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Electron Cloud in LHC

Electron Cloud in LHC. V. Baglin. CERN AT-VAC, Geneva. 1. Mecanism and Recipies 2. LHC Vacuum Chambers 3. Diagnostics 4. Conclusions. 1. Mecanism and Recipies. Electron Cloud : the Mecanism

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Electron Cloud in LHC

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  1. Electron Cloud in LHC V. Baglin CERN AT-VAC, Geneva 1. Mecanism and Recipies 2. LHC Vacuum Chambers 3. Diagnostics 4. Conclusions Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  2. 1. Mecanism and Recipies Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  3. Electron Cloud : the Mecanism • In modern machine with dense bunches and large positive current : KEK-B, PEP-II, SPS, RICH, LHC … • Emittance growth, gas desorption and heat load in cryogenic machine • Key parameters : • bunch structure • vacuum chamber dimmension • secondary electron yield • photon electron yield • electron and photon reflectivities • … F. Ruggiero et al., LHC Project Report 188 1998, EPAC 98 Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  4. Electron Cloud : the Recipies • Play with the key parameters • Reduce photoelectron yield (perpendicular vs grazing incidence) • Reduce secondary electron yields (scrubbing, TiZrV coatings, carbon coatings, geometry ..) • Reduce the amount of electrons in the system (solenoid magnetic field, clearing electrodes, material reflectivities …) • Adapt the bunch structure or the chamber geometry to reduce multiplication • … Secondary Electron Yield Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 N. Hilleret et al., LHC Project Report 433 2000, EPAC 00

  5. 2. LHC Vacuum Chambers Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  6. LHC Dipole Vacuum System • Cold bore (CB) at 1.9 K which ensures leak tightness • Beam screen (BS) at 5-20 K which intercepts thermal loads and acts as a screen Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  7. LHC Dipole Vacuum System • Rely on scrubbing at cryogenic temperature • With dense bunch current : kick for high energy electrons ! • But large bunch distances to avoid multiplication : 50 to 75 ns or more Courtesy R. Cimino O. Gröbner. PAC 1997 Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  8. Room Temperature Vacuum System • ~ 1 μm thick, Non Evaporable Getter TiZrV coated vacuum chambers ensure the required vacuum performances for LHC • Some vacuum chambers were constructed and getter coated … Courtesy R.Veness AT/VAC and P. Chiggiato TS-MME Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  9. Room Temperature Vacuum System • ….. and installed inside the LHC tunnel Collimators Warm magnets Vacuum chambers Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  10. TiZrV Vacuum Performances ESD Yields Pumping Speed PSD Yields Courtesy P. Chiggiato TS/MME C. Benvenuti et al. J.Vac.Sci.Technol A 16(1) 1998 Secondary Electron Yield V. Anashinet al. EPAC 2002 Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 C. Scheuerlein et al. Appl.Surf.Sci 172(2001)

  11. Room Temperature Vacuum System : Demonstration Ultimate Vacuum Pressure Distribution after NEG Activation of the LHC Room Temparture Vacuum Sectors G. Bregliozzi et al.EPAC’08, Genoa 2008 Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  12. 3. Diagnostics Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  13. Vacuum Gauges Courtesy J.M. Jimenez Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  14. Vacuum Gauges Courtesy J.M. Jimenez Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  15. Current measurements Courtesy J.M. Jimenez Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  16. Current measurements Courtesy J.M. Jimenez Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  17. Current measurements Courtesy J.M. Laurent Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  18. Heat Load Measurements V. Baglin. APC, 26/5/2005 Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  19. Heat Load Measurements Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  20. Pilot Sectors • Under definition .. G. Bregliozzi et al.EPAC’08, Genoa 2008 Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  21. 4. Conclusions Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  22. After repair of sector 3-4 ….. Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  23. And successfull operation with beam ….. Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  24. HIGGS BOSON DISCOVERY • Followed by … … P. Higgs in the CCC Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

  25. Electron Cloud could show up ! We are waiting for it ! Meanwhile we (continue) to prepare ourselves Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

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