matt rooney ral the t2k beam window matt rooney rutherford appleton laboratory bene november 2006

Matt Rooney

RAL

The T2K Beam Window

Matt RooneyRutherford Appleton Laboratory

BENE November 2006

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

Matt Rooney

RAL

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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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

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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.

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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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RAL

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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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!

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RAL

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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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.

Matt Rooney

RAL

THANK YOU!

QUESTIONS?