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Upgrade Plan of KEKB Vacuum system

Upgrade Plan of KEKB Vacuum system. Y. Suetsugu KEKB Vacuum Group. Contents. Challenges for vacuum system Designs for key issues Beam ducts, Flanges, RF-shielding, Cures for ECI,, Remained issues Technical General Summary. Challenges for vacuum system.

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Upgrade Plan of KEKB Vacuum system

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  1. Upgrade Plan of KEKB Vacuum system Y. Suetsugu KEKB Vacuum Group Contents • Challenges for vacuum system • Designs for key issues • Beam ducts, Flanges, • RF-shielding, Cures for ECI,, • Remained issues • Technical • General • Summary Pre-kickoff Meeting @ KEK

  2. Challenges for vacuum system Key parameters for vacuum system: • High current (LER:9.4 A, HER:4.1 A) • Short bunch (sz = 3 mm) • Intense SR power • Max. power density of 28 kW/m (40 W/mm2) even a half aperture of 110 mm, for example. • High photon density • Photon density ~1x1019 photons/m/s in average • Large gas desorption • Gas load ~ 5x10-8 Pa m3/s/m (forh = 1x10-6 molecules/photon) • Average pressure ~ 5x10-7 Pa for S ~ 0.1 m3/s/m • Electron Cloud Instability (ECI) becomes a big issue in positron ring • Intense HOM(higher order mode) power • For a loss factor of 1 V/pC, loss power ~ 200 kW Pre-kickoff Meeting @ KEK

  3. Present designs for key items • We have been developing key components and techniques to tackle these issues. • Beam duct • Copper beam duct with ante-chambers  Low SR power • Pumping system • Distributed pumping scheme  Effective pumping • Connection flange • Special MO-type flange  Secure RF bridge • RF shielding of bellows and gate-valves • Comb-type RFshield basically  Secure RF shield • Movable mask (collimator) • Stealth type (still under study)  Low impedance • Cures for ECI • TiN coating or (groove)  Low secondary electron yield • Clearing electrode  Direct elimination of electros Low Impedance Little photoelectron Pre-kickoff Meeting @ KEK

  4. Beam duct • Copper beam duct with ante-chambers • Copper is required to withstand intense SR power • Features (compared to simple pipe): • Low SR power density • Low photoelectrons in beam pipe • Low beam impedance • Expensive Pump Beam SR HER LER (f90) Pre-kickoff Meeting @ KEK

  5. Beam duct • Several test ducts have been installed in KEKB positron ring. • Reduction of photoelectrons was confirmed. • All ducts at arc section should be replaced. Electron numbers Straight duct ~3.6 m -30 V Circular duct 1/1284/3.77 Q-duct with BPM Duct with ante-chamber f 90 mm Pre-kickoff Meeting @ KEK

  6. Beam duct Bent duct for LER (f 90 mm) Slit for pump channel 2008.03.19 Bending and installation of slits are now under study Pre-kickoff Meeting @ KEK 6

  7. Distributed pumping system • Multilayer NEG strips in an antechamber • Increase capacity and pumping speed • Small impedance if set in an ante-chamber • Auxiliary pump: Sputter ion pump Pump Multilayer NEG strips for test (three layers) SR 12 mm Prot-type: ST-707 strip Three layers Indirect heating 1 m Heaters Pre-kickoff Meeting @ KEK

  8. Connection flange • Special MO-type flange for a beam duct with ante-chambers. • Features (Compared to usual one): • No gap inside • Sure RF bridge • Applicable to a complex aperture • Simple structure • Already applied to test beam ducts and bellows with ante-chambers. MO-type flange for bellows MO-type flange for beam duct Pre-kickoff Meeting @ KEK

  9. RF shielding Comb-type RF-shield • Comb-type RFshield • Features (compared to finger type): • Low beam impedance • High thermal strength • Applicable to complex aperture • Little flexibility (offset) • Effect of RF shielding was demonstrated in KEKB. • Finger-type as an option • If more flexibility is required. Temperature of bellows Without cooling fan Pre-kickoff Meeting @ KEK

