stephen brooks / [email protected] uknf meeting, warwick, april 2008 pion production from...
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Stephen Brooks / [email protected]
UKNF meeting, Warwick, April 2008
Pion Production fromWater-Cooled Targets
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Contents
1. Recap of current UKNF solid target
2. Pros and cons related to water cooling
3. Results from MARS 15.07– Including water in & lengthening the target– Pion yield (reabsorption)– Additional heating– Pion temporal distribution
• Conclusions
Stephen Brooks / [email protected] meeting, Warwick, April 2008
1. Recap of current UKNF solid target
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Traditional UKNF Solid Target
• p+ target +,− +,− neutrinos
• Radiation-cooled solid rods of tungsten– Replaced every 50Hz beam pulse by chain or
wheel (~200 in whole loop)
• 2-3cm diameter, 20-30cm length
• Inside initial 20T solenoidal capture field– Usable bore ~20cm diameter– Pions tend to spiral in magnetic field
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Main Design Problems
• Direct heating of the target from energy deposition
• Pions becoming reabsorbed– Target being too wide– Re-entering the target due to magnetic field
• Reabsorption produces more heating!
• A total of 20-30cm of high-Z target material thickness seems optimal
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Where does the proton beam power go?
12.9%
24.3%
62.8%
Heat deposited in target
Kinetic energy of protons within5° of forward axis
Kinetic energy of other (diffuse)secondaries, including pions
Figures from a 10GeV proton beam (ISS baseline) hitting a 20cm long, 2cm diameter tantalum rod target
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Muon Transmission from MARS15-Generated Pions
3
GeV
4
GeV
8
GeV
4
0GeV
5
0GeV
7
5GeV
1
00G
eV
120
GeV
3
0GeV
6G
eV
2
.2G
eV 1
5GeV
1
0GeV
5
GeV
2
0GeV
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
1 10 100 1000
Proton Energy (GeV)
Pio
ns p
er P
roto
n.G
eV (e
st. C
hica
ne/L
inac
)
pi+/(p.GeV)
pi-/(p.GeV)
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Energy Deposition in Rod (heat)
• Scaled for 5MW total beam power
2.2G
eV
3GeV
4GeV
5GeV
6GeV
8GeV
10G
eV
15G
eV
20G
eV 30G
eV
40G
eV50
GeV
75G
eV
100G
eV12
0GeV
0
200000
400000
600000
800000
1000000
1200000
1400000
1 10 100 1000
Proton Energy (GeV)
Po
wer
Dis
sip
atio
n (
Wat
ts,
no
rmal
ised
to
5M
W
inco
min
g b
eam
)
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Not Multi-Megawatt Heating
Machine Beam power Proton energy Heating power
ISS beam 4MW 10GeV 514kW
UK neutrino factory scenarios
4MW 8GeV 512kW
5MW 10GeV 643kW
5MW 8GeV 640kW
neutron source
169kW 800MeV211A
169kW ×1
×3
×4
Stephen Brooks / [email protected] meeting, Warwick, April 2008
2. Pros and cons related to water cooling
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Why it “wouldn’t work”
• Additional water would reabsorb too many pions– It would also increase heating in itself
• Increasing the target length would increase longitudinal time-spread of pions– 1m length = 3ns > 1ns RMS of proton beam
• Water-cooling has a maximum of 1MW– Would require 50% water in the small target
Stephen Brooks / [email protected] meeting, Warwick, April 2008
False Assumptions Corrected
• Additional water would reabsorb too many pions– Water = 1.0 g/cc, tungsten = 19.2 g/cc
• Increasing the target length would increase longitudinal time-spread of pions– Pions of interest >250 MeV/c momentum
– > 0.87, protons = 0.996, only lag matters
• 1MW is enough capacity
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Advantages of Water Cooling
• Conventional technology– Many examples in operation
• Including elsewhere in the target assembly! E.g. cooling for the normal-conducting solenoids
– No solid moving parts (apart from pumps)– Radioactive flow loop isn’t liquid mercury
• Although there is still some tritium to deal with
• All parts of target stay below about 200°C
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Disadvantages of Water Cooling
• Water will cavitate if the instantaneous temperature rise is too high, erode walls– Also if the flow rate is too high for pressure
• Flow manifold has to be somewhere and enter/exit the target
• Pressures may have to be large to induce sufficient flow rate
• Relies on fluid dynamics, requires much more careful design than in this talk
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Naïve Flow Rate Calculation
• Assumes perfect:– Conductivity of metal target pieces– Thermal conduction from target to water– Mixing of water
• Pin = 700kW; T = 50K
• Flow rate 3.34 kg/s
• Speed 10.6 m/s for 2cm diameter pipe– Will be more than this realistically
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Simulation Geometry
Protons
20cm, 50cm, 1m, 2m
2,3,4,5cm
Bz = 20T 10cm radius
Particles logged at end-plane
Particles removed outside bore
Parallel beam, circular parabolic distribution, 2cm diameter
WaterTantalum “coin”, 2mm thick 100 coins in target for 20cm total Ta thickness
4×4 = 16 runs
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Three Figures of Merit
• Useful pion yield– Weighted depending on (pL,pT) momenta
• Amount of heating in the system– How much does the water contribute?
