Characteristics of Proposed Beamline(s) for Fundamental Physics Research at the SNS
Paul Koehler, Physics Division, ORNL
with help from:
John Ankner, Chris Gould, Geoff Greene, Erik Iverson, Jim Johnson, Frank Klose, Wei Lu, Seppo Penttila, Mike Snow, and
J.K. Zhao
Physical layout.
Simulations of fluxes, etc.
Choppers.
Important Questions.
Instrument Hall at the SNS
� Beam lines 13, 14 and 15 on bottom downstream moderator.
Coupled H2.
� Beam line 14 has �dual� shutter.Similar to beam lines (4A&B) for reflectometers.
Beam Line 14
SNS Moderators and Shutters
� Four Moderators.2 Coupled H2 � Top Downstream - beam lines 4, 5, and 6.
Bottom Downstream � beam lines 13, 14,and 15.
1 Decoupled H2.1 Ambient H2O.
15 14 13
Reflectometers
Moderators
Best Available Beamlines for Fundamental Physics
More Shutter Details
� Possible to extend guide to within 1 m of moderator by installing in core vessel insert.
Access and alignment may be difficult.Radiation damage too high for guides?What is impact of starting guide at shutter (2.2 m fromsource)?
Cutaway View of Reflectometers Beamlines from Source Through Shutter
Reflectometer Beam Lines at the SNS
� Similar approach may work for fundamental physics beam lines.
� Secondary shutters for independent operation.Possible because benders greatly reduce high-energy component of beam.
Magnetism
Liquids
Reflectometer Beam Lines at the SNS
� Heavily shielded until end of guides with high-density concrete.Plan < 2 mR/hr inside �caves� and 0.25 mR/hr outside (SNS requirement).
� First choppers (near 5 m), may need to be smaller than standard size due to limited space.Probably no t0 choppers.
3 Choppers
Neutron Guide
High-density Concrete Shielding
Magnetism Reflectometer
Possible Layout of Single and Dual Beam Lines for Fundamental Physics
� Benders (blue) depart from line-of-sight (green) at 6.8 m.Benders from 2.2 to 6.2 m, both clockwise.
� n + p → d + γ apparatus drawn at end of 15-m guide.
� 25-m guide on BL14A with and w/o second bender.Second bender (3 degrees in 3 m) increases distance fromBL13 shielding from 1.25 m to 1.66 m.
Close-up of Shutter and Bender� Possible to extend guide to within 1 m of source.
BL14A rotated the maximum allowed by shutter so thatit doesn�t overlap 14B outside 1 m from moderator.
� Benders are segmented, with 0.25 degree steps every 0.5 m.
� Guides depart from line-of-sight at 6.8 m from source.Guides shown in blue.Line of sight, and possible extension of guides to within 1 m ofmoderator, shown in green.
R (m) Space (m)BL13 BL14
10 2.3 2.715 3.4 4.120 4.5 5.525 5.7 6.830 6.8 8.2
Simulations for Fundamental Physics Beam Lines
� Used program �IB� by J. K. Zhao.Monte Carlo code to trace neutrons through guides, etc.Uses Excel to generate input files for MC �engine�.Has library of benders, segmented guides, tapered guides, detectors (x-y, x-θ, y- θ vs. λ).
Ex: Bender
Can vary position, height, width, number of channels, radius, offset angle, Rc, R0, m.
Used to calculate transmissions through guides and fluxes at end of guides.
0 5 10 15
Wavelength (A)
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Flux
(108 n
eutr
ons/
cm2 /s
/A)
BLC6Flux Sept. 5, 2001 1:42:40 PM
Guide Simulation with IB
Divergence=6.90
m=3.5R0=98%
Rc=80%
Straight GuideR=114 m BenderR=57 m Bender
10x12 cm Guide from 1 to 15 m Beam 2 m Downstream of End of 10x12 cm Guideλ = 9 A
IB simulations
� Used latest calculated moderator intensities from Erik Iverson scaled from 2.0 MW to 1.4 MW.
� Impact on flux of:Straight vs. curved guides.Starting guide at 1 m (closest approach) vs. 2.2 m (start of shutter).Different guide lengths.50-cm gap for possible t0 chopper.
� Profile of beam.How much does beam spread downstream of guide?Affect of wavelength on beam profile.
Coupled hydrogen
Water
Decoupled hydrogen
Impacts of Different Guide Configurations
� 50-cm gap at 5.3 m for t0 chopper.Straight.15 m long.10 x 12 cm.
� Curved vs. straight,15 m long.20 benders starting 2.2 m from source.10 x 12 cm.
0 5 10 15Wavelength (A)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Rat
io o
f Flu
xes
m=3.5R0=98%Rc=80%
Gap/No Gap
10x12 cm Straight Guide from 1 to 15 m
0 5 10 15Wavelength (A)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Rat
io to
Flu
x fr
om S
trai
ght G
uide
m=3.5R0=98%Rc=80%
R=57 mR=114 m Bender
10x12 cm Guide from 1 to 15 m
Guide Fluxes 0.5 to 15 AStraight 2.79x109 n/s/cm2
R=114 m 2.04x109
R=57 m 1.74x109
Impacts of Different Guide Configurations
� Impact of starting guide at 1 vs. 2.2 m.Bender begins at 2.2 m (start of shutter).
