Polarized 3He Neutron Spin Filter Development at ORNL

Hal Lee, Dennis Rich

Instrument Development Group,

Neutron Facilities Development Division

Oak Ridge National Laboratory

Oak Ridge, TN 37831, USA

What we have done in the past

• Together with Hamilton College (Gordon Jones), NIST, and IUCF, we developed some useful techniques to use SEOP type polarized 3He neutron spin filter– On-beam continuous optical pumping to keep the polarization stable

– Use adiabatic fast passage to flip the 3He polarization.

– Carry out experiments using a roll-on/roll-off polarizer on the Single Crystal Diffractometer at the Intense Pulsed Neutron source, Argonne National Laboratory.

• We developed a polarized 3He analyzer for use on the Magnetism Reflectometer, Spallation Neutron Source– Covers 10” diameter cross-section area.

– On-beam optical pumping

– AFP flipping of the 3He polarization

– Cell made by NIST tested in laboratory to reach 74.5% 3He polarization

– Test at HFIR planned for November. Test on line planned for January (laser safety delay).

Polarizer with online pumping and AFP flipping

*

Laser & optics

Polarized 3He Neutron Spin Filter

Detector

Sample (CoFe Analyzer)

Unpolarized Neutrons

Polarized Neutrons

We have been working with the polarized 3He community (Hamilton, NIST, LENS) to develop the use of polarized 3He in neutron scattering. Some highlights:

• used polarized neutrons on a pulsed source scattering instrument beyond reflectometer - SCD, IPNS;

• used online continuous optical pumping to maintain a stable polarization in scattering experiment;

• tested using AFP 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).

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

Poalriz

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

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1.0

Neutron Polarization

Transmission(Unpolarized incident beam)

1 flip /10 min 1 filp/2 min

What we have done in the past

• Together with Hamilton College (Gordon Jones), NIST, and IUCF, we developed some useful techniques to use SEOP type polarized 3He neutron spin filter– On-beam continuous optical pumping to keep the polarization stable

– Use adiabatic fast passage to flip the 3He polarization.

– Carry out experiments using a roll-on/roll-off polarizer on the Single Crystal Diffractometer at the Intense Pulsed Neutron source, Argonne National Laboratory.

• We developed a polarized 3He analyzer for use on the Magnetism Reflectometer, Spallation Neutron Source– Covers 10” diameter cross-section area.

– On-beam optical pumping

– AFP flipping of the 3He polarization

– Cell made by NIST tested in laboratory to reach 74.5% 3He polarization

– Test at HFIR planned for November. Test on line planned for January (laser safety delay).

Polarized 3He based analyzer for Magnetism Reflectometer

Laser optics

Neutrons

3He neutron spin filter

Cell Chianti3He polarization PHe = 74.5%

Pressure = 1.82 bar (n=4.46 x 1019 cm-3)

ø11.7 cm ID, l = 8.1 cm 1-2 days to polarized to 74.5%

3He Pol = 23%after 18 hours pumping at 170oC

Wavelength (A)

0 1 2 3 4 5 6 7

Tra

nsm

issi

on

0.01

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1.00

Test at Indiana Univeristy Cyclotron Facility

We only polarized the cell at 170ºC for 18 hours, the 3He polarization reached 23%. The result is consistent with the test at NIST where the cell was polarized at 200ºC for 2-3 days.

What we are doing now

• 3He Filling Station Development:

We are constructing a filling station that can– Prepare 2 sealed cells simultaneously– Fill an additional valved optical pumping cell for R&D and polarized 3He gas

production.

• Wide-angle analyzer (ORNL): – Our glass shop has made a prototype wide angle quartz cell. – ID=6”/150mm, OD=12”/300mm, Arc=45º, H=3”/75mm, Wall=3-5 mm. – The cell is being prepared for testing at ILL.

• Additional information - Wide-angle analyzer (NIST): – NIST purchased a quartz cell: ID=140 mm, OD=300mm, Arc=120º, H=80mm,

Wall=3/16”/5mm.– The cell was filled as a hybrid sealed cell for direct optical pumping– The cell turns an amber color at 220ºC

• Laser Optics: – In the past, we modified the Littrow cavity for high-power laser. – We will be testing laser stack narrowed by volume Bragg grating.

