Observations and Predictions for DAFNE and SuperB

1. Observations and Predictions for DAFNE and SuperB Theo Demma - LAL

2. Plan of Talk • Observation and prediction for DAFNE • Introduction • Analysis of the e-cloud induced instabilities @ DAFNE • Coupled bunch • Clearing electrodes for DAFNE dipoles and wigglers • Summary • Predictions for SuperB • Electron Cloud Single Bunch Instability • Simulations • Electron Cloud Build-Up • Dipole • Quadrupole • Summary

3. The DANE Collider BTF

4. E-Cloud effects @ DAFNE • e+currentlimitedby a strong horizontalinstability • Large positive tuneshift with current in e+ ring, notseen in e- ring • Instabilitydepends on bunchcurrent • Instabilitystronglyincreasesalong the train • Anomalousvacuum pressure rise hasbeenoserved in e+ ring • Instability sensitive to orbit in wiggler and bending magnets • Mainchange for the 2003 waswigglerfieldmodification

5. Solenoids installed in free field regions strongly reduce pressure but have poor effect on the instability Most unstable mode -1 Characterization of the Horizontal Instability

6. SolenoidsOff 28/05/20122 VUGPS203 VUGPL201 VUGI2001

7. PEI-M Tracking simulationK.Ohmi, PRE55,7550 (1997),K.Ohmi, PAC97, pp1667. Electron cloud e+bunches z y ~m x • Solve both equations of beam and electrons simultaneously, giving the transverse amplitude of each bunch as a function of time. • Fourier transformation of the amplitudes gives a spectrum of the unstable mode, identified by peaks of the betatron sidebands.

8. Input parameters for DAFNE simulations

9. Mode spectrum and growth rate 60 equispaced bunches Beam current 1.2 A Growth time ~ 100 turn -1 mode (60-5-1=54)

10. Mode spectrum and growth rate -1 mode (120-5-1=154)

11. Clearing Electrodes @ DAFNE To mitigate the e-cloud instability copper electrodes have been inserted in all dipole and wiggler chambersof the machine and have been connected to external dc voltage generators. The dipole electrodes have a length of 1.4 or 1.6 m depending on the considered arc, while the wiggler ones are 1.4 m long.

12. Test of e-cloud clearing electrodesat DAFNE Very positive results: vertical beam dimension, tune shift and growth rates clearly indicate the good behaviour of these devices, which are complementary to solenoidalwindings in field free regions Beam loss above this current if no feedbacks See M. Zobov Talk

13. Summary • Coupled-bunch instability has been simulated using PEI-M for the DAFNE parameters. Results are in qualitative agreement with grow-damp measurements. • Clearing electrodes for DAFNE have been designed, installed, and tested (M. Zobov Talk)

14. Super B mainparameters

15. Single Bunch Instability inSuperB HER Input parameters for CMAD Vertical emittance growth induced by e-cloud • The interaction between the beam and the cloud is evaluated at 40 locations around the SuperBHER tacking into account beam size variations. • The thresholddensityisdetermined by the densityatwhich the growthstarts:

16. Electron cloud buildup simulation • Cloud buildup was calculated by code “ECLOUD” developed at CERN. • Assumptions: - Elliptical or round 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.

17. Build Up Input Parameters for ECLOUD

18. Buildup in Free Field Regions Average electron cloud density =95% Snapshot of the electron (x,y) distribution “just before” the passage of the last bunch Density at center of the beam pipe is larger then the average value.

19. CloudDensityat Center of Beam Pipe Center e-cloud density for = 99% SEY=1.1SEY=1.2SEY=1.3 Center e-cloud density for =95% SEY=1.1SEY=1.2SEY=1.3

20. Electron Cloud Buildup in a 50G Solenoid Snapshot of the electron (x,y) distribution “just before” the passage of the last bunch max=1.4 Solenoids reduce to 0 the e-cloud density at center of beam pipe

21. Buildup in the SuperB arcs: Dipoles HER Arc quadrupole vacuum chamber (CDR) By=0.3 T; =99% SEY=1.0SEY=1.1SEY=1.2SEY=1.3 Snapshot of the electron (x,y) distribution “just before” the passage of the last bunch

22. CloudDensityat Center of Beam Pipe Center e-cloud density for = 99% SEY=1.1SEY=1.2SEY=1.3 Center e-cloud density for =95% SEY=1.1SEY=1.2SEY=1.3 Densities are computed, within a region of 10σx×10σy around the beamcentre.

23. Buildup in the SuperBarcs: Quadrupoles HER 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

24. Single Bunch Instability Threshold Instability occurs if: SuperB V12 where cent. ande,th are obtained from simulations.

25. Summary • Simulations indicate that a peak secondary electronyield of 1.1 and 99% antechamber protection result in a cloud density below the instability threshold. • Planned use of coatings (TiN, ?) and solenoids in SuperB free field regions can help. • Ongoing studies on mitigation techniques (grooves in the chamber walls, clearing electrodes) offers the opportunity to plan activity for SuperB. • Work is in progress to: • Set up a working group to clearly assess the elctron cloud effects in Superb HER and individuate needed countermeasures…. • estimate other effects: multi-bunch instability, incoherent emittance growth...