Polarized 3He Filling Stations

1
Polarized 3He Filling Stations

• Xin Tong (Tony)
• Instrument Development Group
• Neutron Facilities Development Division
• Oak Ridge National Laboratory
• Oak Ridge, TN 37831, USA

2
Polarized 3He Neutron Analyzer
Polarized 3He neutron spin filter is based on the
spin-dependence of the neutron absorption of 3He.
If the 3He nuclear spin and the neutron spin are
anti-parallel, the absorption is very strong sa
(??) 5931 b for l1 Å neutrons. If the spins
are parallel, there is virtually no absorption.
sa (??) 0. The absorption cross-section is
proportional to the neutron wavelength l.
Laser optics
3He NSF
Neutrons
Cell Barbara 3He polarization PHe 73 Pressure
1.52bar ø11.7 cm ID, l 8.1 cm Pump up time
constant 5 hrs
3
Why 3He Filling Station

• The need to change 3He pressure throughout an
  experiment
• For neutron scattering experiments off different
  neutron wavelengths, the optimized 3He pressure
  is different.
• The two conventional way of using 3He in
  polarized neutron scattering does not involve
  changing of 3He pressure / 3He cell.
• Polarized 3He for instruments with limited space
  which can not accommodate an in-situ SEOP pumping
  system
• Space for laser, optics, solenoids, etc.
• Solution for cells with difficult shape (HYSPEC
  wide angle analyzer)
• Conventional cylindrical 3He cell is easily
  pumped and preserves a long 3He relaxation time
• With current optical pumping technology, it is
  not easy to pump an irregular cell.

4
3He Filling Stations at Oak Ridge

• Instrument based 3He filling station with
  Spin-exchange optical pumping
• Compact system which will be installed onto an
  SNS beamline Hybrid Spectrometer (HYSPEC)
• Its subsystems include a 3He gas filling station,
  a 3He polarizing system a gas transfer system and
  a gas recycle system
• Lab based 3He filling station
• A sophisticated system with three gas lines
• Ability to fill up to three different 3He cells
  at the same time
• Able to create sealed 3He cells for in-situ 3He
  pumping based on experiment requirements

5
HYSPEC (Hybrid Spectrometer) Wide-Angle Analyzer

• Should cover the 60 degree horizontal range of
  the detector bank
• Should cover as much as is possible of the 7.5
  degree vertical range of the detector bank
• Should allow an exclusion zone at the sample
  position of diameter 150mm

Optical pumping is difficult due to the limited
space in the instrument and the shape of the
cell. Refilling in-situ with a on-site compact
filling station is the solution we are going for.
6
HYSPEC 3He Filling Station Design
Gas return
SEOP based polarized 3He filling station
3He cell
Polarize
Sample
Polarized gas transfer local filling
Gas supply
Uniform field coil
Example Max. 3He polar. 72, optimized at 90
meV. T1100 hours, exchange all the gas every 5
hours. (Plot for 50 meV neutrons)
7
Optics
Shielding
Laser
Breadboard
Pressure Gauge
Gas Supply
Getter
Power Supply
Amplifier
Rough Pump
Turbo Pump
Function Generator
Laser Power Supplies
8
HYSPEC 3He Filling Station Features

• Three-level compact station
• Gas filling level
• Optical pumping level
• Pumps / Electronics level
• Potassium instead of Rubidium for fast pumping
  process
• Fully electronically control

9
Compact Filling Station Schemes Next Steps

• Customize magnetic shielding and oven
• Test polarized gas transfer components
• Test valved Potassium-based cell for high
  temperature operation
• Instrument Development Test beam lines available
  beginning in June for testing.

10
Lab-based 3He Filling Station

• Gas-supply system
• 15-bar gas pressure
• Supply gas to polarizing system while preparing 2
  sealed cells.
• Status Baking the system. Ready to fill a cell.

11
Lab-based 3He Filling Station Optical Pumping
Cell

• 4 bar-liter optical-pumping cell
• Material GE180
• ID 84 mm x 130 mm (nominal)
• 6 mm thick wall 12 bar limit
• T300ºC, maximum 6 bar at RT
• Production rate for this cell
• Assume a relaxed 8-hour cycle
• Prod. rate 15 bar-liter/day
• Status
• 2 cells made. Install gas-polarizing system for
  polarized gas production soon.

12
Summary

• Compact filling station
• In progress
• HYSPEC beam commission 2010
• Lab-based filling station
• Cells made, prepare to fill
• Test and commission soon

13
Acknowledgement
Wai Tung Hal Lee Dennis Rich Mike Fleenor Akbar
Ismaili Lee Robertson Mark Hagen (HYSPEC) Bill
Leonhardt David Anderson
Tom Gentile (NIST) Wangchun Chen Changbo
Fu Gondon Jones (Hamilton)