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

AbV-4 AbH-3 AbH-2 AbV-1 AbV-7 AbH-6 AbV-5 X、Y X、Y、Z X、Y X、Y、Z X、Y SSRF X、Y、Z X、Y 3

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 beneath the photon stops pumps are located

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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.m

3 /s/m 2 Sufficient mechanical strength Deformation for BPM Flatness

＜

0.5 mm Roughness

＜

0.8

μ

m

＜

0.03mm

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 Sample

Element 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 A2 Region: Sur Technique:XPS Source:Mg K-Alpha Analyser:CAE=100 Step=0.50

180.0k

160.0k

140.0k

120.0k

100.0k

80.0k

60.0k

40.0k

20.0k

0.0

0 100 200 300 400 500 600 700

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

Upper piece Welding edge Slot Lower piece Alumimum tube Welding edge Groove Chamber body SSRF 23

Welding Platform

Clamp Wedge Upper piece of chamber Welding edge Support Bolt Clamp Lower piece of chamber Bolt Support Flatform SSRF 24

TIG Welding for Chamber

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Crack

Welding Crack

Stainless steel（316L） Alumunum alloy（6061） Prolonging pipe（6061） SSRF Chamber（5083） 26

Dimensional Inspection

• • • •

Flatness (upper surface) 0.23 mm (bottom surface) Max. deformation in vacuum load 0.48 mm Max. error in transverse direction 1.4 mm Surface roughness (beam chamber) 0.25-0.61

μ

m (antechamber) 0.28-0.80

μ

m 0.28 mm

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Max. Error in Transverse Direction

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Vacuum Test Results

• • • •

Total leak rate

（

Pa.m

Ultimate pressure

（

Pa 3 /s

） ）

Outgassing rate

（

Pa.m

3 /s/m 2

） ＜

4.0

×

10 -10 4.9

×

10 -9 1.7

×

10 -8 4.1

×

10 -10 RGA spectrum No contamination peak in 10 -10 Pa

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Pumping Down Curve

1E-5 1E-6 1E-7 1E-8 1E-9 150¡æBake out Start SIP Stop bake out Degas Room temperature P1 P2 P3 TSP Degas+sublimation 1E-10 1E-11 0 12 24 36 48 60 TSP sublimation 72 84 96 time (hours) 108 120 132 144 156 168 SSRF 30

Conclusion

• • • •

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

Many effects have corresponding problems.

been taken to A lot of experiences have been accumulated.

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

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6m-long Chamber Prototype

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