1. CERN F. Ruggiero Univ. “La Sapienza”, Rome, 20–24 March 2006 Measurements, ideas, curiosities fundamental limitations to the ultimate performance of high-luminosity colliders Complement to the lecture on Electron Cloud and Beam-Beam Effects Electron Cloud and Beam-Beam Effects

2. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects Electron Cloud build-up and Le Châtelier’s principle Henri Louis Le Châtelier (1850-1936) was a French industrial chemist. In 1888 he made a remarkable observation: Henri Le Châtelier A man of Principle… In modern accelerators we want to accumulate more and more intense, positive beams. Nature reacts by the fast build-up of negative electron clouds that tend to neutralize the system! "If a dynamic equilibrium is disturbed by changing some conditions, the position of equilibrium moves to counteract the change."

3. 3 blue: e-cloud effect observed red: planned accelerators longer fewer more intense bunches more ‘ultimate’ bunches Scaling of electron cloud effects experience at several storage rings suggests that the e-cloud threshold scales as N b ~  t sep possible LHC upgrades consider either smaller  t sep with constant N b, or they increase  t sep in proportion to N b

4. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects Electron-cloud build-up in the LHC Beam synchrotron radiation is important provides source of photo-electrons Secondary emission yield (SEY)  (E) is important characterized by peak value  max determines overall e – density e – reflectivity  (0) is important determines survival time of e – Bunch intensity N b and beam fill pattern are important Main concern: power deposition by electrons on the cold beam screen

5. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects Secondary Electron Yield for normal electron incidence R. Cimino et al., Phys. Rev. Lett. 93, 014801 (2004)

6. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects Electron density [m -3 ] during the passage of an LHC bunch in a field-free region HEADTAIL simulation, courtesy E. Benedetto

7. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects Electron density [m -3 ] during the passage of an LHC bunch in an SPS dipole (top view) HEADTAIL simulation, courtesy E. Benedetto

8. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects Electron flux measured in an SPS dipole (strip detector) with LHC beam at 26 GeV courtesy G. Arduini and M. Jimenez

9. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects LHC bunch train at injection in the SPS Evolution of bunch length and bunch population for the first and the last bunch in an LHC bunch train of 72 bunches. SPS measurements with electron cloud in Aug 2004. Courtesy G. Rumolo, G. Arduini, and F. Roncarolo. rms bunch length (ns) bunch intensity (au) time (min) Q x =26.135 Q y =26.185 ξ x =0.15 ξ y =0.1 V RF ~ 3 MV dampers on coupling: 0.008

10. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects   / IP no. of IP’s  Q bb  total SPS0.00530.015 Tevatron (pbar)0.01-0.0220.02-0.04 RHIC0.0024~0.008 LHC (nominal)0.00343~0.01 tune shift from head-on collisions (primary IP’s) tune shift from long-range collisions n par parasitic collisions around each IP conservative value for total tune spread based on SPS collider experience Beam-Beam tune spread for round beams increases for closer bunches or reduced crossing angle limit on   limits N b /(  relative beam-beam separation for full crossing angle  c high-lumi in IP1 and IP5 (ATLAS and CMS), halo collisions in IP2 (ALICE) and low-lumi in IP8 (LHC-b)

11. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects Beam-Beam tune footprints Comparison of tune footprints, corresponding to betatron amplitudes extending from 0 to 6 , for LHC nominal (red-dotted), ultimate (green- dashed), and “large Piwinski parameter” configuration (blue-solid) with alternating H-V crossing only in IP1 and IP5. (Courtesy H. Grote)

12. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects Effects of long-range beam-beam interaction observable at RHIC injection energy (24.3 GeV) with a single proton bunch per ring Bunch intensity N b ~1-2  10 11 Long-Range Beam-Beam Experiment in RHIC, 28 April 2005, Wolfram Fischer et al.

13. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects collision at s=10.65m Long-Range Beam-Beam Experiment in RHIC, 28 April 2005, Wolfram Fischer et al. Beam losses increase when the beam-beam separation at a single parasitic collision point is reduced below ~5 . 1 bunch per ring Blue beam moved vertically Tunes: B (0.739,0.727) Y (0.727,0.738)

14. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects Electron Cloud: recent links & references http://ab-abp-rlc.web.cern.ch/ab-abp-rlc-ecloud/ (web site on Electron Cloud Effects in the LHC) http://icfa-ecloud04.web.cern.ch/icfa-ecloud04/ (ECLOUD’04 workshop, Napa, California, 19 – 23 April 2004) http://www-project.slac.stanford.edu/ilc/testfac/ecloud/elec_cloud.html (web site of ILC Damping Ring Task Force 6) “Can low energy electrons affect high energy physics accelerators?”, R. Cimino, I.R. Collins, M.A. Furmann, M. Pivi, F. Ruggiero, G. Rumolo,Can low energy electrons affect high energy physics accelerators? and F. Zimmermann, Phys. Rev. Lett. 93, 014801 (2004) “Simulation study of electron cloud induced instabilities and emittance growth for the CERN Large Hadron Collider proton beam”, E. Benedetto, D. Schulte, F. Zimmermann, and G. Rumolo, Phys. Rev. ST Accel. Beams 8, 124402 (2005)Simulation study of electron cloud induced instabilities and emittance growth for the CERN Large Hadron Collider proton beam “Update on electron-cloud power deposition for the Large Hadron Collider arc dipoles”, M. Furmann and V.H. Chaplin, LBNL-59062/CBP Note 723/LARP-doc- 157, March 2006, to appear in Phys. Rev. ST Accel. BeamsUpdate on electron-cloud power deposition for the Large Hadron Collider arc dipoles

15. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects Beam-Beam: recent links & references http://wwwslap.cern.ch/collective/zwe/lhcbb/ (web site of LHC Beam-Beam studies) http://www.agsrhichome.bnl.gov/AP/BeamBeam/Workshop03/ (Beam-Beam Workshop, Montauk, Long Island, 19 – 23 May 2003) “Coherent beam-beam modes in the LHC for multiple bunches, different collision schemes and machine symmetries”, W. Herr and T. Pieloni,Coherent beam-beam modes in the LHC for multiple bunches, different collision schemes and machine symmetries Proc. CARE HHH-2004 Workshop, CERN, 8–11 November 2004HHH-2004 Workshop “Progress of Beam-Beam Compensation Schemes”, F. Zimmermann and U. Dorda, Proc. LHC-LUMI-05 Workshop, Arcidosso, 31 Aug–3 Sept 2005Progress of Beam-Beam Compensation SchemesLHC-LUMI-05 Workshop “Beam-beam effects in the Tevatron”, V. Shiltsev, Y. Alexahin, V. Lebedev, P. Lebrun, R.S. Moore, T. Sen, A. Tollestrup, A. Valishev, and X.L. Zhang, Phys. Rev. ST Accel. Beams 8, 101001 (2005)Beam-beam effects in the Tevatron “The effects of solenoids and dipole magnets of LHC experiments”, W. Herr, LHC Project Workshop, Chamonix XV, 23-27 January 2006The effects of solenoids and dipole magnets of LHC experimentsChamonix XV

16. CERN F. Ruggiero Electron Cloud and Beam-Beam Effects CERN Accelerator Complex (not to scale)