HERE’S THE SITU-ATION:

Optimizing and Testing a Prototype for Beamline Helium-3 

Polarization

Joelle Baer

(IN)
PRESENTATION OVERVIEW

What is 3He used for at the NIST Center for 

Neutron Research (NCNR) ?

What is the In Situ Polarizer?

What are the steps in designing and 

optimizing such a device?

Findings from neutron beam testing.
NIST CENTER FOR NEUTRON RESEARCH 250 days of 

operation per 

year

28 experiment 

stations for 

scientific research

Over 2000 users 

from university, 

government, 

institution and 

industry

Home to a 20 MW reactor that provides neutrons for scientific 

research
polarized 

outgoing 

neutrons

unpolarized

incoming 

neutrons

polarized 

3He

K.P. Coulter et al, NIM A 288, 463 (1990)

What is a 3He cell? 

Spin dependent 

neutron 

absorption
WHAT IS A 3HE 

CELL? 

• Back-filled with 

3He and a small 

amount of N2

• Combination of 

distilled Rb/K 

• Different cell 

characteristics

• Single unit for 

Analyzer and 

Flipper Cell for Typical Beam 

Experiments (Slider) Wide Angle Cell (Reliance)
WHAT IS POLARIZED 3HE USED FOR AT 

THE NCNR? 

INT 30 m SANS

40 m VSANS

DCS

PHYSICS

SPINS DIFF

MAGIK

CANDOR MACS BT-7

BT-1

Now

Future

www.ncnr.nist.gov/equipment/he3nsf
Cross Sections:

polarizer

flipper flipper

sample analyzer

detector

RF Sleeve RF Sleeve

• Probe magnetic 

properties from 

a sample

• Measure four 

cross sections

• Example

Polarization Analysis using 3He
Polarizing the Cell

Spin Exchange Optical Pumping (SEOP)

• Near infrared 

laser

• Electrons are 

polarized

• Spin exchange 

with 

3He

• Lengthy process
WHY DO WE NEED AN INSITU SYSTEM?
CREATING AN INSITU SYSTEM

• Compress ~7 foot 

long apparatus 

into under 4 

square feet of 

space

• Enclose the oven, 

RF coil and lasers 

in laser shielding

• Orient the 

equipment with 

both the laser and 

neutron beams

• Neutron beam 

and laser beam 

are orthogonal

• Allow access to 

the oven and 

lasers

System in early stages of configuration
LASER PUMPING SET UP

Laser

Chirped Volume 

Holographic grating (VHG)

Concave Cylindrical Lens

Mirrors

Quarter 

Wave 

Plates

Analyzer

X5 Magnification 

from two 

spherical lenses

Beamsplitter cube to ensure a perfectly 

linearly polarized laser light

• 100 W semiconductor single 

diode

• 795 nm wavelength with 2nm 

spectral linewidth

• Spectrally narrowed with 

Chirped VHG to 0.2nm 

spectral linewidth
DESIGNING THE LASER 

SHIELDING

• Necessary to prevent laser 

leakage 

• Panels made of Black 

Oxidized Aluminum

• Doors for access to laser 

box and oven sections
DESIGNING THE LASER 

SHIELDING
CONSTRUCTING 

THE LASER BOX

• Shielding crimped with Black 

Oxidized Al Edge trim

• Slide down the 80-20 extrusions

• Crimped with a punch and 

hammer

• Door covers bolt to the 80-20 

extrusion

• Preliminary tests- • Oven heating 

• Polarization flipping efficiencies
CONSTRUCTION DEVELOPMENT

• Design change for the walls of the box for ‘ease’ of construction

• Changing the compressed air tubing 3 times to optimize oven 

heating

• Replacing parts of the oven for better insulation

• Cutting and re-cutting the sides for various pass through notches 

(power, water, air)

• Not being able to get the system out of the lab hallway

• Having to create a cooling system because the box sealed too 

well that the lasers overheated

• Replaced a laser and 3 Silicone windows
TESTING AT PHADES 

Polarized Helium-3 And Detector Experiment Station
v

TESTING AT PHADES 

• Initial testing:

• Total neutron transmission

• Total Helium-3 polarization

• Total neutron polarization

• Cell Lifetime

• First Insitu polarizer to 

perform with comparable 

efficiency 

Neutron Polarization:

Pn = 

TT+−TT−

TT++TT−

= ttttttt (σ(λ)NNHHHHLPPHHHH)

Neutron Transmission:

TTnn = TT0cosh(σ(λ) NNHHHHLPPHHHH Pn )

Tn

Neutron Polarization & Transmission
NEXT STEPS

• Testing:

• Optimizing laser alignment

• Determining magnetic hotspots

• Future Models:

• Reconfigure Helmholtz coils to a vertical orientation

• Adding more lasers

• Adding sample environment capability 

• Manifold panel for quick disconnect

• Dedicated instrument cabling

• My Work with the Helium-3 team:

• Focus my senior thesis working with Gordon Jones on creating a gradiometer, a way to 

measure the field gradient in a polarized 3He cell using FID NMR 
Acknowledgements

Many thanks to 

The SURF Program, the NSF, Wangchun Chen, Shannon Watson, Robert Dimeo, Dan Neumann, Julie Borchers, Tom Gentile and Gordon Jones

Special Thanks to the Mechanical Engineering Technicians for quick turn around on machining
QUESTIONS?