SNS FNPB Status

1
The SNS FNPB and 8.9-A Neutrons

• Introduction
• SNS FNPB Status
• EDM beam polarizer/splitter simulation

Takeyasu Ito University of Tennessee
EDM Collaboration meeting June 20-21, 2005
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SNS FNPB
Guide size 12cm x 14cm _at_ Monochromator exit
Length of 8.9Å line 33 m
3
Original FNBP Baseline
12cmx14cm m3.5 straight guide
But, there are a few issues
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Finite reflectivity at mgt1

• qc1.56x10-2 rad for 8.9Å
• In a 12 cm wide guide, m3.5 neutrons bounce off
  the wall every 2.2 m.

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Matching with EDM polarizer/splitter
7.62 cm
12 cm
?
10.16 cm
25.4 cm
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Ballistic guide
Low m
High m
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McStas Simulation Results
14 cm in x 16 cm in y
30 cm in x 32 cm in y
L2
L1
L1

• Straight guide (14 cm x 16 cm)
  1.00(2)x109 n/s/Å
• L1/L2/m1/m25m/23m/3.6/2
  1.43(2)x109 n/s/Å
• L1/L2/m1/m27m/23m/3.6/2
  1.43(2)x109 n/s/Å
• L1/L2/m1/m29m/23m/3.6/2
  1.47(2)x109 n/s/Å

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New FNBP Baseline

• Present status
• Detailed simulation (P. Huffman) including curved
  guide
• Cost estimate from manufacture
• Currently in the procurement process.
• First 8 meters are to be purchased on FY05
  dollars.
• Remaining portion is to be an option that can be
  exercised in FY08.

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EDM Neutron Polarizer/ Splitter
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Polarizer/splitter simulation
Splitter/Polarizer Model Top View
Starting values XW112cm XW230cm XW315cm
XWA5.08cm XW47.62cm L19m L210m L311m
L43m Ldet70cm mHorn3.5, mStraight1.5
mPolarizer2.4 m3.5 for the rest
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Polarizer/splitter simulation
Splitter/Polarizer Model Side View
Starting values YW114cm YW230cm
YW314.41cm YW410.16cm
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Effect of the Diverging Horn
Angular distribution in X after the 9m horn
Initial angular distribution uniform from -3.5
to 3.5 Counts in (-1.5ltmlt1.5)/Total generated
80
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Some results

• Initial neutron distribution
• Uniform -6cmltxlt6cm, -7cmltylt7cm, -3.5ltmlt3.5 (in
  both x and y)
• 12cmx14cm, m3.5 straight guide
• Transmission36
• Ballistic guide (L19m,L215m,m13.5,m22.0)
• Transmission69
• Polarizer/Splitter
• Transmission to the end of the guide43
• Transmission to the cell25
• Polarization94
• FNPB ballistic guide consistent with EDM needs

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Polarizer/splitter simulation
Splitter/Polarizer Model Top View
Starting values XW112cm XW230cm XW315cm
XWA5.08cm XW47.62cm L19m L210m L311m
L43m Ldet70cm mHorn3.5, mStraight1.5
mPolarizer2.4 m3.5 for the rest
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Summary/Plans/Comments

• FNBP Baseline changed to accommodate the
  possibility of ballistic guide
• Polarizer/Splitter simulation under way
• Initial results 25 transmission from the
  monochromator to the cells 94 polarization
• FNPB ballistic guide design consistent with EDM
  needs
• Almost a factor two reduction in neutron flux
  from the end of the guide to the cell
• Neutron guide inside the cryostat?