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Tetsuhiko YoritaJASRI/SPring-8 Acc. Div.

SPring-8 Vacuum System

Contents

- Outline of Vacuum system- Pressure behavior- Some topics

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100 mA, 8 GeVCircumference : 1436m, 44 normal cells + 4 Long Straight Sections

Accelerator Complex of SPring-8

Storage Ring

BoosterSynchrotron

Linac

3

e-

length of one cell = 24m (excluding ID) 3 Straight Section Chambers (SC1-3), 2 Bending Magnet Chambers (BM1,2), Absorbers (CR1,2,AB2,3,4)

Normal cell

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Beam Chamber : Ellipse 40mm(vert.)*70mm(hori.)Slot Height : 10mm(14mm) for SC, 12.5mm for BM

Material: Al Alloy A6063-T5 (special extrusion in Ar+O2)

Straight Section ChamberSC1-3

BendingMagnetChamberBM1,2

Chamber cross sectionSC1SC2SC3 BM1BM2

e-

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AbsorbersCR1

CR2

AB3

AB4

AB2 AB1

crotch (CR1,2)

absorber (AB3,4)

crotch(CR1,2) absorber(AB3,4)SR power (100mA) 5.8 kW (370 W/mm2) 4 kW (50 W/mm2)max. temperature 417 oC 215 oC

max. thermal stress 37 kg/mm2 28 kg/mm2

Allowable thermal cycles 7x104 1x106

Material : Glid-Cop

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SC1-3, BM1,2 - Distributed NEG Pump (DNP) *26m (St707/CTAM/30D)

- Distributed Ion Pump (DIP) *5m

CR1,2 & AB3,4 - Lumped NEG Pump (LNP) *4 (St707 WP1250 *20)

- Sputter Ion Pump (SIP) *4

Pumps

LNP

SIP

LNP

pumping speed / cell for CO : 6x103 L/sec

for H2 : 1.6x104 L/sec

DNP

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10-7

10-6

10-5

10-4

10-3

0.1 1 10 100 1000 104

average_ab3 (Pa/A)average_ab4 (Pa/A)average_cr1 (Pa/A)average_cr2 (Pa/A)average_sc1(Pa/A)

ab3ab4cr1cr2sc1

P/I

(P

a/A

)

dose(Ahr)

- P/I decrease with Dx

(x ~ -2/3) - Neither AB nor CR decrease with dose 10~1000 Ahr. - Pressure readings of AB and CR have error due to irradiation. --> BA gauges and cables were shielded.

Pressure rise by SR (P/I) vs. dose

SC1CR1CR2 AB3AB4

8

4 10-9

5 10-9

6 10-9

7 10-9

8 10-9

9 10-9

10-8

2 10-8

3 10-8

4 10-8

0.1 1 10 100 1000 104

TD_normal_ab3 (Pa)TD_normal_ab4 (Pa)TD_normal_cr1 (Pa)TD_normal_cr2 (Pa)TD_normal_sc1 (Pa)

pre

ss

ure

(P

a)

dose(Ahr)

dose(Ahr)Aug/1997:11

1998:661999:2852000:626

2001:10142002:13752003:1769

Beam current = 0mA

Pressure of thermal desorption

NEG reactivation in whole ring - In 1997 (dose 11 Ahr) -->effective - In 1998 (dose 66 Ahr) NEG reactivation in half of ring - In 2001 (dose 1014 Ahr) Recently base pressure is almost constant.

SC1CR1CR2 AB3AB4

9

10-3

10-2

10-1

100

101

102

10-2

10-1

100

101

102

103

104

lifetime*I(Ah)

lifet

ime*

I(A

hr)

dose(Ahr)

Dec/31/1997=29 Ahr /1998=146 /1999=426 /2000=764

/2001=1183 /2002=1578 /2003=1957

NEG reactivation in1997 summer

Replacement of 30mLSS

Replacementof ID17

Lifetime (multi bunch, ID gap : full open)

- Lifetime by gas scattering

> 600 hrs (calculation)

100mA, CO=30%

- Actual Lifetime ~200hrs

lifetime by gas scattering

is not primal.

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Absorber at RF sectionleaked cooling water (gas) There is a possibility thatSR, water and dissolvedoxygen corroded Cu. Normal absorbers arenot so serious,because of different water serieswith less oxygen.

Corrosion with water and SR(RF-AB)

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0.7t

Leakage due to the melting of chamberby aborted electrons

10mm

Injection chamber - narrowest aperture - thin chamber wall of stainless steel - some dispersion at low emi. opt.

Most of aborted electrons hit the wall and melt it

Injection chamber

cross sectionsof chamber wall

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Electro-Magnetic Showerbremsstrahlung e+e- pair creation

&

0.1mm

heat load markis broader thanbeam size of7x290m2

Leakage due to the melting of chamberby aborted electrons (Cont’)

EM shower density depends on Z.

To avoid the melt, electron dumper made of Al with low Z has been installed

cascade of

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Beam Fluctuation

S. Matsui, et al.Jpn. J. Appl. Phys.Vol. 42 (2003) pp.L338

Eddy Current madeby Q-mag. field kicksthe electron beam.

Typical Chamber Vibration (AB2)

Beam Fluctuationdue to Chamber Vibration

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Chamber Vibration @AB2

Beam Fluctuation

Reduction withadditional supports

Beam Fluctuationdue to Chamber Vibration (Cont’)

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Appendix A : ImpedanceBellows and gate valves

- RF finger in bellows CuBe(C1720)

Flange

- RF contact: CuBe(C1720)

Joint part of beam chamber

- Step < 0.5 mm

- Gap < 0.2 mm

Connection between

different cross sections

- Transition angle < 5 ~ 10 deg

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beam size　10x390m2

　　　　　 -->7x290m2

ID section

Appendix B-1:low emittance operationNov. 2002 ~ Oct. 2003Sep. 2005 ~

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IDsection

Appendix B-2:aborted electronbehavior