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Polarized 3 He Filling Stations. Xin Tong (Tony) Instrument Development Group Neutron Facilities Development Division Oak Ridge National Laboratory Oak Ridge, TN 37831, USA. Polarized 3 He Neutron Analyzer.

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polarized 3 he filling stations

Polarized 3He Filling Stations

Xin Tong (Tony)

Instrument Development Group

Neutron Facilities Development Division

Oak Ridge National Laboratory

Oak Ridge, TN 37831, USA

slide2

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 l=1 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

why 3 he filling station
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.
3 he filling stations at oak ridge
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-situ3He pumping based on experiment requirements
slide5

No stress point seen under polarized light

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.

hyspec 3 he filling station design
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. T1=100 hours, exchange all the gas every 5 hours. (Plot: for 50 meV neutrons)

slide7

Optics

Shielding

Laser

Breadboard

Pressure Gauge

Gas Supply

Getter

Power Supply

Amplifier

Rough Pump

Turbo Pump

Function Generator

Laser Power Supplies

hyspec 3 he filling station features
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
compact filling station schemes next steps
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.
lab based 3 he filling station
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.
lab based 3 he filling station optical pumping cell
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
  • T=300ºC, 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.
summary
Summary
  • Compact filling station
    • In progress
    • HYSPEC beam commission 2010
  • Lab-based filling station
    • Cells made, prepare to fill
    • Test and commission soon
slide13

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)