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

F. Ruggiero et al., LHC Project Report , EPAC 98 Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 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 …

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 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 N. Hilleret et al., LHC Project Report , EPAC 00

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

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 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 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 O. Gröbner. PAC 1997 Courtesy R. Cimino

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

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

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 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 Diagnostics

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

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

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

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

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

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

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

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

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

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

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

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

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