The straight vacuum chambers of the SRRC 1.3 GeV electron storage ring

Vacuum~volume44/numbers 5-7/pages 545 to 548/1993

0042-207X/9356 00+ O0 © 1993 Pergamon Press Ltd

Printed m Great Bntam

The straight vacuum chambers of the SRRC 1.3 GeV electron storage ring J R C h e n * a n d Y C L i u t , Synchrotron Radmtlon Research Center, No 1 R & D Road VI, Hsinchu Scmnce-Based Industrml Park, Hsmchu 30077, Talwan, ROC

The stratght vacuum chambers (S-chamber) of the SRRC 1 3 GeV electron storage ring are destgned, fabricated a~d tested Vacuum pipes, bellows, flanges, pumping ports and most of the other components are made of aluminum The S-chambers are designed to have the function of reducing radto-frequency (rf) impedance and remowng the heat created by synchrotron radmt/on A stringent tungsten-inert gas (TIG) welding process ts performed to minimize the deformations m both longitudinal and transverse dffections. In order to achmve uhv, in sltu bakeout by tape heaters ts adopted The testing results showed that the designs for remowng the bakingrelated problems work well

I~ Introduction Due to its high thermal conductivity, easy machining, low outgassing rate, low residual radioactivity and other benefits, alumir~um is chosen as the vacuum chamber material of the 1 3 GeV ekctron storage ring of the Synchrotron Radiation Research C~nter (SRRC) in Talwan ' 4 Many criteria must be considered when designing chambers of aa electron storage ring 5 8 Considerations for ultra-high vacuum (tahv), deformation, rf impedance, heat removal, rigidity or ttexlbillty of supporting frame and other requirements must be met in order to get a reliable storage ring Basically, there are two kinds of vacuum chambers, bending (B-) and straight (S-), of the SRRC vacuum system The Bchamber has been described previously 9 In this paper, the aluminum pipe, heat absorber, rfimpedance, welding and system test of the S-chamber are described 2. Design and fabrication On) Aluminum pipe. The aluminum pipe is made of the aluminum alloy A6063-T4 (A1-Mg-SI alloy) by the extrusion method The tuner cross section of the pipe is an ellipse of 80 mm width and 38 mm height (Figure l) Two cooling channels (one is a dummy) on the opposite sides of the beam duct are designed for the purpose of keeping symmetry In order to check the dimension, to Support and align the chamber dunng welding and/or installation process, the flat outside region around the cooling channels is also designed In addition to the dimension tolerance to the beam duct cross section, a straightness of < + 0 15 mm m - ~ is also reqmred for ~he extruded pipes Distributions of four important dimensions of the extruded pipe are shown In Figure 2(a)-(d) A chemical cleaning process is adopted to treat the aluminum surface after machining However, some of the pipes are

The authors are also affiliatedto *Institute of Nuclear Science,tDepartinent of Physics,National Tsmg-Hua Umverslty,Hsinchu 30043,Taiwan, ROC

machined by an oil-less process (with ethyl alcohol) For these chambers, no chemical treatment IS required after machining Packaging is carried out carefully by using dry N : gas purging and deoxidizer and desiccant in an aluminum-polymer bag during transportation and in storage (b) Cooling channel and heat absorber. Due to the high thermal conductivity of aluminum, the synchrotron radiation power on the chamber is easily removed by a co-extruded cooling channel at one side of the beam duct To prevent water leakage in a vacuum, there is no penetration of the cooling pipe into the vacuum Although the hnear heat density on the straight chamber is not so high (max < 10 W c m - ' , average ~<1 W cm-~), a special radmtlon absorber is necessary to shadow the components without cooling channel, e g bellows, sector gate valve and ceramic chamber Absorbers for these components are made by welding filler (aluminum alloy A4043), which melts together with the beam duct to get a good thermal contact The absorber has enough height to shadow the component from the shining of synchrotron light, and at least 2 mm more is added to the height of absorber to account for the alignment error and beam orbit distortion

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Figure 1 Cross section of the elhptlcal pipe of S-chamber 545

J R Chen and Y C Ltu The strmght vacuum chambers of the SRRC

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Figure 2. Four important dimension distributions of the extruded elhptlcal pipe (a) Width, (b) height, (c) straightness and (d) height offiduclal region

