oak ridge lab’s seop r&d efforts
DESCRIPTION
Oak Ridge Lab’s SEOP R&D Efforts. Wai Tung Hal Lee, Xin Tong (Tony), Joshua Pierce, Mike Fleenor, Valeria Hanson*, Akbar Ismaili **, J. Lee Robertson. Instrument Development Group, Neutron Facilities Development Division Oak Ridge National Laboratory Oak Ridge, TN 37831, USA - PowerPoint PPT PresentationTRANSCRIPT
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Oak Ridge Lab’s SEOP R&D Efforts
Wai Tung Hal Lee, Xin Tong (Tony), Joshua Pierce, Mike Fleenor, Valeria Hanson*, Akbar Ismaili **, J. Lee Robertson.
Instrument Development Group,Neutron Facilities Development DivisionOak Ridge National LaboratoryOak Ridge, TN 37831, USA
* Hamilton College** University of Tennessee - Knoxville
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Setup of one of the first tests of using polarized 3He on neutorn scattering instrument: POSY 1 neutron reflectometer at the Intensed Pulsed Neutron Source, Argonne National Laboratory.
This setup came from Mike Snow’s group at the Indiana University Cyclotron Facility.
Polarized 3He neutron spin filter
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SNS Instruments that can benefit from polarized 3He polarizer/analyzer
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HFIR Instruments that can benefit from polarized 3He polarizer/analyzer
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The development focuses at Oak Ridge
What we started with: Built & tested in-situ polarizer/analyzer with the 3He polarized on beam.
Now it gets a bit more exciting: Developing a medium-capacity laboratory-based SEOP-based filling station to supply several instruments.
And the fun continues (Tony): Compact instrument-based filling station that is located at the instrument and will automatically refill wide-angle analyzer with high-polarization gas every few hours.
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In-situ spin-filter with stable polarization and spin-state switching
*
Laser & optics
Polarized 3He Neutron Spin Filter
Detector
Sample (CoFe Analyzer)
Unpolarized Neutrons
Polarized Neutrons
We worked with the polarized 3He community (Hamilton, NIST, LENS) to develop the use of polarized 3He in neutron scattering. Some highlights:
• Put polarized neutrons on a pulsed source scattering instrument – Single Crystal Diffractometer, IPNS;• Online continuous polarizing to maintain the highest polarization that is stable for days during experiment;• Adiabatic-Fast-Passage technique to flip the 3He polarization to make a spin filter-flipper.G.L. Jones, et. al., Physica B 356, 86-90 (2005).G.L. Jones, et. al., Proceedings of ICANS-XVII, Vol. III, 838-843 (2006).
1 flip /10 min 1 filp/2 min
3He polarization = 67%
Wavelength (A)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Poa
lriz
atio
n P
, T
ransm
issi
on T
, F
OM
P2 T(T
ransm
issi
on o
f an u
npola
rize
d b
eam
)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Neutron Polarization
Transmission(Unpolarized incident beam)
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Using spin+/spin- polarized neutrons produced by the polarized 3He polarizer, we measured many magnetic peaks. Maximum entropy magnetization density reconstruction shows possible presence of a magnetic moment on the Sb site with opposite sign with respect to the Mn moment.
Sample magnet refrigerator
Polarized
Neutrons
Co Fe Analyzer to verify beam polarization
h,k,l I(+) I(-) I(+)/I(-) lambda (A)
10,0,0 721 89.49 8.06 2.539
9,2,-1 108 45.4 2.38 3.181
9,3,2 140 13.21 10.60 3.167
Spin + Spin -
10,0,0
9,3,2
9,2,1_ 10,0,0
9,3,2
9,2,1_
Experiment at SCD, IPNS: Magnetic moments on Mn & Sb in Yb14MnSb11
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Laser opticsCoils & Shield
Oven
3HeNeutron Beam
• Operates at neutron wavelengths from 1.8 Å to 6 Å• Cell ID~12 cm to accommodate off-specular scattering.• Online continuous optical pumping during experiment to
maximize and maintain a stable 3He polarization. • To use it with sample magnet, the analyzer is in a uniform
holding field enclosed in -metal magnetic shielding. • Use adiabatic-fast-passage for both NMR polarization
monitoring and 3He polarization flipping. This will enable the system to analyze spin-up and spin-down neutrons with fast-switching from one mode to the other.