  10. RF shielding • Already applied to bellows chambers and gate-valves, with an aperture of beam duct with ante-chambers. • They have been installed into KEKB and tested. Bellows chamber Gate-valve Pre-kickoff Meeting @ KEK

  11. Movable mask (collimator) • Big impedance sources in the ring • Planning to use “stealth” type (Ver.6) • Low beam impedance • Present Ver.4 ~ 1V/pC (f 90 mm) 200 kW power loss • Loss factor decreases to ~1/10(f 90 mm). • Manageable by conventional HOM absorber Loss factor Ver.4 Ver.4 Loss factor [V/pC] Ver.6 Ver.6 Bunch length [mm] Pre-kickoff Meeting @ KEK

  12. Movable mask (collimator) • Trial models were installed and tested with beam. • Principle was proved experimentally. • Temperature rise of bellows decreased to 1/2 ~ 1/3. • But, could not withstand a high intensity beam yet. • Start with Ver.4 ? • While beam current is low. Temperature of bellows near masks Head of Ver.6 (trial model) Beam Head Support Pre-kickoff Meeting @ KEK

  13. Cure for ECI_1 • A critical issue for positron ring • TiN coating on inner surface • Decrease secondary electron yield (SEY): Max. SEY ~0.9 • A test stand for the coating was built in KEK, and applied to a test duct with ante-chambers. • Decrease of electrons at high current region was demonstrated. Electron numbers ~4 m f 90 mm Pre-kickoff Meeting @ KEK

  14. Cure for ECI_2 • Clearing Electrode • A possible measure even inside of magnet • An electrode for test with a low beam impedance was developed, and tested. • The principle was proved experimentally. • Electrons decreased to ~ 1/10 by applying 500 V. • Under study • Grooves will be also tested. Electron numbers Clearing electrode for test Electron Current [A] Head -500V 0V +500V Applied voltage [V] Pre-kickoff Meeting @ KEK

  15. Remained issues _ Technical • Optimization of beam duct shape • CSR (Coherent Synchrotron Radiation) problem have a great effect on the luminosity. • Deformation of beam duct by heating • Displacement gauge for every BPM? Larger aperture  ---- Smaller aperture Low impedance Cure for CSR (ex, resistive wall) [Low cost?] Effective pumping (f 50) (f 90) ? Pre-kickoff Meeting @ KEK

  16. Remained issues _ Technical • Required pressure • Now 5x10-7 Pa is a goal. • First Ion Instability require lower pressure in a simulation, ~1x10-7 Pa for example. • More pumps? • Cures for ECI in magnet • Still studies are undergoing. • Clearing electrode ? Grooves? Only TiN? • Drift space: TiN coating + Solenoid will be OK. • Design of special components • Septum, Abort window, HOM absorber, Cross section, … • Design of vacuum system at IR. • IR optics is still floating. • How to keep sufficient aperture, how to deal intense SR,, Pre-kickoff Meeting @ KEK

  17. Remained issues _ General • Cost • Vacuum components are more complicated than those of other machine to achieve high current, i.e., Luminosity. • Possibility of cost-reduction are continuously considered, such as to use aluminum duct for weak SR sections (with copper SR crotch?). • Vendor • Manufacture ~2000 copper beam ducts ( 2 ~ 6 m long) in 3 years! • Find available vendors widely, all over the world. • Some R&D were performed with BINP, for example. • Installation • Install ~2000 beam ducts and bellows in 2 years! • Stored place, Installation procedure, Preparation process,, • Man power Pre-kickoff Meeting @ KEK

  18. Summary • Upgrade of KEKB is a great challenge for the vacuum system. • R&Dshave been performed for these years, and basic designs of key vacuum components is near completion. • But, various practical problems are still remained. • Any solutions should be found in this one year. • We will appreciate your corporation. 2008.03.19 Pre-kickoff Meeting @ KEK 18

  19. Pre-kickoff Meeting @ KEK

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