In a d d l h o n to absorbers, thermocouples are attached at the d o w n s t r e a m side of some s h a d o w e d c o m p o n e n t s These thermocouples form part of the interlock system o f the m a c h i n e (e) Rf impedance. In order to reduce the t / mapedance of the v a c u u m c h a m b e r , the beam duct cross section must be kept as s m o o t h as possible Nevertheless, d l s c o n t l n m t y can not be fully avoided in some c o m p o n e n t s , such as the bellows, sector gate valve, p u m p i n g port, m o n i t o r , flange gap a n d some special pieces o f S - c h a m b e r Several solutions, such as a transition piece, t / bridge a n d a small slots design, are considered m the S - c h a m b e r for reducing r/impedance A transition piece is used to make a connection between two c h a m b e r s with different cross sections, e g the t r a n s m o n from a n elliptical to a circular pipe The m a x i m u m angle o f the changing slope of the t r a n s m o n piece is kept ~<20 Three designs o f rJ bridge are used in bellows, sector gate valve a n d flange gap, respectwely Inside of the bellows, an rf bridge with CuBe sliding fingers is equipped The contact force of each sliding finger is > 100 g F o r a sector gate valve, a n r! bridge across the cawty of the gate valve is attached in order to m a k e an ~[ contact between two opposite flanges of the gate valve The flange aperture o f the gate valve is designed to have the ~ame dimension as t h a t o f the elhptical cross section of b e a m duct The small cavity formed in a sealed conflat-flange pair would also induce r! impedance A piece o f a l u m i n u m plate with an elhptlcal aperture (38 x 80 m m a n d thickness 2 2 m m ) IS fixed to one flange of the flange-pair ( h g u r e 3) In order to reduce r! impedance Figure 4 shows the schematics o f the p u m p i n g port c h a m b e r Instead of using a big hole with larger conductance, m a n y holes are m a c h i n e d in the elhptical a l u m i n u m pipe m order to reduce the r f l m p e d a n c e o f the p u m p i n g port F o r pressure monitoring, Ionization gauges are put at the position t h a t a direct hne of sight is impossible between electron b e a m a n d the gauge Moreover, a 'plug' with m a n y small holes is put lnbetween the gauge and the beam duct in order to shield the r! wave Into the gauge 546

(d) Welding. A typical S - c h a m b e r is s h o w n n! Figure 5 In this chamber, there are vacuum pipes, flanges (FL, x 2), bellows (BL, x 2) p u m p ports (PT, x 2), b e a m position m o n i t o r s (BPM, x 2) and c o o h n g pipes All the c o m p o n e n t s are m a d e o f a l u m i n u m and IOlnted together by T I G welding to form a n S - c h a m b c r Basically there are six kinds of weldlngs in this c h a m b e r the lOlnlngs between the elliptical b e a m pipe a n d c o m p o n e n t , between the cooling pipe a n d beam pipe between a small plug at cooling channel and the b e a m pipe, between the circular pipe (outer d i a m e t e r 0160 into) a n d the flange o f p u m p i n g port and between the circular pipe a n d the p e n e t r a t i n g elliptical beam duct of p u m p i n g port F o u r criteria are introduced to the welding of a S-chamber, leak rate < 2 x 10 )° atm-cc s ~, stratghtness < I m m m ~ in b o t h horizontal a n d vertical directions, length deviation to bc within + I 0 2 0 m m (this value depends on the length o f the S-chamber), a n d small relative r o t a t i o n of two BPMs (max < 0 2 m m to the b e a m axis) A typical process of the S - c h a m b e r fabrication IS listed by stcps m Table I Before welding for the elhptlcal pipes, the c o m p o n e n t s

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J R Chen and Y C Ltu The straight vacuum chambers of the SRRC

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Figure 5. Schematics of a typical S-chamber, the number shown in the figure is the sequence of elliptical welding FL flange, BL bellows, IIPM beam position monitor, PT pump port

Figure 6. The welding sequence for the joining between the elhptlcal pipe and the orcular pipe of pumping port are p r e p a r e d a n d inspected F o r the p u m p i n g port welding, which is one of the most p r o b a b l e d e f o r m a t m n sources, a symmetric welding (Figure 6) is performed in order to reduce the deformation caused by welding The welding for elliptical pipes is performed in sequence as s h o w n in the n u m b e r s of Figure 5 A t the beginning, small c o m p o n e n t s are welded together to form a longer piece (sub-chamber) These longer pieces are then p u t In a long r o t a t a b l e welding b e n c h to form a complete S-chamber Before the final welding, a careful dimension check (for straightrtcss a n d length) is performed, so t h a t the d e f o r m a t i o n after the final welding is within the designed tolerance Practical experiences for the welding d e f o r m a t i o n of the Sc h a m b e r o f this work are 0 3q3 5 m m shrinkage in length for each elliptical welding a n d ~<0 5 m m m i d e f o r m a t i o n in vertical a n d horizontal directions B o t h values are considered in the comp o n e n t p r e p a r a t i o n a n d the welding of a n S - c h a m b e r