• The system is located inside a laser-shielding housing. All operations will occur online.
• A total of 4 cells were made by Wang Chun Chen and Tom Gentile at NIST.
• 3He gas pressure = 1.52 - 1.92 bars at R.T.• Cell ID ~ 12 cm , cell length ~ 8 cm
3He analyzer for Magnetism Reflectometer
Wavelength (A)
0 1 2 3 4 5 6
Ana
lyzi
ng E
ffic
ienc
y P
, T
rans
mis
sion
T
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Analyzing efficiency P
TN (unpolarized neutrons)
T+ (spin +)
T- (spin -)
BL4A Reflectometer In-situ Analyzer3He polarization = 76%Cell pressure=1.52 bar, cell length=8 cmOperating wavelength= 2 - 5 AEmpty cell transmission=0.83
T0 (depolarized cell)
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3He analyzer for the SNS Magnetism Reflectometer 73% polarization reached
The system was installed and the on-beam tests were being done. • Neutron measurements showed 73% 3He polarization reached. • NMR measurement of the pump-up time constant ~ 5 hours. • Adiabatic fast passage worked to flip the 3He polarization.
Loss/flip<0.03%.• T1=315 hours at R.T.• In a previous test, we measured the 4 spin-dependent cross-
sections of off-specular scattering at lower 3He polarization.
Next steps:• Make new cell with larger opacity to match the BL4A setup. • Side-pumping setup
Wavelength (A)
0 1 2 3 4 5 6P
olar
izat
ion
P, T
rans
mis
sion
T
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Analyzing efficiency P
TN (unpolarized neutrons)
T+ (spin +)
T- (spin -)
BL4A Reflectometer In-situ Analyzer3He polarization = 73%Cell pressure=1.52 bar, cell length=8 cmOperating wavelength= 2 - 5 AEmpty cell transmission=0.83
T0 (depolarized cell)
Pump-up time constant=4.97 hours
Time (Hour)
0 5 10 15 20 25 30
3 He
Pol
ariz
atio
n
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8Relaxation: T1=315 hours
0.690
0.672
0.654
0.636
0.618
0.600
0.582
3H
e P
olar
izat
ion
0 10 20 30 40Time (Hour)
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Test: Reflectivity and Off-Specular Scattering
[57Fe/Cr]x12/Al2O3 multilayer with an anti-ferromagnetic
inter-layer coupling and with an in-plane magnetic domain structure. The polarized neutron reflection experiment was performed in an external magnetic field of 30 mT applied along the in-plane easy axis (001) after a saturation field of 0.5 Tesla. The 2D pattern of specular reflection and off-specular scattering was measured with polarized neutrons in the wavelength band 2 Å< <4.75 Å and a polarization of 0.97. The polarization analysis measurement was performed at 2 incident angles in order to obtain the range of momentum transfer Qz from 0.008 to 0.06 Å-1.
Off-Specular
Specular f=i
Off-Specular
Horizon
Incident
Illustration of the specular and off-specular scattering
fi
f
f
Time-Of-Flight
Time-Of-Flight
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Test of Non-Inductive Electric Heater to Heat a Cell
AFP: Fractional 3He polarization loss per flipHeater ON: 0.061% +/- 0.002%Heater OFF: 0.055% +/- 0.002%
Time (Hour)
0 10 20 30 40 50 60
NM
R F
ID A
mpl
itude
(A
rb. U
nit)
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0Heater OFF, T1=77.4 +/- 0.5 hoursHeater ON, T1=71.1 +/- 0.8 hours Electrical Heating:
Conventionally, hot air oven is used in SEOP. Flowing >200ºC hot air through a system, however, presents a host of technical and safety problems.Alternatively, we can use electric heaters. The main concerns are the magnetic interference on 3He polarization and on using adiabatic fast passage method to flip the 3He polarization and heating uniformity. Our tests showed none of them are a problem.