• Time-spread acquired from long target– Only interested in “useful” pions here too
Stephen Brooks / [email protected] meeting, Warwick, April 2008
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.01L
20cm
R
1cm
L 20
cm
R 1
.5cm
L 20
cm
R 2
cm
L 20
cm
R 2
.5cm
L 50
cm
R 1
cm
L 50
cm
R 1
.5cm
L 50
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cm
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.5cm
L 10
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cm
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cm
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R
1cm
L 20
0cm
R
1.5
cm
L 20
0cm
R
2cm
L 20
0cm
R
2.5
cm
pi+/(p.GeV)
pi-/(p.GeV)
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.01L
20cm
R
1cm
L 20
cm
R 1
.5cm
L 20
cm
R 2
cm
L 20
cm
R 2
.5cm
L 50
cm
R 1
cm
L 50
cm
R 1
.5cm
L 50
cm
R 2
cm
L 50
cm
R 2
.5cm
L 10
0cm
R
1cm
L 10
0cm
R
1.5
cm
L 10
0cm
R
2cm
L 10
0cm
R
2.5
cm
L 20
0cm
R
1cm
L 20
0cm
R
1.5
cm
L 20
0cm
R
2cm
L 20
0cm
R
2.5
cm
pi+/(p.GeV)
pi-/(p.GeV)
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.01L
20cm
R
1cm
L 20
cm
R 1
.5cm
L 20
cm
R 2
cm
L 20
cm
R 2
.5cm
L 50
cm
R 1
cm
L 50
cm
R 1
.5cm
L 50
cm
R 2
cm
L 50
cm
R 2
.5cm
L 10
0cm
R
1cm
L 10
0cm
R
1.5
cm
L 10
0cm
R
2cm
L 10
0cm
R
2.5
cm
L 20
0cm
R
1cm
L 20
0cm
R
1.5
cm
L 20
0cm
R
2cm
L 20
0cm
R
2.5
cm
pi+/(p.GeV)
pi-/(p.GeV)
Useful Pion Yield1000 protons10000 protons50000 protons
3x50cm gives 94.4% of 2x20 (solid)3x100 gives 90.8%
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Amount of Heating
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
L 20
cm
R 1
cm
L 20
cm
R 1
.5cm
L 20
cm
R 2
cm
L 20
cm
R 2
.5cm
L 50
cm
R 1
cm
L 50
cm
R 1
.5cm
L 50
cm
R 2
cm
L 50
cm
R 2
.5cm
L 10
0cm
R
1cm
L 10
0cm
R
1.5
cm
L 10
0cm
R
2cm
L 10
0cm
R
2.5
cm
L 20
0cm
R
1cm
L 20
0cm
R
1.5
cm
L 20
0cm
R
2cm
L 20
0cm
R
2.5
cm
0
200000
400000
600000
800000
1000000
1200000
1400000
Energy deposition proportion intantalum
Energy deposition in water
Total heating for 4MW beam
3x50cm gives 644kW heating3x100 gives 488kW
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Arrival Time Distribution2m length
0
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4500
5000
1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 201 211 221 231 241
Arrival time (10 bins = 1ns)
All pions
Useful pions
1m length
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 201 211 221 231 241
Arrival time (10 bins = 1ns)
All pions
Useful pions
50cm length
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 201 211 221 231 241
Arrival time (10 bins = 1ns)
All pions
Useful pions
20cm length
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 201 211 221 231 241
Arrival time (10 bins = 1ns)
All pions
Useful pions
(2cm diameter rod)
Stephen Brooks / [email protected] meeting, Warwick, April 2008
RMS of Useful Arrival Times
0
0.5
1
1.5
2
2.5
3
3.5L
20cm
R
1cm
L 20
cm
R 1
.5cm
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cm
R 2
cm
L 20
cm
R 2
.5cm
L 50
