HYSPEC - HYSPEC - Hy Hy brid brid Spec Spec trometer trometer for the Single Crystal and for the Single Crystal and Polarized Neutron Studies at Polarized Neutron Studies at the SNS the SNS Steve Shapiro and Igor Zaliznyak Steve Shapiro and Igor Zaliznyak Center for Neutron Scattering and Neutron Scattering Group Brookhaven National Laboratory Brookhaven National Laboratory • Unique in its class • Highest flux on small samples • Easily adapted for polarized neutron studies
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HYSPEC - HYSPEC - HyHybrid brid SpecSpectrometer for trometer for the Single Crystal and Polarized the Single Crystal and Polarized
Neutron Studies at the SNSNeutron Studies at the SNSSteve Shapiro and Igor ZaliznyakSteve Shapiro and Igor Zaliznyak
Center for Neutron Scattering and Neutron Scattering Group
Brookhaven National LaboratoryBrookhaven National Laboratory
• Unique in its class
• Highest flux on small samples
• Easily adapted for polarized neutron studies
OutlineOutline
• Motivation (SMS)• Science Case (SMS)• IDT and Budget (SMS)• Conceptual Design (IZ)• Performance and Comparison(IZ)• Summary (IZ)
StatusStatus Fall, 1999
BNL initiates an effort to design a spectrometer for the SNS December, 2000
Concept of the Hybrid Spectrometer formulated and adopted March, 2001
First presented to EFAC. Received positive reply Fall, 2001
Instrument Development Team formed October: Workshop on the Hybrid Spectrometer held at BNL Refined HYSPEC concept presented to EFAC
January, 2002 HYSPEC IDT filed Letter of Intent with SNS
April, 2002 Formal presentation to EFAC
July, 2002 Letter of Intent accepted; Submit Scientific Proposal to EFAC
MotivationMotivation
A and B category top priority - “potential day-one instrument”1 Report on the SNS Inelastic Neutron Scattering Workshop, SNS Document IS-1.1.8.2-8004-MM-A-00 (2000).
BS
HRCS
CNCS
ARCS
HYSPECHYSPEC
SNS Inelastic Neutron Scattering Workshop1
Argonne (11/99)
Motivation from WorkshopMotivation from Workshop
Small single crystal samples Focussing Bragg optics
Broad range of standard sample environments Use of collimators and beam definers Sample environment separate from detector vacuum
Low background Time of flight Sample area out of direct beam Use of collimators
Vector Q in single crystals Moveable detector and rotatable sample
Polarization Analysis Proven and maintenance-free technology
Motivation from WorkshopMotivation from Workshop
Page 5 of Report:
“This [high time averaged flux] opens up the possibility of utilizing triple-axis like methods to examine details of excitations when the important physics can be found at specific, well defined regions of Q and E space”
Recommended: “potential day-one instrument”
Science CaseScience Case
Quantum critical pointsLow-D magnetismNanomagnetism and complex systemsDisordered and weakly ordered phasesAnomalous phonon behaviorStrongly correlated electron systems
– Hi Tc: YBCO experiment performed at ILL - IN22
Polarized Neutron Study on Resonant Polarized Neutron Study on Resonant Mode in YBCOMode in YBCO6.85 6.85 (L.P. Regnault et al.)(L.P. Regnault et al.)
HYSPECHYSPEC: A Proposed Crystal-Time-of Flight : A Proposed Crystal-Time-of Flight HyHybrid brid SpecSpectrometer for the Spallation Neutron Sourcetrometer for the Spallation Neutron Source
Part 2: Conceptual design
T0 Chopper
Disc Chopper
Monochromator
Goniometer
Radial Collimator,or Bender Polarizers
Flight Chamber (evacuated or Ar/He filled)
Detectors
Why Hybrid Spectrometer?Why Hybrid Spectrometer?
Monochromator vertical focusingMonochromator vertical focusing gaingain on SPINS@NIST: factor ~3factor ~3 even for m = 19 gm = 19 g sample (below)
Science challengesScience challenges
• small samples
• subtle features
• polarization analysis
• small signals, background-limited measurements
Need intensity boostNeed intensity boost
II00
3 x I3 x I00
0 20 40 60 80 100108
109
1010
Ne
utr
on
cu
rre
nt
en
teri
ng
th
e g
uid
e (
n/s
)
Incident neutron energy Ei (meV)
Neutron current through 4x12cm2 guide entrance at 1.5 m from the moderator within E=2% of E
i
20 K coupled H2 (NISP interpolation)
20 K coupled H2 (MCSTAS interpolation)
H2O (MCSTAS interpolation)
MC calculation by E. Iverson
HYSPEC design choices: moderatorHYSPEC design choices: moderator
2.0*1012
1.6*1012
1.2*1012
0.8*1012
0.4*1012
0.0
20K H2 (decoupled)
Inte
nsi
ty (
n/s
R/μ
s/e
V/p
uls
e)
Coupled supercritical H2 moderator wins in thermal neutron range Ei<45meV
ambient H2O
0 100 200 300 400 500 600Time (μs)
Time-spectra of the neutron intensity from different moderators for EEii = 15.8 meV = 15.8 meV
Moderators useful neutron flux
coupled 20K H2
ambient H2O
Figure of merit is the total flux within t = 40-80 40-80 ss time window accepted by the spectrometer.