10x12 cm guide.
20 bender.
� Impact of length of guide.15 m vs. 25 m.
25-m guide starts at 1 m.
15-m guides start at 1, 2.2 m.
0 5 10 15Wavelength (A)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Ratio
of F
luxe
s
R=57 mR=114 m
Ratio of Fluxes for Guides Starting at 1.0/2.2 m
0 5 10 15Wavelength (A)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Flux
of 2
5-m
Gui
de/F
lux
of 1
5-m
Gui
de
m=3.5R0=98%Rc=80%
15-m guide starts at 1 m15-m guide starts at 2.2 m
10x12 cm Guide with 20, R=114 m Bender
Comparison to LANSCE
� Calculated LANSCE FP12 flux from Seppo PenttilaAssumes 200 µA at 20 Hz (160 kW).Guide: 9.5x9.5 cm, m=3, 16.61 m long. Starts 137.2 cm from
12.5x12.5 cm moderator.Scaled by: 1.37 for FP11a measurement vs. LAHET fit.
1.5 for FP12 vs. FP11a from as-built calculation.0.8 for attenuation due to windows in flight path.
� Calculated SNS flux assumes:Guide: 10x12 cm, m=3.5, 15 m long. Starts 1.0 m from 10x12
moderator. 20 bender.Assumes 1.44 MW (9.0 times LANSCE power).
0 2 4 6 8Wavelength (A)
101
102
103
Flux
(106 n
eutro
ns/c
m2 /s
/A)
LANSCESNS, Straight GuideSNS, R=114 m BenderSNS, R=57 m Bender
Beam Contours
� Guide from 1 to 15 m with R=114 m, 20 bender.� 2 m downstream of end of guide.� Minimum count plotted is 5% of maximum.
-10 -5 0 5 10Height (cm)
-10
-5
0
5
10
Wid
th (c
m)
λ=3 A
-10 -5 0 5 10Height (cm)
-10
-5
0
5
10
Wid
th (c
m)
λ=5 A
-10 -5 0 5 10Height (cm)
-10
-5
0
5
10
Wid
th (c
m)
λ=7 A
-10 -5 0 5 10Height (cm)
-10
-5
0
5
10
Wid
th (c
m)
λ=9 A
Choppers
� For 60 Hz, maximum wavelength bite given by:
∆λ(A) = 65.9/L(m).
� To avoid possible backgrounds near t0, phase choppers to select regions 0 � ∆λ, ∆λ � 2∆λ, 2∆λ � 3∆λ.
0 5 10 15Wavelength (A)
0.0
1.0
2.0
3.0
4.0
5.0
Flux
(108 n
eutro
ns/c
m2 /s
/A)
Chopper Regions for 17 m, 60 Hz
∆λ = 3.88 A
1 2 3
Region n/cm3
1 60002 128003 6200
2.4-6.3 A 14686
10x12 cm guide from 1-15 m, R=114 m, 20 bender
Choppers
� Three choppers planned for reflectometers. Similar approach may work for fundamental physics cold neutron experiments.
Distance (m) Opening Angle (0)5.3 1137.3 1549.1 191
0
2
4
6
8
10
12
14
16
18
0 20 40 60 80 100 120
time [ms]
Dis
tanc
e fro
m s
ourc
e [m
]
3.87Å3.94Å7.72Å7.78ÅT0T1T2T-optionalT-definition11.18Å15.03Å18.43Å22.28Å29.52ÅTest Line 0.1A
Chopper Timing Diagram for Second Frame
31
Chopper Disk
10x12Guide
Resolution at 9 A
� Adapted from SNS/TSR-203 by Erik Iverson.� At 9 A, ∆t = 230 µs
For L=26 m, ∆t/t = 0.37% => ∆E = 7.4 µeV.� For production of UCN in LHe, ∆E 0.5 µeV.� Design chopper for ∆t = 230 µs ⇒ ≈ 7% of neutrons in band
for conversion to UCN in LHe.� Flux in SNS resolution, φ1 = 2.1x106 n/s/cm2.� Flux in LHe �band�, φ2 = 1.5x105 n/s/cm2.
0 5 10 15 20λ (A)
0
100
200
300
400
∆t (µ
s)
SNS Coupled H2 Moderator
∆t=23+224*log(λ)-8*log(λ2)
∆t = 230 µs at 9 A
Important Questions
� Which beam line is best?
Dual (14A&B)?Single (13 or 15)?
� Guide in �core vessel insert?�
Significant gain in flux if guide begins in this region.Radiation damage?Access?
� Lengths and types of guides?
Straight or curved?Tapered?
� Number and type of choppers needed?
t0?Approach for LHe?Mirror wedge to exclude long-wavelength neutrons?
Pros and Cons of Dual Beam Line
� Pro.
Two independent, �permanent� beamlines optimized for two classes of fundamental physics experiments.
� Cons.
Flux may be reduced because may not be able to get guide as close to moderator as for single beam line case.
Less room for experiments.
Possibly higher backgrounds (but if good enough for reflectometers, probably good enough for us).
Space for first choppers is tight. Requires special design (borrow from reflectometers). May not be able to have t0 chopper.
