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Polarized 3 He Filling Stations

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

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  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 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

  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-situ3He pumping based on experiment requirements

  5. 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.

  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. T1=100 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 • 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.

  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)

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