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

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

3. Matt Rooney RAL T2K Beam Window Overview

4. Matt Rooney RAL T2K Target Station Proton beam Focusing horns Target Window

5. Matt Rooney RAL 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. Matt Rooney RAL 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 Pulsed proton beam Vacuum He @ 1 atm Window Graphite target

7. Matt Rooney RAL 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. Matt Rooney RAL Window Assembling Side plates -Provide a firm support for the beam window to hold it in position 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……) Ti-6Al-4V beam window

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

10. Matt Rooney RAL Remote handling Beam Position Monitor chamber Target station

11. Matt Rooney RAL Dynamic Stress Analysis

12. Matt Rooney RAL Transient window temperature Simulation shows temperature distribution over 5 pulses (15 seconds) Heat transfer coefficient = 140 Wm2/K external and 10 W/m2K internal Beam energy = 50 GeV Frequency = 0.284

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

14. Matt Rooney RAL 0.62mm Window - Constructive Interference

15. Matt Rooney RAL 0.3mm Window - Destructive interference

16. Matt Rooney RAL 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. Matt Rooney RAL Higher Power

18. Matt Rooney RAL 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. Matt Rooney RAL 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. Matt Rooney RAL 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. Matt Rooney RAL 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. Matt Rooney RAL THANK YOU! QUESTIONS?