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The T2K Beam Window

The T2K Beam Window. Matt Rooney Rutherford Appleton Laboratory BENE November 2006. Contents. The T2K target station beam window - Design - Dynamic stress analysis Implications for beam windows at higher powers - T2K upgrade - Limits of windows. T2K Beam Window Overview.

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The T2K Beam Window

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

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

  3. T2K Beam Window Overview

  4. T2K Target Station Window Proton beam Focusing horns Target

  5. 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

  6. Pulsed proton beam Vacuum Window He @ 1 atm Graphite target 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

  7. 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.

  8. Top plate • Used for inserting and removing window • Protects pillow seals and mating flanges • Provides a connection point for services • Pillow seals • Seal helium vessel and beam line • (leak rate spec, 1 x 10-7 Pa……) • Side plates • Provide a firm support for the beam window to hold it in position Ti-6Al-4V beam window Window Assembling

  9. Helium cooling Upstream Annulus Helium velocity ≈ 5 m/s Heat transfer coefficient ≈ 150 W/m2K Downstream He in He out

  10. Remote handling Target station Beam Position Monitor chamber

  11. Dynamic Stress Analysis

  12. 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)

  13. Stress Waves Stress wave development in 0.6 mm constant thickness hemispherical window over first 2 microbunches.

  14. 0.62mm Window - Constructive Interference

  15. 0.3mm Window - Destructive interference

  16. 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!

  17. Higher Power

  18. 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.

  19. 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.

  20. 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.

  21. Conclusions More R&D needed for beam power upgrades. Irradiated material data is crucial. This should be a major research priority in the coming years.

  22. THANK YOU! QUESTIONS?

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