heusler monochromator provides polarized incident beam

• Scattered beam polarization is determined by the array of transmission

polarizers

– straight-through transmitted beam is always measured

– polarization sensitivity covers thermal neutron energies up to ~30 meV

– all scattering angles are covered, ~2/3 of detectors are efficiently used

– price in intensity paid for using 20’ collimators also buys lower background and

somewhat better q-resolution

– Fe/Si, Co/Si, other?

• Optimization of the polarizer geometry for broadband operation

– important to use the optimized tilt angle for every Ei, and E-range

– curvature choice (possibly straight stack)?

– fine tuning: length, channel width, collimation in front.

• Effect of a coarse (2-3 degrees) radial collimator behind the polarizers?

HYSPECHYSPECIDTIDT

Spallation Neutron Source (SNS) at ORNLSpallation Neutron Source (SNS) at ORNL

http://www.sns.gov/http://www.sns.gov/partnerlabs/partners.htm

HYSPECHYSPECIDTIDT

SNS accumulator ring built by BNLSNS accumulator ring built by BNL

http://sns.bnl.gov/http://sns.bnl.gov/ap_group/ring.html