RAL Template

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The T2K Beam Window
Matt Rooney Rutherford Appleton Laboratory BENE
November 2006
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Contents

• The T2K target station beam window
• - Design
• - Dynamic stress analysis
• Implications for beam windows at higher powers
• - T2K upgrade
• - Limits of windows

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T2K Beam Window Overview
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T2K Target Station
Window
Proton beam
Focusing horns
Target
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Beam Parameters

• 0.75 MW beam energy
• Gaussian profile with 4 mm rad rms beam spot
• 5 µs pulse 8 x 58ns bunches
• 1 pulse every 2 seconds at 30 GeV

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Beam Window - Requirements

• Withstand 1 atm pressure difference
• Endurance against temperature rise and thermal
  stress due to pulsed proton beam
• Beam loss must be less than 1, i.e. it must be
  thin
• Structure should be remotely maintained

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Beam Window Assembly

• Window Overview
• - Double skinned partial hemispheres, 0.3 mm
  thick.
• Helium cooling through annulus.
• Ti-6Al-4V.
• Inflatable pillow seal on either side.
• Inserted and removed remotely from above.

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Window Assembling
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Helium cooling
Upstream
Annulus
Helium velocity 5 m/s Heat transfer coefficient
150 W/m2K
Downstream
He in
He out
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Remote handling
Target station
Beam Position Monitor chamber
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Dynamic Stress Analysis
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Transient window temperature
Heat transfer coefficient 140 Wm2/K external
and 10 W/m2K internal Beam energy 50
GeV Frequency 0.284
Simulation shows temperature distribution over 5
pulses (15 seconds)
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Stress Waves
Stress wave development in 0.6 mm constant
thickness hemispherical window over first 2
microbunches.
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0.62mm Window - Constructive Interference
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0.3mm Window - Destructive interference
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Important lesson

• With a pulsed proton beam, window and target
  geometry can greatly affect the magnitude of
  stress.
• Be careful to check dynamic stress when changing
  beam parameters or target and window geometry!

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Higher Power
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T2K 3 MW upgrade

• Increased number of protons per pulse would push
  the limits of Ti-6Al-4V.
• 0.75 MW pulse 100 MPa shock stress
• 3.0 MW pulse 500 MPa shock stress
• Room temp yield strength Ti-6Al-4V 900 MPa.
• But higher power could also be achieved through a
  higher beam frequency.

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Future Neutrino Factories and Super-beams

• Higher beam current through higher frequency.
• Less PPP, smaller beam spot.
• Adequate cooling and material selection can
  mitigate for high energy deposit and thermal
  shock.
• Radiation damage becomes dominant effect.

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Radiation effects

• Irradiation affects different materials in
  different ways
• - Many metals lose ductility.
• - Graphite loses thermal conductivity.
• - Coefficient of Thermal Expansion of super
  invar increases, but low CTE can be recovered by
  annealing.

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Conclusions
More RD needed for beam power upgrades. Irradiat
ed material data is crucial. This should be a
major research priority in the coming years.
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THANK YOU! QUESTIONS?