1. 1 Tetsuhiko Yorita JASRI/SPring-8 Acc. Div. SPring-8 Vacuum System Contents - Outline of Vacuum system - Pressure behavior - Some topics

2. 2 100 mA, 8 GeV Circumference : 1436m, 44 normal cells + 4 Long Straight Sections Accelerator Complex of SPring-8 Storage Ring Booster Synchrotron Linac

3. 3 e-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

4. 4 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+O 2 ) Straight Section Chamber SC1-3 Bending Magnet Chamber BM1,2 Chamber cross section SC1 SC2 SC3BM1BM2 e-e-

5. 5 Absorbers CR1 CR2 AB3 AB4 AB2AB1 crotch (CR1,2) absorber (AB3,4)

6. 6 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 : 6x10 3 L/sec for H 2 : 1.6x10 4 L/sec DNP

7. 7 -  P/I decrease with D x (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 SC1CR1CR2AB3AB4

8. 8 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. SC1CR1CR2AB3AB4

9. 9 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.

10. 10 Absorber at RF section leaked cooling water (gas) There is a possibility that SR, water and dissolved oxygen corroded Cu. Normal absorbers are not so serious, because of different water series with less oxygen. Corrosion with water and SR(RF-AB)

11. 11 0.7t Leakage due to the melting of chamber by 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 sections of chamber wall

12. 12 Electro-Magnetic Shower bremsstrahlunge+e- pair creation & 0.1mm heat load mark is broader than beam size of 7x290  m 2 Leakage due to the melting of chamber by 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

13. 13 Beam Fluctuation S. Matsui, et al. Jpn. J. Appl. Phys. Vol. 42 (2003) pp.L338 Eddy Current made by Q-mag. field kicks the electron beam. Typical Chamber Vibration (AB2) Beam Fluctuation due to Chamber Vibration

14. 14 Chamber Vibration @AB2 Beam Fluctuation Reduction with additional supports Beam Fluctuation due to Chamber Vibration (Cont’)

15. 15 Appendix A : Impedance Bellows 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

16. 16 beam size 10x390  m 2 -->7x290  m 2 ID section Appendix B-1: low emittance operation Nov. 2002 ~ Oct. 2003 Sep. 2005 ~

17. 17 ID section Appendix B-2: aborted electron behavior