Matt Rooney

RAL

The T2K Beam Window

Matt RooneyRutherford Appleton Laboratory

BENE November 2006

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RAL

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

Proton beamFocusing horns

Target

Window

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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

Pulsed proton beam

Vacuum

He @ 1 atm

Window

Graphite target

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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

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

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Helium cooling

He in He out

Titanium - 0.3mm

Titanium -0.3mm

Helium3mm Gap

Upstream

Annulus

Downstream

Helium velocity ≈ 5 m/sHeat transfer coefficient ≈ 150 W/m2K

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Remote handling

Beam Position Monitorchamber

Target station

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Dynamic Stress Analysis

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Transient window temperature

Simulation shows temperature distribution over 5 pulses (15 seconds)

0

50

100

150

200

250

0 5 10 15 20 25 30

Time (s)

Te

mp

(o

C)

Heat transfer coefficient = 140 Wm2/K external and 10 W/m2K internalBeam energy = 50 GeVFrequency = 0.284

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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

-200

-150

-100

-50

0

50

100

150

200

0 1 2 3 4 5

Time from beginning of pulse (μs)

Str

es

s (

MP

a)

Von Mises

Hoop

Longitudinal

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0.3mm Window - Destructive interference

-200

-150

-100

-50

0

50

100

150

200

0 1 2 3 4 5

Time from beginning of pulse (μs)

Str

es

s (

MP

a)

Von Mises

Hoop

Longitudinal

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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 stress3.0 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.

0

100

200

300

400

500

600

0 50000 100000 150000 200000 250000 300000 350000

Heat deposit (J/g)

Pe

ak

str

es

s (

MP

a)

VM centre

Long centre

VM edge

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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 R&D needed for beam power upgrades.

Irradiated material data is crucial. This should be a major research priority in the coming years.

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THANK YOU!

QUESTIONS?