Using polarized 3He spin filter at the SNS

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Using polarized 3He spin filter at the SNS
- Update on current development
W.T. Hal Lee Spallation Neutron Source
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OUTLINE

• March 06 Experiment at SCD, IPNS
• 3He analyzer for use on the Magnetism
  Reflectometer
• A plausible setup on HYSPEC

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March 06 Experiment at SCD, IPNS Polarized
neutron diffraction study of the ferromagnetic
semiconductor Yb14MnSb11
V.O. Garlea1, G.L. Jones2, B. Collett2, W.C.
Chen3,5, T.R. Gentile3, P.M.B. Piccoli4, M.E.
Miller4, A.J. Schultz4, H.Y. Yan5, X. Tong5, M.
Snow5, B.C. Sales1, S.E. Nagler1, W.T. Lee6, C.
Hoffmann6 1HFIR, Oak Ridge National Laboratory,
Oak Ridge, TN 378312 Hamilton College, Clinton,
NY 13323 3 NIST Center for Neutron Research,
Gaithersburg, MD 20899 4 IPNS, Argonne National
Laboratory, Argonne, IL 60439 5 IUCF, Indiana
University, Bloomington, IN 47405 6 SNS, Oak
Ridge National Laboratory, Oak Ridge, TN 37831
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Previously

• In 2004, we tested online continuous optical
  pumping that kept the 3He polarization stable for
  days using a compact online system.
• In 2005, an improved setup optimized at the
  instrument resulted in close to the highest 3He
  polarization archived in a prior off-line test
  and remained stable for days.
• In 2005, we tested fast-switching of 3He
  polarization by adiabatic fast passage (AFP). We
  repeatedly switch between spin spin- neutron
  filtering modes without using a neutron spin
  flipper.

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Experiment setup at SCD, IPNS
2005
Detector
3He cell inside B-field AFP coil
Unpolarized Neutron
Polarized Neutron
Co Fe Analyzer
2006

Polarized Neutron
Polarizer (light)
Laser
Co Fe Analyzer
Sample magnet refrigurator
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Experiment setup at SCD, IPNS
Detectors
Neutrons
Sample magnet
Laser

• 3He polarization 60
• Online continuous optical pumping
• AFP 3He polarization switching
• Cold sample to 6K
• 3kG sample field

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Snap shot of the scattering experiment
The experiment Measure magnetic moments on Mn
Sb
Spin
Spin -
Many of the peaks are magnetic Data analysis is
underway
We have made the transition from developing a 3He
polarizer to carrying out polarized neutron
scattering measurements.
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Construction of a 3He-based neutron polarization
analyzer for use at the Magnetism Reflectometer
W. T. Hal Lee, SNS T. Gentile, W.C. Chan, NIST G.
L. Jones, Hamilton College
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3He analyzer for Magnetism Reflectometer

• Operates at neutron wavelengths from 1.8 Å to 6 Å
• Online continuous optical pumping during
  experiment to maximize and maintain a
  non-decaying 3He polarization.
• The analyzer cell is in a uniform holding field
  enclosed in m-metal magnetic shielding to
  mitigate external magnetic interference.
• Use adiabatic-fast-passage for both NMR
  polarization monitoring and 3He polarization
  flipping. This will enable the system to analyze
  spin-up and spin-down neutrons with
  fast-switching from one mode to the other.
• The system is located inside the detector
  housing. All operations will occur online

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3He analyzer for Magnetism Reflectometer
Chianti Max 3He polarization74.5 for 53 W of
narrowed lightT1270 h Pressure 1.82 bar 11.7
cm ID, 8.1 cm inside length12.9 cm OD, 10 cm
outside length, 4 cm tip-off length
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3He analyzer for Magnetism Reflectometer
Grating
Output to 3He cell
Laser
Beam Split
At 60 W, with 20 W feedback and 40 W output, At
794.7 nm, Narrowed peak intensity 2.25 x total
un-narrowed peak intensity
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Individual components tested. Polarizing 3He
test in April
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A plausible scheme for 3He-based neutron
polarization analyzer for HYSPEC
W. T. Hal Lee, SNS M. Hagen, SNS L. Passell, BNL
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3He analyzer for HYSPEC
Gas return
Local filling
A SEOP based filling station
Polarizing
Sample
Polarized gas supply
3He cell
Coil
Optical pumping may be difficult due to the shape
of the cell. Refilling may be the solution.
Filling station example
Max 3He polar. 0.75, optimized at 1.5 Å. T1200
hours, refill 75 volume every 5 hours. (Plot
for 2 Å neutrons)
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HYSPEC
2 pairs of coils with diameter 400 mm 350 mm
separated by 400 mm. By applying appropriate
currents to the coils, field uniformity similar
to a pair of 400 mm diameter Helmholtz coils can
be obtained.
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SNS Instrument Layout
2 - Backscattering Spectrometer
Field Sensitive
3He filter, magnet
magnet
1A Vacant
17 - SEQUOA
18 - ARCS
1B - NOMAD
16 Vacant
SERGIS
3 - SNAP
14A, 14B, 15
SESANS
HYSPEC
NSE
4A - Magnetism Refl.
m-SANS
13 - Fundamental Physics
4B - Liquids Refl.
Mandi
5 - CNCS
Vision
New concept
6 - SANS
12 - SCD
7 Vacant
11B Vacant
8 Vacant
11A POWGEN3
9 - VULCAN
10 Vacant
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Self-shielded split-pair 10 Tesla superconducting
magnet study - Results

• Substantial reduction of fringe field in both
  radial and axial directions
• Shielding factor 40-50