This document summarizes a workshop on multi-megawatt spallation neutron sources held from March 16-18, 2009 in Bilbao, Spain. Topics discussed included current challenges such as target design and testing, and future prospects such as higher power targets. Specific issues addressed were mercury flow dynamics, bubble formation, and surface texturing to reduce damage from cavitation. Simulation and experimental results on bubble size and coalescence were also presented.

1. ESS Bilbao Initiative Workshop
Multi-MW Spallation Neutron Sources:
Current Challenges and Future Prospects
March 16-18, 2009
Bilbao, Spain

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3. Target-to-core vessel
inflatable seal
Mercury vessel
Target-to-Hg
piping seal
Water shroud
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Mercury filled test target being Simulation of test target response to
prepared for in-beam test beam show mercury pressure evolution
[Pa]
Mercury in state of cavitation
What is the tensile strength of mercury?
1.5 bar
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50.8 mm
25.4 mm
Bubbler #1 Storage
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Mercury Pump
1.5 mm
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A B C
Bubbler #1 Bubbler #2 Bubbler #2
Helium Argon Helium
Series average Series average Series average
VF = 3.56E-04 VF = 1.34E-03 VF = 1.37E-03
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B1 01D-S01_04D-S02S07S08 140 sccm, Total VF = 1.29E-03
B2 140 sccm, Total VF = 4.74E-03
04D-S09S11
1.6E-03
B1 04Dec06State03 300 sccm, Total VF = 2.61E-03
B2
Number density [n/mm ]
300 sccm, Total VF = 3.46E-03
04Dec06State10
3
1.4E-03
1.2E-03
Smallest bubble:
0.12 mm equivalent radius.
1.0E-03
8.0E-04
Corresponds to 2005
damage test condition.
6.0E-04
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0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2
Radius [mm]
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21. 6.0
A Edge
Bubble Diameter [mm]
Transmission
5.0
Acoustic
4.0
UL = 0
3.0
2.0
1.0
UL = 0 ; QHe = 10 sccm 0.0
4.5
B 4.0
Bubble Diameter [mm]
UL = 0.63 m/s
3.5
3.0
2.5
2.0
1.5
1.0
0.5
UL = 0.63 m/s; QHe = 10 sccm
0.0
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C
Bubble Diameter [mm]
2.5 UL = 0.96 m/s
2.0
1.5
1.0
0.5
UL = 0.63 m/s; QHe = 100 sccm
0.0
0.1 1 10 100 1000
Gas flow rate [SCCM]
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bubble coalescence
Db =1.196 mm Db =1.049 mm
Fluent
CFX
Db =1.064 mm (measured)
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24. )
SNS Target configuration
TTF Target only has main flow
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Ri = 41 mm
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Mercury flow quasi-
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Viewport
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Mercury flow left to right
Gas Injected at this Nozzle
Vertical grooves (0.5 mm pitch, V 30 deg)
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33. 2010 - .
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Flow guides
increase flow
Hg Flow
velocity to more
prototypic SNS
conditions
Test surface with
33 mm
surface texturing
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HIGH intensity
1 σ_X = 13.5 mm
1 σ_Y = 4.5 mm
2σ
Rectangular target interior
4.8 MW SNS eq,
1.625 x 5.625”
MEDIUM intensity
1 σ_X = 21 mm
1 σ_Y = 7 mm
2σ
2.0 MW SNS eq.
LOW intensity
1 σ_X = 30 mm
1 σ_Y = 10 mm
2σ
1.0 MW SNS eq.
Total energy deposited in targets is maintained between conditions.
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Intensity varied by changing beam spot size.
for the U.S. Department of Energy

37. 1
protons / Maximum
σ_X σ _Y
Target – Test No. of Pulses pulse length Comment
pulse Intensity
µ
x 1012 [µs] [mm] [mm] [p/mm2 x 1010]
(approx.) (half width) (half height)
LDV & PCD testing. Varied
RECT – LDV
95 0.1 – 27 0.3 14.8 – 33.6 4.6 – 10.4 5.6 intensities by changing profile and
various beam
protons
RECT – High Request smallest possible beam
100 26.5 0.3 15.4 5.2 5.25
Intensity spot with 3:1 aspect ratio
RECT – Medium This condition roughly splits low
100 26.6 0.3 20.2 6.1 3.43
Intensity and high
RECT – Low This is about the largest beam that
100 26.3 0.3 32.5 9.5 1.36
fits inside target at 2 σ
Intensity
RECT – textured Cone type textured test surface;
100 26.5 0.3 21.2 6.7 2.95
surface Gas puffing suspected not correct
RECT – Long Long pulse beam conditions still
100 45 ? 833 20.4 6.1 6.0 ?
pulse under study
Primary damage dependence on intensity scope
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Velocity (m/s)
-1
-2
1.2 1.4 1.6 1.8 2
Time (ms)
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40. 1. Band pass velocity data (15 – 300 kHz)
Omit 10 µs after pulse
2.
0.1
High
CPD = V 2 dt
intensity
CDP (mm2/s)
Medium
intensity
0.05
Low intensity
Interesting artifact is consistent
2 ms after incidence
0
2 3 4
Time (ms)
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