20K H2 (coupled)
HYSPEC design choices: energy resolutionHYSPEC design choices: energy resolutiontt t/tt/tff E/EE/Eff
For given incident pulse length t instrument energy resolution is determined by the analyzer flight-path
Sample and detector size contribution to the instrument resolution is less than 0.5% each
TOF analyzer energy resolution for the length of the secondary flight-path LLSDSD=4.5 m=4.5 m and pulse lengths 40 μs to 80 μs is in the range 1.7% to 15%
HYSPEC design choices: guide curvatureHYSPEC design choices: guide curvatureFlux on sample for different guide curvatures, parametrized by the corresponding offset at monochromator position.
Straight guide with m=3 supermirror coating is an optimal solution
0 20 40 60 80 100
105
106
107
HYSPEC flux simulated using MCSTASN
eut
ron
flux
on s
ampl
e (
n/s/
cm2 )
Energy(meV)
Beam offset at monochromator
0.0 cm 8.0 cm 12.0 cm 16.0 cm
HYSPEC performance: vertical focusing gainHYSPEC performance: vertical focusing gain
Crystal-monochromator hybrid spectrometer (HYSPEC, top scheme) vs traditional “straight-through” TOF setup (MCST, bottom scheme).
HYSPEC wins except at 5 meV, where both concepts are rougthly equal.HYSPEC wins except at 5 meV, where both concepts are rougthly equal.
0 20 40 60 80 1000
2
4
6
8
Inte
nsi
tyH
YS
PE
C/I
nte
nsi
tyM
CS
T
Energy (meV)
simulation with MCSTAS
HYSPEC performance: comparison with other HYSPEC performance: comparison with other inelastic instruments planned for the SNSinelastic instruments planned for the SNS
MC simulations by MCSTAS, V. Ghosh (2002)
CNCS, ARCS and HRCS intensities are re-scaled to HYSPEC energy resolution (such rescaling may over-estimate the actual intensity)
0 20 40 60 80 100
104
105
106
107
1CNCS model based on "Optimization...",J.V.Pearce et al. 2G.Granroth, Private communication
S.-H. Lee, C. F. Majkrzak, Physica B 267-268, 341 (1999)
Heusler
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
10meV < E10meV < Eiipolpol < 90meV < 90meV
Polarization analysis of the scattered neutrons is done by a set of 11-22 supermirror-bender transmission polarizers, each 2 cm wide, 5 cm thick and 15 cm high,
5meV < E5meV < Effpolpol < 25meV < 25meV
HYSPEC layout in the polarized beam modeHYSPEC layout in the polarized beam mode
HYSPEC performance in the polarized beam modeHYSPEC performance in the polarized beam mode
-10 -5 0 5 10 15 20
0
50
100
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
HYSPEC performance in the polarized beam modeHYSPEC performance in the polarized beam mode
0 5 10 15 20 25 30 350.0
0.2
0.4
0.6
0.8
1.0
Be
am
po
lari
zatio
n
Energy(meV)
Straight beam Deflected beam
HYSPEC place in the SNS inelastic instrument suiteHYSPEC place in the SNS inelastic instrument suite
Guide coating m = 3 m = 3.5 m = 3 – 3.5 m = 3 – 3.5
Guide Apertures (width x height, cm2)
entrance 4x12.8
main 4 x 15 exit 4 x 10
entrance 5 x 10main 5 x10 exit 1.5 x 5
SummarySummary
HYSPEC will be a unique resource for probing correlations in condensed matter for
E [5,90] meV∈E [5,90] meV∈ E/E [0.05,0.15]∈E/E [0.05,0.15]∈
Q [0.3,10] ∈Q [0.3,10] ∈ ǺǺ-1-1 Q/Q [0.005,0.2]∈Q/Q [0.005,0.2]∈ Worlds most intense thermal neutron beam at a pulsed sourceWorlds most intense thermal neutron beam at a pulsed source Can optimize range of energy transfer and resolutionsand resolutions for
experiment Independent variation of Q and E resolution Polarization analysis capabilityPolarization analysis capability
The ultimate questionThe ultimate question: Do we need HYSPEC?LeadLead: Do we need 2 to 5 times larger flux2 to 5 times larger flux on sample compared to other SNS spectrometers and a polarized beam optionpolarized beam option?Our answerOur answer: Yes, we do.