To dry pump

3He

4He

RegulatorGetter

Baratron

N2

Regulator

Baratron

Regulator

Baratron

Getter

Getter

To turbo pump

Gas lines - simplified schematic

3He Filling Station

To dry pump

3He

4He

RegulatorGetter

Baratron

N2

Regulator

Baratron

Regulator

Baratron

Getter

Getter

To turbo pump

System bake out

To dry pump

3He

4He

RegulatorGetter

Baratron

N2

Regulator

Baratron

Regulator

Baratron

Getter

Getter

To turbo pump

Cell bake out

To dry pump

3He

4He

RegulatorGetter

Baratron

N2

Regulator

Baratron

Regulator

Baratron

Getter

Getter

To turbo pump

Cell bake out

To dry pump

3He

4He

RegulatorGetter

Baratron

N2

Regulator

Baratron

Regulator

Baratron

Getter

Getter

To turbo pump

Fill Cell – Fill Nitrogen

To dry pump

3He

4He

RegulatorGetter

Baratron

N2

Regulator

Baratron

Regulator

Baratron

Getter

Getter

To turbo pump

Fill Cell – Empty excess Nitrogen

To dry pump

3He

4He

RegulatorGetter

Baratron

N2

Regulator

Baratron

Regulator

Baratron

Getter

Getter

To turbo pump

Fill Cell – Fill Helium-3

To dry pump

3He

4He

RegulatorGetter

Baratron

N2

Regulator

Baratron

Regulator

Baratron

Getter

Getter

To turbo pump

Fill Cell – Empty excess Helium-3

To dry pump

3He

4He

RegulatorGetter

Baratron

N2

Regulator

Baratron

Regulator

Baratron

Getter

Getter

To turbo pump

Fill Cell – Fill Helium-4

To dry pump

3He

4He

RegulatorGetter

Baratron

N2

Regulator

Baratron

Regulator

Baratron

Getter

Getter

To turbo pump

Fill Cell – Empty Excess Helium-4

To dry pump

3He

4He

RegulatorGetter

Baratron

N2

Regulator

Baratron

Regulator

Baratron

Getter

Getter

To turbo pump

Fill Cell – Fill One, Bake the other

3He Filling Station

What we are doing now

• 3He Filling Station Development:

We are constructing a filling station that can– Prepare 2 sealed cells simultaneously– Fill an additional valved optical pumping cell for R&D and polarized 3He gas

production.

• Wide-angle analyzer (ORNL): – Our glass shop has made a prototype wide angle quartz cell. – ID=6”/150mm, OD=12”/300mm, Arc=45º, H=3”/75mm, Wall=3-5 mm. – The cell is being prepared for testing at ILL.

• Additional information - Wide-angle analyzer (NIST): – NIST purchased a quartz cell: ID=140 mm, OD=300mm, Arc=120º, H=80mm,

Wall=3/16”/5mm.– The cell was filled as a hybrid sealed cell for direct optical pumping– The cell turns an amber color at 220ºC

• Laser Optics: – In the past, we modified the Littrow cavity for high-power laser. – We will be testing laser stack narrowed by volume Bragg grating.

Wide Angle Analyzer Cell – ORNL, NIST

Our first test cell. To be Cs coated, filled, and tested at ILL.

No stress point found under polarized light

NIST attempt to directly pump the wide-angle cell:

Potassium reacts with quartz glass at >200ºC?

Preliminary test shows the passage of 794.7 nm light is not affected by the coloring.

What we are doing now

• 3He Filling Station Development:

We are constructing a filling station that can– Prepare 2 sealed cells simultaneously– Fill an additional valved optical pumping cell for R&D and polarized 3He gas

production.

• Wide-angle analyzer (ORNL): – Our glass shop has made a prototype wide angle quartz cell. – ID=6”/150mm, OD=12”/300mm, Arc=45º, H=3”/75mm, Wall=3-5 mm. – The cell is being prepared for testing at ILL.

• Additional information - Wide-angle analyzer (NIST): – NIST purchased a quartz cell: ID=140 mm, OD=300mm, Arc=120º, H=80mm,

Wall=3/16”/5mm.– The cell was filled as a hybrid sealed cell for direct optical pumping– The cell turns an amber color at 220ºC

• Laser Optics: – In the past, we modified the Littrow cavity for high-power laser. – We will be testing laser stack narrowed by volume Bragg grating.

Laser optics

Laser

3He cell

Reflection Grating

2

Magnetic field

4

Polarizing Beam Splitter Cube

nLight @ 95 amp

Wavelength (nm)790 792 794 796 798 800

Inte

nsity

(arb

. uni

t)

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BroadbandNarrowedRb absorption

Modified Littrow cavity

(Hal Lee, manuscript to Journal of Applied Physics)

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Current (Amps)

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Power Voltage

Laser Stack with volume Bragg grating

Volume Bragg grating feedback narrows the bandwidth to 0.5 nm FWHM.

We purchased a 150W 794.7 nm stack from LaserTel.

An example below: 780 nm, 500 W, 0.5 nm FWHM laser stack from LaserTel (60 amp, 18 V, 50% efficiency).

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Wavelength (nm)

Inte

nsit

y

ORNL

Mark Hagen

Bill Leonhardt

Christina Hoffmann

Jack Thomison

Hamilton College

Gordon L. Jones

Freddie Dias

Brian Collett

Jonathan Wexler

NIST Tom GentileWang Chun Chen

ANL Paula M. B. PiccoliMartha E. MillerArt Schultz

IUCF Indiana Univ. Hai Yan YanTony Xin TongPeter Chenyang JiangW. Mike Snow

ILL

Ken Andersen

Eddy Lelievre-Berna

David Jullien

Pascal Mouveau

Earl Babcock

ISIS

Steve Parnell

Steven Boag

Chris Frost

Univ. of New Hampshire Bill Hersman

Acknowledgement