# Presentation: 187718

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

*University of Tennessee*

- EDM Collaboration meeting
- June 20-21, 2005

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

- The SNS FNPB and 8.9-A Neutrons

## SNS FNPB

- Guide size = 12cm x 14cm
- @ Monochromator exit

- Length of 8.9Å line ~ 33 m

- Takeyasu Ito

## Original FNBP Baseline

- 12cmx14cm m=3.5 straight guide

- But, there are a few issues......

- Takeyasu Ito

## Finite reflectivity at m>1

* ****c*=1.56x10-2 rad for 8.9Å
- In a 12 cm wide guide, m=3.5 neutrons bounce off the wall every 2.2 m.

- Takeyasu Ito

## Matching with EDM polarizer/splitter

- 10.16 cm

- 7.62 cm

- ?

- 25.4 cm

- 12 cm

- Takeyasu Ito

## Ballistic guide

- Low m

- High m

- Takeyasu Ito

## McStas Simulation Results

- L1

- L2

- L1

- 30 cm in x
- 32 cm in y

- 14 cm in x
- 16 cm in y

- Straight guide (14 cm x 16 cm)                 1.00(2)x109 n/s/Å
- L1/L2/m1/m2=5m/23m/3.6/2                     1.43(2)x109 n/s/Å
- L1/L2/m1/m2=7m/23m/3.6/2                     1.43(2)x109 n/s/Å
- L1/L2/m1/m2=9m/23m/3.6/2                     1.47(2)x109 n/s/Å

- Takeyasu Ito

## 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.

- Takeyasu Ito

## EDM Neutron Polarizer/ Splitter

- Takeyasu Ito

## Polarizer/splitter simulation

- _Splitter/Polarizer Model Top View _

- Starting values:
- XW1=12cm; XW2=30cm; XW3=15cm; XWA=5.08cm; XW4=7.62cm
- L1=9m; L2=10m; L3=11m; L4=3m; Ldet=70cm
- mHorn=3.5, mStraight=1.5; mPolarizer=2.4; m=3.5 for the rest

- Takeyasu Ito

## Polarizer/splitter simulation

- _Splitter/Polarizer Model Side View _

- Starting values:
- YW1=14cm; YW2=30cm; YW3=14.41cm; YW4=10.16cm

- Takeyasu Ito

## Effect of the Diverging Horn

- Initial angular distribution: uniform from -3.5 to 3.5
- [Counts in (-1.5<m<1.5)]/[Total generated] = 80 %

- Angular distribution in X after the 9m horn

- Takeyasu Ito

## Some results

- Initial neutron distribution
- Uniform: -6cm<x<6cm, -7cm<y<7cm, -3.5<m<3.5 (in both x and y)
- 12cmx14cm, m=3.5 straight guide
- Transmission=36%
- Ballistic guide (L1=9m,L2=15m,m1=3.5,m2=2.0)
- Transmission=69%
- Polarizer/Splitter
- Transmission to the end of the guide=43%
- Transmission to the cell=25%
- Polarization=94%
- FNPB ballistic guide consistent with EDM needs

- Takeyasu Ito

## Polarizer/splitter simulation

- _Splitter/Polarizer Model Top View _

- Starting values:
- XW1=12cm; XW2=30cm; XW3=15cm; XWA=5.08cm; XW4=7.62cm
- L1=9m; L2=10m; L3=11m; L4=3m; Ldet=70cm
- mHorn=3.5, mStraight=1.5; mPolarizer=2.4; m=3.5 for the rest

- Takeyasu Ito

## 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?

- Takeyasu Ito