The Current T2K Beam Window

Design and Upgrade

Potential

Oxford-Princeton Targetry Workshop

Princeton, Nov 2008Matt Rooney

T2K Target Station

Proton beamFocusing horns

Target

Window

Beam window design overview

Exploded assembly view

Side plates-Provide a firm support for the beam window and guidance during installation

Top plate- Used for inserting and removing window- Protects pillow seals and mating flanges- Provides a connection point for services

Inflatable seals-Seal helium vessel and beam line

Ti-6Al-4V beam window

Ti-6Al-4V Beam window

- Some difficulties with post-machining and post-weld distortion – a common problem with Ti-6Al-4V.- E-beam welding conducted by Culham UKAEA Special Techniques Group.

Helium cooling

He in He out

Titanium - 0.3mm

Titanium -0.3mm

Helium3mm Gap

Upstream

He gap

Downstream

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

Helium flow grooves

He in He out

Inflatable seals

Picture courtesy of Y. Miyake andS. Makimura (KEK)

Picture courtesy of PSI

PSI

KEK Muon Group

Pillow seals

outer diaphragm

inner diaphragm

bellows

Pictures courtesy of Y. Miyake (KEK)

pressure line

vacuum line

~ 200 mm

Window – side viewSection view

KEK Muon Group pillow seal

Seal and mating flange

Seal foils (surface roughness, Ra = 0.004 µm, Rt = 0.030 µm)

Polished flange (surface roughness, Ra = 0.020 µm)

Seals manufactured by UHV Design in UK.Developed from similar design at KEK (via Oak Ridge via PSI).

Assembled Window

Remote Handling

Remote handling

MonitorChamber(Canada)

Target Station(Japan)

Remote installation

Stress analysis and upgrade potential

Beam properties

0

1E+14

2E+14

3E+14

4E+14

5E+14

6E+14

7E+14

8E+14

9E+14

0 0.005 0.01 0.015 0.02

Radius (m)

Hea

t (J

/m2)

- 0.75 MW beam power- 3.3 x 1014 protons per pulse- Gaussian profile with 4 mm rad rms beam spot- 5 µs pulse = 8 x 58ns bunches- 1 pulse every 2 seconds at 30 GeV

Energy deposited in window with distance from beam centre

ANSYS Static Stress Results

UTS Ti-6Al-4V ≈ 1GPa

NOTE: 100W/m2K heat transfer coefficient applied to internal wall

Stresses at Centre of 150mm Diameter Hemisphere

0

20

40

60

80

100

120

140

0 0.2 0.4 0.6 0.8 1

Thickness at Beam Centre (mm)

Vo

n M

ise

s S

tre

ss

(M

Pa

)

0

100

200

300

400

Te

mp

era

ture

(o

C)

Thermal Stress

Pressure Stress

Combined Stress

Temperature

0

10

20

30

40

50

60

70

80

90

0 5 10 15 20 25 30

Time (s)

VM

str

es

s (

MP

a)

Inner edge

Outer edge

Centre

-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

Transient thermal stress over multiple pulses

Stress waves developing over pulse

Ti-6Al-4V – the good news

0

100

200

300

400

500

600

700

800

900

1000

0.E+00 1.E+06 2.E+06 3.E+06 4.E+06 5.E+06 6.E+06 7.E+06 8.E+06 9.E+06

Number of cycles

Ma

xim

um

str

es

s (

MP

a)

Fatigue strength

Stress @ 0.75 MW

Safety factor of 4-5

Yield strength

Ti-6Al-4V – the bad news

- reduction in strength at elevated temperatures

T2K beam window upgrade potential

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

Stress Analysis Overview

- Long term survival of window looks likely for 0.75 MW beam.- Beam upgrades with increased PPP would test the limits of the material.- Potential for power upgrades more promising if number of pulses is increased. - Radiation damage then becomes the dominant factor in determining live in service.

Fin