3. System test One sextant o f the S R R C ring v a c u u m system has been fabricated a n d tested In this sextant, there were three bending c h a m b e r s

4. Summary

Table 1. S-chamber fabrication process ~luence

Process Drawmg check Component fabrication Component inspection Pumping port fabrication and check Sub-chamber welding Alignment and welding of sub-chamber pieces to form a S-chamber Dimension check

Leak check

a n d seven straight c h a m b e r s In the system, a l u m i n u m flange sealing by using a l u m i n u m gaskets a n d a l u m i n u m bolts a n d nuts were a d o p t e d Oil-less t u r b o m o l e c u l a r p u m p systems were used for the evacuation d u r i n g r o u g h i n g a n d tn sttu b a k i n g processes Tape heaters were used to bake the c h a m b e r a n d c o m p o n e n t s After baking, p u m p i n g was t a k e n over by n o n - e v a p o r a b l e getters a n d sputter ion p u m p s A pressure o f < 1 × 10 10 t o r t was reached after b a k i n g at ~ 140°C for 24 h In addition to the v a c u u m pressure, the d e f o r m a t i o n a n d displacement o f the v a c u u m c o m p o n e n t s are also i m p o r t a n t factors to be tested T h e longitudinal displacement o f the fixed point, mainly at the location o f BPM, was observed to be ~<0 1 m m during b a k e o u t The displacement recovered to < 0 05 m m after having cooled d o w n to r o o m t e m p e r a t u r e T h e value o f transverse displacement was a b o u t two times lower t h a n t h a t of the longitudinal displacement F o r heavy ion p u m p s in the S - c h a m b e r region, spring supports are designed to decrease the load on flange seahng during b a k e o u t This flexible s u p p o r t functioned as well as was expected

Remark BPM, bellows, Al-pipe machining, cleaning Dimension check, visual check, leak check BPM cahbratlon Straightness < + 0 5 mm m - i (before welding) Straightness < + 1 mm m ~, length deviation < + 1 0~2 0 mm, BPM rotation < 0 2 mm Leak rate < 2 x 10- L0atm CC S - t

The S-chambers o f the S R R C v a c u u m system are designed, fabricated a n d tested The dimensions of the c o m p o n e n t s are carefully checked R a d i a t i o n absorbers are designed for the comp o n e n t s which have no cooling channel R f l m p e d a n c e is reduced by the design of r f bridges a n d small hole ports A stringent welding process is performed so t h a t the u h v a n d dimension criteria are met for S-chambers A sextant ring v a c u u m system was installed, a n d a pressure of < 1 x l0 ~0 torr was reached after b a k i n g at ~ 140°C for one day The s u p p o r t i n g frames of the S-chambers were suitable to reduce the b a k i n g related displacement

Acknowledgements The a u t h o r s would like to t h a n k their colleagues o f the S R R C v a c u u m g r o u p for their contributions, a n d would also like to 547

J R Chen and Y C Llu ThestralghtvacuumchambersoftheSRRC

thank Professor H Ishlmaru o f K E K for his many suggestions regarding the aluminum system

References H lshlmaru, J Vac Set Tethnol A2(2), 1170 (1984)

2j R Chen, K Narushlma and H Ishlmaru, J V(I( S~t Te~hmd, A3(6) 2188 (1985) ~M Suemltsu, T Kaneko and N Mlyamoto J Va~ S~I Technol, AS(1), ~7 (1986)

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4j R Chen, G Y Hslung D C ('hen D J Wang, G S Chen and Y ( Lm Pr~;~ Topical Conf Vacuum Deszqn o[ Advanced and Compact Svnchrotrml Ltqht Source~, BNL, New York, 16 18 May (1988) ! Kouptstdls and A G Mathewson DESY Report, DESY 76/49 (1976) ~'A G Mathewson and G Honkoshl, KEK Report, KFK-78-9 (19781 - I Le Duff ,¥u~ l lmtrum ~leth A239, 83 (1985) sS Krmsky, BNL Report, BNL 23749 (1977) "J R Chen, G S Chen, D J Wang G Y Hslung and Y C Llu, Vacuum 41(7 9) 2079 (1990)