HYSPEC IDT Polarized Beam Operation of the Hybrid Spectrometer at the pulsed Spallation Neutron...
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Transcript of HYSPEC IDT Polarized Beam Operation of the Hybrid Spectrometer at the pulsed Spallation Neutron...
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
HYSPECHYSPECIDTIDT
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
ither
mal
epith
erm
alsu
bthe
rmal
subt
herm
alth
erm
alth
erm
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HYSPECHYSPECIDTIDT
Neutron spectrum produced by SNS vs reactorNeutron spectrum produced by SNS vs reactor
0 20 40 60 80 100108
109
1010
Neu
tron
curr
ente
nter
ing
the
guid
e(n
/s)
Incident neutron energy Ei (meV)
Neutron current through 4x12cm guide entrance at 1.5 m from the moderator within E/E=2%
i
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
HYSPECHYSPECIDTIDT
0 20 40 60 80 100
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1CNCS model based on "Optimization...",J.V.Pearce et al. 2G.Granroth, Private communication
Ne
utro
n flu
x on
sam
ple
(n/s
/cm
2 )
E (meV)
HYSPEC (no offset), coupled H2
CNCS1, coupled H2
ARCS2, H2O
HRCS2, H2O
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)
HYSPECHYSPECIDTIDT
Layout of the SNS instrument suite - 2004 Layout of the SNS instrument suite - 2004
HYSPECHYSPECIDTIDT
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
HYSPECHYSPECIDTIDT
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
HYSPECHYSPECIDTIDT
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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Intensity (counts in 1 min)
Intensity (counts in 80 min)
nuclear, (2 ,0,0)
F lipper off
m agnetic, (2 /3,0,0)
F lipper on
x-p ixe l x-p ixe l
y-pi
xel
y-pi
xel
HYSPECHYSPECIDTIDT
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
HYSPECHYSPECIDTIDT
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.
HYSPECHYSPECIDTIDT
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
-10 -5 0 5 10 15 20
0
50
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150
200Neutron energy 15meV
Inte
nsi
ty(a
rb.u
nits
)
Detector X co-ordinate (cm)
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
HYSPECHYSPECIDTIDT
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.
-20 -15 -10 -5 0 5 10 15 20
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E=15meV, sample-detector distance=3.0m
Inte
nsi
ty(a
rb.u
nits
)
X co-ordinate (cm)
total m=0.6 m=3.0
-20 -15 -10 -5 0 5 10 15 20-50
0
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350
400E=15meV, sample-detector distance=3.5m
Inte
nsity
(X)
X co-ordinate(cm)
totalm=0.6m=3.0
-20 -15 -10 -5 0 5 10 15 20-50
0
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E=15meV, sample-detector distance=4.0m
Inte
nsity
(X)
X co-ordinate (cm)
total m=0.6 m=3.0
-20 -15 -10 -5 0 5 10 15 20
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Inte
nsi
ty(a
rb.u
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)
X co-ordinate (cm)
total m=0.6 m=3.0
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
HYSPECHYSPECIDTIDT
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)
HYSPECHYSPECIDTIDT
-20 -15 -10 -5 0 5 10 15 20
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700 alpha=1.2 total ba364 ba363
X Co-ordinate(cm)
I(x)
-20 -15 -10 -5 0 5 10 15 20
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700 alpha=0.80 total ba356 ba355
I(x)
X Co-ordinate (cm)
Optimizing polarizer tilt angle at E = 3.7 meVOptimizing polarizer tilt angle at E = 3.7 meV
-20 -15 -10 -5 0 5 10 15 20
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I(x)
X Co-ordinate(cm)
alpha=0.15 total ba338 ba337
-20 -15 -10 -5 0 5 10 15 20
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500
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700 alpha=0.30
total ba342 ba341
X Co-ordinate(cm)
I(x)
= 0.15° = 0.3°
= 0.8° = 1.2°
Neutron beam profiles on the detector
20’ collimatorin front
HYSPECHYSPECIDTIDT
Optimizing polarizer tilt: E = 3.7 meV is quite “forgiving”Optimizing polarizer tilt: E = 3.7 meV is quite “forgiving”
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.40.0
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1.1Incident energy 3.7 meV, bend angle (beta) 0.57 degrees
Pol
ariz
atio
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elat
ive
Inte
nsity
Tilt angle alpha (degrees)
Is/(Is+Id)Id/(Is+Id)PsPd
0.0
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Straight beam Deflected beam
HYSPECHYSPECIDTIDT
-20 -15 -10 -5 0 5 10 15 20
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X Co-ordianate (cm)
-20 -15 -10 -5 0 5 10 15 20
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3000 alpha=0.3 total ba301 ba302
I
X Co-ordinate (cm)
-20 -15 -10 -5 0 5 10 15 20
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3000 alpha=0.4 total ba305 ba306
I
X co-ordinate(cm)
-20 -15 -10 -5 0 5 10 15 20
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1500
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3000alpha=0.5
total ba313 ba314
I
X Co-ordinate (cm)
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
HYSPECHYSPECIDTIDT
-20 -15 -10 -5 0 5 10 15 20
0
500
1000
1500
2000
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3000 alpha=0.4 total ba331 ba332
X Co-ordinate (cm)
I
-20 -15 -10 -5 0 5 10 15 20
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3000 alpha=0.2 total ba319 ba320
X Co-ordinate (cm)
I
-20 -15 -10 -5 0 5 10 15 20
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alpha=0.0 total ba321 ba322
I
-20 -15 -10 -5 0 5 10 15 20
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3000 alpha=0.3 total ba327 ba328
X Co-ordinate (cm)
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
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70.0
0.1
0.2
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1.1Incident energy 20 meV, bend angle (beta) 0.57 degrees
Pol
ariz
atio
n/R
elat
ive
Inte
nsity
Tilt angle alpha (degrees)
Is/(Id+Is) Id/(Id+Is) Ps Pd
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Optimizing polarizer tilt: fine tuning is needed for higher Optimizing polarizer tilt: fine tuning is needed for higher energiesenergies
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70.0
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1.1Incident energy 10 meV, bend angle (beta) 0.57 degrees
Pol
ariz
atio
n/R
elat
ive
Inte
nsity
Tilt angle alpha (degrees)
Is/(Is+Id)Id/(Is+Id)PsPd
0.0
0.1
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Straight beam
Deflected beam
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
HYSPECHYSPECIDTIDT
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