shock tests on tantalum and tungstenmcdonald/mumu/...nt() m,0.7 tm 2 cm diameter target. a larger...
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Shock Tests on Tantalum and Tungsten
J. R. J. Bennett, S. Brooks, R. Brownsword, C. Densham, R. Edgecock, S. Gray, A. McFarland, G. Skoro and D. Wilkins.
CCLRC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK
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The original RAL Target concept -(after Bruce King)
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Schematic diagram of the radiation cooled rotating toroidal target
rotating toroid
proton beam
solenoid magnet
toroid at 2300 K radiates heat to water-cooled surroundings
toroid magnetically levitated and driven by linear motors
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The alternative concept –
Individual Bar Targets
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Target ParametersProton Beam
pulsed 50 Hz pulse length ~40 μsenergy ~10 GeVaverage power ~4 MW
Target (not a stopping target)
mean power dissipation 1 MWenergy dissipated/pulse 20 kJ (50 Hz)energy density 300 J cm-3 (50 Hz)
2 cm
20 cm
beam
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It is not possible to test the full size targets in a proton beam and do a life test.
Produce shock by passing high current pulses through thin wires.
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Pulsed Power Supply.0-60 kV; 0-10000 A
100 ns rise and fall time
800 ns flat top
Repetition rate 50 Hz or sub-multiples of 2
Coaxial wires
Test wire, 0.5 mm Φ
Vacuum chamber, Vacuum chamber, 2x102x10--77 --1x101x10--66 mbarmbar
Schematic circuit diagram of the wire test equipment
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turbopump
Penning gauge
window
window
tantalum wire
ISO 63 teebulkhead high voltage
feed-throughs
ct
Schematic section of the wire test assembly
Co-axial cables
Top plate
ISO 63 cross
support rods
Electrical return copper strip
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Vertical Section through the Wire Test Apparatus
Current
Inner conductor of co-axial insulator feed-through.
Stainless steel split sphere
Copper “nut”
Current
Two graphite (copper) wedges
Tungsten wire
Spring clips
Fixed connection
Sliding connection
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Need to independently vary the pulse current (energy density dissipated in the wire) and the peak temperature of the wire. (Not easy!)
1. Can vary the repetition rate (in factors of two).
2. Can vary the wire length which changes the cooling by thermal conduction to the end connections.
Must not fix both ends of the wire!
Some problems encountered with getting reliable electrical end connections, particularly the top sliding connection.
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Picture of the pulse current
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Picture of the wire test equipment
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Photograph of the tantalum wire showing characteristic wiggles before failure.
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A broken tantalum wire
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Some Results of 0.5 mm diameter wires
36-
48
24
Beam PowerMW
4.2x106
+PLUS+>6.5x106
>1.6x106
>3.4x106
0.2x106
No. of pulses to failure
1900
2050
1900
2000
1800
Max. Temp
K
23-
12.5
12.5
130
140
5560
5840
2.5Not broken;
still pulsing
23
6.2517064003Stuck to top Cu connector
23
12.510049003Broke when increased to 7200A (2200K)
TungstenTantalum is not a very good material – too weak at high temperatures.
12.56030004Tantalum
Target diacm
Rep RateHz
Pulse Temp.
K
Pulse Current
A
Lngth
cm
Material
“Equivalent Target”: This shows the equivalent beam power (MW) and target radius (cm) in a real target for the same stress in the test wire. Assumes a parabolic beam distribution and 4 micro-pulses per macro-pulse of 30 μs.
Equivalent Target
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Tungsten is a good candidate for a solid target and should last for several years.
In this time it will receive ~10-20 dpa. This is similar to the 12 dpa suffered by the ISIS tungsten target with no problems.
Tantalum is too weak at high temperatures to withstand the stress.
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The Number of Bars
and
the Number of Pulses
(1 year is taken as 107 s)
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At equilibrium, a target bar heats up in the beam and then cools down by the same amount before entering the beam again.
A new bar enters the beam at the rate of 50 Hz. i.e. every 20 ms.
The more bars there are in the system then the fewer times any one bar goes through the beam in a year and the lower is the peak maximum temperature.
This is illustrated in the next overhead (for two different thermal emissivities) where the number of bars and the number of pulses each bar will receive in 1 yr (107 s) is plotted against the pulse temperature.
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ε = 0.27
ε = 0.27
ε = 0.7ε = 0.7
1400 1500 1600 1700 1800 1900 2000 2100 2200 23000
200
400
600
800
1000
1200
1400
1600
0
2.106
4.106
6.106
8.106
1.107
1.2.107
1.4.107
1.6.107Number of Bars and Number of Pulses per Year as a Function of Peak Temperature and Thermal Emissivity
Peak Temperature, K
Num
ber o
f Bar
s
Num
ber o
f Pul
ses i
n 1
year
N Tm 0.27,( )N Tm 0.7,( )
n Tm 0.27,( )n Tm 0.7,( )
Tm
2 cm diameter target
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A larger diameter target reduces the energy density dissipated by the beam (beam diameter = target diameter).
So going from 2 to 3 cm diameter reduces the energy density by a factor of 2 and the stress is also correspondingly reduced.
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1400 1500 1600 1700 1800 1900 2000 2100 2200 23000
100
200
300
400
500
600
700
800
900
1000
0
2 .106
4 .106
6 .106
8 .106
1 .107
Number of Bars and Number of Pulses per year as a function of Peak Temperature and Thermal Emissivity
Peak Temperature, K
Num
ber o
f Bar
s
Num
ber o
f Pul
ses i
n 1
year
N Tm 0.27,( )N Tm 0.7,( )
n Tm 0.27,( )n Tm 0.7,( )
Tm
3 cm diameter target
ε = 0.27
ε = 0.27
ε = 0.7
ε = 0.7
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I believe that a solid tungsten target is viable from the point of view of
shock
and
radiation damage.
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Target Mechanics
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The original scheme
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πprotons in
protons to dump
shielding
shielding
solenoidal capture magnet
B field
Cu-Ni band target
target band
x
z
Target Geometry
Bruce King
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Typical Schematic Arrangement of a Muon Collider Target
targetprotons
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A possible alternative scheme
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Schematic diagram of the target and collector solenoid arrangement
solenoids
Target BarsTarget Bars
The target bars are connected by links -like a bicycle chain.
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or
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Solenoid
Target BarsTarget Bars
Slot in solenoid
Schematic diagram of the collector solenoid with a slot for the target bars.
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A A
Section AA
Plan View
A possible way of linking the targets
TargetLink
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Chain Sprocket for the rear of the bars
Target Bar Chain Links
Schematic arrangement of the chain mechanism for the target bars
Chain Sprocket for the front of the bars
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Lorenz + Thermal Force
Lorenz ForceThermal Force
100 ns pulse
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A possible arrangement of the solenoids
Magnetic Field
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Protons after hitting the target
Remnant ~9.5 GeV proton beam; Large angle; 20%
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Remnant proton beam. Shallow angle.
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Captured Yield from Tantalum Target
0%
20%
40%
60%
80%
100%
120%
0 0.5 1 1.5 2 2.5 3 3.5 4
Rod and Beam Radius (cm)
Rel
ativ
e Ef
ficie
ncy
mu+ (2.2GeV)mu- (relative to 1cm)mu+ (30GeV)mu-
We can expect ~94.5% of the yield to remain going from a 1cm to a 1.5cm radius beam and target.
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Pion Yield for different target lengths