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Update on Electron Cloud Simulations

Update on Electron Cloud Simulations. T. Demma, INFN-LNF. Plan of Talk. Electron Cloud Single Bunch Instability Simulations Electron Cloud Build-Up Dipole Quadrupole Mitigation Techniques Summary. Single-bunch instability mechanisms*.

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Update on Electron Cloud Simulations

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  1. Update on Electron Cloud Simulations T. Demma, INFN-LNF

  2. Plan of Talk • Electron Cloud Single Bunch Instability • Simulations • Electron Cloud Build-Up • Dipole • Quadrupole • Mitigation Techniques • Summary

  3. Single-bunch instability mechanisms* *See F. Zimmermann: Review of Single Bunch Instabilities driven by El. cloud

  4. Preliminary results for SuperB =5x1011 =4x1011 =3x1011 Vertical emittance growth induced by e-cloud Input parameters (LNF conf.) for CMAD • The interaction between the beam and the cloud is evaluated at 40 Interaction Points around the SuperB HER (LNF option) for different values of the electoron cloud density. • The threshold density is determined by the density at which the growth starts:

  5. Buildup in Free Field Regions Snapshot of the electron (x,y) distribution 50G solenoids on Snapshot of the electron (x,y) distribution Solenoids reduce to 0 the e-cloud density at center of beam pipe Density at center of the beam pipe is larger then the average value.

  6. Emittance growth in SuperB HER (V12) Beam Cloud interaction evaluated at magnetic regions (dipoles) only el= 9x1011 [e-/m3] el= 10x1011 [e-/m3] el= 11x1011 [e-/m3]

  7. Electron cloud buildup simulation • Cloud buildup was calculated by code “ECLOUD” developed at CERN. • Assumptions: - Elliptical Chambers - Uniform production of primary electrons on chamber wall. - A reduced number of primary electrons is artificially used in order to take into account the reduction of electron yield by the ante-chamber: e-/e+/m=dn/ds Y (1-) where: dn/ds is the average number of emitted photons per meter per e+, Y is the quantum efficiency, and  is the percentage of photons absorbed by the antechambers.

  8. Input Parameters

  9. Buildup in SuperB V12 HER Dipoles By=0.3 T; =95%SEY=1.1

  10. Buildup in the SuperB arcs: Quadrupoles LER Arc quadrupole vacuum chamber (CDR) dBy/dx=2.5T/m, =99% max=1.2 average center Snapshot of the electron (x,y) distribution “just before” the passage of the last bunch OLD PARAMETERS

  11. Single Bunch Instability Threshold th= 1012 [e-/m3]

  12. Summary • Single bunch instability simulations for SuperB HER V12 taking into account the effect of solenoids have been performed using CMAD. They indicate a threshold density of ~1012 e-/m3 (roughly 2 times previous estimates). • Build-up simulations Indicate SEY<1.2, eta < 0.05 as safe region for the single-bunch instability.. • But: • which is the confidence to reach this region in the parameter space even including countermeasure such as antechambers, coatings, grooves, clearing electrodes..? • Do we have reliable estimates (measurments) for parameters such as PEY, photon reflectivity…? • See following Talks

  13. Buildup in ilc-DR arcs: Dipoles By=0.27 T; R=50% =90%=97% By=0.27 T; R=20% =90%=97% Average e-cloud density Average e-cloud density

  14. Mitigation Techniques: SEY reduction Is it possible to do the same for SuperB?

  15. e-cloud @ DAFNET. Demma, ‘’Electron cloudsimulationsfor DAFNE’’, ICFA BeamDyn. Newslett. 48, 2009. Mode Specrtrum computed by PEI-M -1 mode (120-5-1=154) Input Parmeters Growth Rate Comparison Multiparticle tracking using PEI-M (K. Ohmi, KEK) Uniform Magnetic Field By=1.7 T

  16. e-Cloud @ DAFNE: Clearing ElectrodesD. Alesini, T. Demma et al. , in Proc. of IPAC 2010. Electric Field as computed by POISSON • Clearing electrodes are installed in the vacuum chambers of wigglers and dipoles of DAFNE positron ring. • Simulation using ECLOUD (CERN) • See A. Drago Talk Electron cloud density evolution 0 50 100 150 200 250 300 350 Time (ns)

  17. Summary • Single bunch instability simulations for SuperB HER V12 taking into account the effect of solenoids have been performed using CMAD. They indicate a threshold density of ~1012 e-/m3 (roughly 2 times previous estimates). • Build-up simulations Indicate SEY<1.2, eta < 0.05 as safe region for the single-bunch instability.. • But: • which is the confidence to reach this region in the parameter space even including countermeasure such as antechambers, coatings, grooves, clearing electrodes..? • Do we have reliable estimates (measurments) for parameters such as PEY, photon reflectivity…? • Set up a working group to try answer these questions also profiting on the experiences made in the framework of other collaborations or laboratories (ILC-DR, CesrTA…)

  18. Spares

  19. Long Term Emittance growth • Radiation Damping is not taken into account!

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