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

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

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 -  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 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 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 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 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 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 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 Chamber Beam Fluctuation Reduction with additional supports Beam Fluctuation due to Chamber Vibration (Cont’)

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

17 ID section Appendix B-2: aborted electron behavior