Shock Tests on Tantalum and Tungsten

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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. roger.bennett_at_rl.ac.uk 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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The alternative concept Individual Bar Targets
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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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Test wire, 0.5 mm F
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
Vacuum chamber, 2x10-7 -1x10-6 mbar
Schematic circuit diagram of the wire test
equipment
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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!)
• Can vary the repetition rate (in factors of
  two).
• 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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• 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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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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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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Bruce King
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A possible alternative scheme
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or
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Thank You The End
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Lorenz Force
Thermal Force
Lorenz Thermal Force
100 ns pulse
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Magnetic Field
A possible arrangement of the solenoids
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Remnant 9.5 GeV proton beam Large angle 20
Protons after hitting the target
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Remnant proton beam. Shallow angle.
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Pion Yield for different target lengths