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ALUMINUM ALLOY VACUUM CHAMBERS FOR SSRF

L.X. Yin, D.K. Jiang, H.W. Du, X.L. Jiang

SSRF Vacuum Group

Shanghai National Synchrotron Radiation Center

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CONTENTS

• Outline of SSRF vacuum system

• Aluminum Vacuum Chambers– Design

– Fabrication of prototype

– Test

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Vacuum System Structure

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Principle of Vacuum System Design

• Antechamber type structure

• Machined and welded aluminum alloy vacuum chambers

• SR photons are intercepted by OFHC photon stops except to beamline

• SR irradiate the photon stop surface in 10°angle

• Titanium sublimation pumps are located beneath the photon stops

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Vacuum System Model

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History of Aluminum Chambers

• Early 1970s Extrusion SPEAR, PF

• End of 1980s Antechamber extrusion SPring8, APS

• End of 1980s Machining + welding– Machining upper and lower

halves out of aluminum plate and welding at the periphery

ALS, PLS, SSRC

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Requirements for SSRF Chambers

• A clean inner surface

q ＜ 6.7×10-10 Pa.m3/s/m2 • Sufficient mechanical strength

Deformation for BPM ＜ 0.03mm

• Flatness ＜ 0.5 mm • Roughness ＜ 0.8 μm• Fit relative systems

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Materials

• Aluminum alloy A5083-H321. – Nonheat treatable aluminum-magnesium alloy

– A small amount of cold work

– Stretched and stabilized

– Good weldability and dimensional stability

• SS316L--A6061-T6 explosion bonded plates

– Checked by ultrasonic detector

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Structural Design

• Different features on the external surface

• Support stages inside the chamber

• Enough space between the chamber and the magnets

• Conflat® Flange with AL-SS transition material

• Helicoflex® gaskets on BPM flanges

• Helicoil® screws inside the screw holes

• High precision holes for survey

• Water-cooling channels in the chamber body

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Chamber Structure (1)

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Chamber Structure (2)

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BM and Chamber

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QM and Chamber

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SM and Chamber

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RF Shielded Flange

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1m-long Chamber model

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Machining

• Numerically controlled mill• Dedicated milling cutters• Water soluble metalworking fluid• Spray cooling method• No polish by sandpaper• Constant temperature workshop

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Machining Procedure

• Chamber piece– Blank the plate

– Machine and weld the water - cooling channel

– Rough machine the features

– Release and keep free

– Finish machine in two steps

• BPM hole– Rough machine

– Assemble the two halves

– Finish machine both of the BPM holes

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Numerically controlled milling

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Cleaning

• Purpose– Clean surface contamination

– Eliminate the old surface layer

– Form a new surface layer

• Procedure– Scrub, ALMECO 18, room temperature

– Scrub, CITRANOX, room temperature

– Scrub, ALMECO 18, 50 - 60℃– Rinse, distilled water

– Dry, room temperature

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XPS Test for SampleElement C O Al Oxide layer thickness

Before clean 68.4% 23.6% 8.0%

After clean 23.6% 71.2% 5.2% 61.7 Å

0 100 200 300 400 500 600 700 800 900 1000 11000.0

20.0k

40.0k

60.0k

80.0k

100.0k

120.0k

140.0k

160.0k

180.0k

A2 Region: SurTechnique:XPS Source:Mg K-AlphaAnalyser:CAE=100 Step=0.50

Rel

ativ

e in

ten

sity

(c/

s)

BINDING ENERGY (eV)

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Welding

• AC TIG welding with filler• Hand hold• Surface protection from any contamination• Humidity control in workshop• Remove oxide layer • Argon gas flowing inside chamber

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Welding Structure Design

Welding edge

Slot

Lower piece

Upper piece

Groove

Welding edge

Chamber body

Alumimum tube

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Welding Platform

Upper piece of chamber

Lower piece of chamber

Bolt

Support

Clamp

Wedge

Flatform

Support

Bolt

Welding edgeClamp

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TIG Welding for Chamber

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Welding Crack

Prolonging pipe 6061（ ）Crack

Chamber 5083（ ）

Alumunum alloy 6061（ ）

Stainless steel 316L（ ）

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Dimensional Inspection

• Flatness (upper surface) 0.23 mm

(bottom surface) 0.48 mm• Max. error in transverse direction 1.4 mm • Surface roughness (beam chamber) 0.25-0.61μm

(antechamber) 0.28-0.80μm• Max. deformation in vacuum load 0.28 mm

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Max. Error in Transverse Direction

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Vacuum Test Results

• Total leak rate （ Pa.m3/s ） ＜ 4.0×10-

10

• Ultimate pressure （ Pa ） 4.9×10-9

1.7×10-8

• Outgassing rate （ Pa.m3/s/m2 ） 4.1×10-1

0

• RGA spectrum

No contamination peak in 10-10 Pa

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Pumping Down Curve

0 12 24 36 48 60 72 84 96 108 120 132 144 156 1681E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

Degas

TSP sublimation

TSP Degas+sublimation

Room temperature

Stop bake out

Start SIP

150¡æBake out P1 P2 P3

Pre

ssur

e (

Tor

r)

time (hours)

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Conclusion

• A complete process for the chamber prototype manufacture has been performed with acceptable dimensional accuracy and good vacuum properties.

• Many effects have been taken to solve corresponding problems.

• A lot of experiences have been accumulated.

• The large aluminum alloy UHV chamber for SSRF can be manufactured on domestic technology.

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6m-long Chamber Prototype