Pump-up time constant=33.1+/- 0.8 hours
Highest T1 tested on cell ~ 90 hours
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High-Power Bandwidth-Narrowed Laser
nLight @ 95 amp
Wavelength (nm)790 792 794 796 798 800
Inte
nsity
(arb
. uni
t)
0
500
1000
1500
2000
2500
3000
BroadbandNarrowedRb absorption
Modified Littrow cavity
A polarizing beam splitter cube separates the feedback and output beams, reducing the heating of the grating and allowing better optical arrangement for the feedback.
Laser Stack with volume Bragg grating (LaserTel)
Volume Bragg grating feedback narrows the bandwidth to 0.5-0.7 nm FWHM.
We just received and tested a 150 W 3-bar stack that centered on 794.7 nm (Rb D1). It shows ~ 1.7 x the performance obtain from narrowing a 100 W laser using Littrow external cavity (running at 75 W with 25 W feedback).
High power lasers tuned to 770.1 nm (K D1) has arrived last week.
Wavelength (nm)
790 791 792 793 794 795 796 797 798 799 800
La
ser
po
we
r d
en
sity
(W
/nm
)
0
50
100
150
200
250
300
LaserTel 3 x 50 W stack narrowed by Volume Bragg GratingOutput=150W (actual)NLight 75 W narrowed by Modified Littrow cavity. Output=50 W (actual)Estimated NLight 2 x 75 W narrowed by modified Littrow cavity
Commercial system using laser stack with external cavity
(XeMed)
12-to-24-bar system from XeMed
24-bar: 1000 W; 12-bar: 500 W
0.4 nm-width
2x1mrad divergence
140x140mm beam cross-section
Turn-key system with chillers, power supplies, safety interlocks and User Interface
Polarizing Beam Splitter Cube
Laser
3He cell
Reflection Grating
Magnetic field
4
2
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Lab-based SEOP Filling Station (More details in Tony’s Talk)
4.3 bar-liter optical-pumping cell• Material: GE180• ID 84 mm x 130 mm (nominal) • 6 mm thick wall = 12 bar limit• T=300ºC, maximum 6 bar at RT Production rate for this cell• Assume a relaxed 8-hour cycle• Prod. rate = 13 bar-liter/day
Status: • 2 cells made.
Gas-supply system• 15-bar gas pressure• Supply gas to
polarizing system while preparing 2 sealed cells.
• Status: Working. Filled second cell. Automatic gas pressure control accurate to +/-1 torr.
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talk
Hese
sealHe
HeseeXalk
alkPP ).][( )1
)1.]([
.][
Spin-exchange rate = kse [al.]
kse,K = 5.5×10-20 cm3 s-1
kse,Rb = 6.76×10-20 cm3 s-1
T (oC)150 200 250 300 350
Alk
ali
De
nsi
ty (
cm-3
)1013
1014
1015
1016
1017
[K]
[Rb]
Alkali Density [cm-3]
1013 1014 1015 1016
T95
[hou
rs]
100
101
102
103
K
Rb
TTK4453
408.916 10)/1025.7(][
TTRb4040
318.916 10)/1025.7(][
To increase the spin-exchange rate, we need to increase the alkali density [al.]
… by increasing the temperature
Example: Compare to the spin-exchange rate of a Potassium-based cell at 225ºC (1.5 day to reach 95% of equilibrium), the spin-exchange rate has a 10 x increase at 292ºC (4 hours) and 20 x increase (2 hours) at 316ºC due to the increase in alkali density.