cm
R 1
cm
L 50
cm
R 1
.5cm
L 50
cm
R 2
cm
L 50
cm
R 2
.5cm
L 10
0cm
R
1cm
L 10
0cm
R
1.5
cm
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0cm
R
2cm
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R
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cm
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0cm
R
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cm
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0cm
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R
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cm
RM
S t
ime-
spre
ad (
ns)
Instantaneousbeam
Combined with1ns RMS protontime-spread
Combined with3ns RMS protontime-spread
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Modified Geometry
Protons
20cm, 50cm, 1m, 2m
2mm thickness stainless steel outer tube
WaterTantalum “coin”, 2mm thick 100 coins in target for 20cm total Ta thickness
4×4 = 16 runs
3mm thickness additional water outside main target
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Modified Pion Yield
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.01L
20cm
R
1cm
L 20
cm
R 1
.5cm
L 20
cm
R 2
cm
L 20
cm
R 2
.5cm
L 50
cm
R 1
cm
L 50
cm
R 1
.5cm
L 50
cm
R 2
cm
L 50
cm
R 2
.5cm
L 10
0cm
R
1cm
L 10
0cm
R
1.5
cm
L 10
0cm
R
2cm
L 10
0cm
R
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cm
L 20
0cm
R
1cm
L 20
0cm
R
1.5
cm
L 20
0cm
R
2cm
L 20
0cm
R
2.5
cm
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
pi+/(p.GeV)
pi-/(p.GeV)
pi+ with tube
pi- with tube
Ratio(pi+)
Ratio(pi-)
3x50cm: 94.4% 91.9% of 2x20 (solid)3x100: 90.8% 82.7%
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Amount of Heating
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
L 20
cm
R 1
cm
L 20
cm
R 1
.5cm
L 20
cm
R 2
cm
L 20
cm
R 2
.5cm
L 50
cm
R 1
cm
L 50
cm
R 1
.5cm
L 50
cm
R 2
cm
L 50
cm
R 2
.5cm
L 10
0cm
R
1cm
L 10
0cm
R
1.5
cm
L 10
0cm
R
2cm
L 10
0cm
R
2.5
cm
L 20
0cm
R
1cm
0
200000
400000
600000
800000
1000000
1200000
1400000
Energy deposition proportion intantalum
Inner water
Water tube
Steel tube
Total water
Total heating for 4MW beam
Total without tube
3x50cm: 644 737kW heating3x100: 488 616kW
Stephen Brooks / [email protected] meeting, Warwick, April 2008
RMS of Useful Arrival Times
0
0.5
1
1.5
2
2.5
3
3.5L
20cm
R
1cm
L 20
cm
R 1
.5cm
L 20
cm
R 2
cm
L 20
cm
R 2
.5cm
L 50
cm
R 1
cm
L 50
cm
R 1
.5cm
L 50
cm
R 2
cm
L 50
cm
R 2
.5cm
L 10
0cm
R
1cm
L 10
0cm
R
1.5
cm
L 10
0cm
R
2cm
L 10
0cm
R
2.5
cm
L 20
0cm
R
1cm
RM
S t
ime-
spre
ad (
ns)
Instantaneousbeam
Combined with1ns RMS protontime-spread
Combined with3ns RMS protontime-spread
Stephen Brooks / [email protected] meeting, Warwick, April 2008
Conclusions
• The neutrino factory requirements do not seem to preclude a water-cooled target– Fast particle production targets can have a
much lower % heat load than slow targets
• Does this also mean an SNS-style enclosed mercury target might work?
• Need to investigate in more depth to either verify or exclude these options