Oak Ridge Lab’s SEOP R&D Efforts

Managed by UT-Battellefor the Department of Energy

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


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


SNS Instruments that can benefit from polarized 3He polarizer/analyzer


HFIR Instruments that can benefit from polarized 3He polarizer/analyzer


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.


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)


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


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)


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)


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


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


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


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.


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


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


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


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


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

Oak Ridge Lab’s SEOP R&D Efforts

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