Fast Pump-Up – Temperature Requirement
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Fast Pump-Up – Laser Power Requirement
drrop )(),()(
SDop
opalP
][])[(.][ 23
2NkHekkalk NalHelalsealSD
The spin-destruction comes from collision between polarized alkali atoms with other alkalis, nitrogen, and 3He
Temperature (oC)
150 200 250 300 350
SD
(s-1)
100
101
102
103
104
K
Rb
K-K
K-He
K-N2
The optical pumping rateopt ~ (v0)(v0) is typically 400 s-1 per mW/cm2
A 10 bar 3He, 50 torr N2 , 5cm
diameter cell will absorb 52 W at 292ºC , 100 W at 316ºC
Need:200-400W at 292ºC, 400-1kW at 316ºC.
= the light density, () = optical absorption cross-sectionPhoton efficiency ~ 10%
Example: Raising the temperature from 225ºC to 292ºC increases the spin-destruction rate by 6 x; and at 316ºC by 11 x.
Temperature (oC)
150 200 250 300 350
Ab
sorb
ed
po
we
r (W
att)
0
100
200
300
400
K
Rb
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Electron Paramagnetic Resonance Frequency Shift(Gordon Jones, Valarie Hanson, Xin Tong)
When placed in a magnetic field the electron spin states of an atom split with an energy difference proportional to that field. In optical pumping experiments pump light polarizes the alkali by exciting only the electrons in e.g. the 5S-1/2 state, such that eventually there becomes a net surplus in the 5S+1/2 state, indicating the gas is essentially polarized. When incoming photons are driven at the Zeeman frequency corresponding to the splitting due to the magnetic field, electrons in the 5S+1/2 state are recycled back to the 5S-1/2 state.This creates an increase in fluorescence emitted from excited electrons decaying down to ground state, as well as an increase in pump laser absorption.By locating the frequency where the fluorescence is maximized, the Zeeman splitting of the two states can be determined precisely. In the vicinity of polarized 3He, the B-field produced by the 3He shifted the Zeeman splitting frequencies. Measuring this shift gives us the absorb 3He polarization.
Static magnetic field
Laser
V
Photodiode
Cell of Rb, 3He, N2
V
We tested EPR-shift to measure the absorb 3He polarization.
Test setup: 50% polarization
RF field
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Faraday Rotation (Valarie Hanson, Xin Tong)
We tested Faraday rotation to measure the alkali density.
Probe Laser
Beam Splitter
Photodiode
Pho
todi
ode
• Assuming 100% rubidium polarization we could then calculate the density.
• We measured the λ/2 angle change when reversing the pump laser from σ+ to σ-.
[Rb] at 165˚C = 1.76x1014 cm-3
[Rb] at 175˚C = 2.77x1014 cm-3
Calculated Densities Based on Temperature
Experimentally Derived Densities[Rb] at 165˚C = 1.78x1014
cm-3
[Rb] at 175˚C = 3.18x1014 cm-3
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ORNL
Valeria Lauter (Mag. Refl.)
Hailemariam Ambaye
Andre Parizzi
Rick Goyette
Kevin Shaw
Mark Hagen (HYSPEC)
Bill Leonhardt
David Anderson
Bryan Chakoumakos (HB3A SCD)
Kenneth Litttrell (CG2 GPSANS)
Christina Hoffmann (TOPAZ)
Jack Thomison
Mark Lumsden (HB3 triple-axis)
Hamilton College
Gordon L. Jones
Valerie Hanson
Freddie Dias
Brian Collett
Jonathan Wexler
NIST Tom GentileWangChun ChenChangbo Fu
IPNS Paula M. B. PiccoliMartha E. MillerArt SchultzSuzanne te Vultuis
IUCF Indiana Univ. Helmut KaiserDavid BaxterChristopher LavelleW. Mike SnowHai Yan YanPeter Chenyang Jiang
ILL
Ken Andersen
Eddy Lelievre-Berna
David Jullien
Pascal Mouveau
Alexander Petukove
ISIS
Steve Parnell
Stephen Boag
Chris Frost
Univ. of New Hampshire Bill Hersman
Acknowledgement
JCNS-FRM-2 Earl Babcock
ANSTOFrank Klose