1. Electron cloud in the wigglers of ILC Damping Rings L. Wang SLAC ILC Damping Rings R&D Workshop - ILCDR06 September 26-28, 2006 Cornell University

2. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Outline Introduction Simulation Aperture effect Trapping effect Bunch train effect Groove surface Clearing Electrode Comparison with dipole field Summary

3. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Ecloud in DAFNE wiggler? Fast Horizontal instability (larger Horizontal tune shift, 0.01 at 600mA) was found after modification of the wiggler No Vertical instability… KEKB, CESR DAFNE: C. Vaccarezza,etc. ecloud04

4. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 CLOUDLAND 3D PIC code for e-cloud (PRST-AB 124402) Simulation Key parameters (beam,ring,SEY,electrode, …) Mesh Generator Magnetic and electric fields input Space charge solver Charge meshUpdate particle positions Advance particle positions using the new beam and e-cloud space charge fields Preliminary electron generator when beam passing Secondary electron generator Preliminary electron generator Wake field Instability code Future plan --  Parallelize for consistent instability study

5. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Space charge potential solver -FEM Mesh of chamber Three dimensional irregular mesh to better represent the general chamber geometry handle accuracy with high order elements. 20 node element Adaptive mesh for beam/ecloud.

6. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Sample II: Electron cloud with two beams  Two beams  Whole section (12m), without magnets, bunch length 10ns Model : Copper ion N=1  10 9 ; bunchspacing=1 RFbucket, Copper ion N=6  10 9 ; bunchspacing=6 RFbucket, Z RHIC

7. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Optics of New 6km ring

8. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 CESR-c wiggler

9. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Wiggler Field in simulation B0=1.68Tesla Period =0.4m Kx=0

10. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Simulation in wiggler  3D program is required in wiggler (3D field)  Some electrons can effectively move in longitudinal direction (beam direction) and the electron cloud is not uniform in longitudinal direction (different from dipole magnet). the modeling of beam kick, electron motion and space charge field should consider the 3D effects.

11. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Parameters 2767 Bunches: 6 ns bunch spacing with a gap about 43ns, Bunch intensity 2E10, 22 bunches/train 5782 Bunches; 3 ns bunch spacing with a train gap about 38ns; bunch intensity 1E10; 49bunches/train Peak SEY1.75 at 330eV Pipe aperture 44mm

12. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Train gap effect (2767bunches) Bunch Train gaps reduce the electron cloud density by a factor of 10 One train Short train

13. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Effect of pipe aperture, 2767bunches R=22mm R=8mm Ecloud density increases by a factor of 10 when I.D. reduce from 44mm to 16mm

14. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Mirror field trapping No mirror field trapping was found Mirror field

15. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Beam filling pattern effect Low Q beam pattern(5782bunches) has lower electron cloud density (I.D.=22mm)

16. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Comparison with dipole Dipole, B=0.194T Wiggler There is a lower electron density in Wigglers (one order)! (assuming the same initial electrons rate )

17. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Comparison with dipole Wiggler Dipole, B=0.194T The multipacting strips of electron cloud in the wigglers is more close to the beam

18. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Clearing Electrode Strip-line type Wire type Strip-line typeWire type Calculation of the impedance ( Cho, Lanfa) Design & test of impedance is under the way, test in PEPII Dipole & CESR Wiggler Submitted to PRSTAB Suetsugu’s talk

19. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Geometry of Grooved surface (a) Triangular surface (b) Sawtooth surface (c) Overhanging surface

20. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Collection of the stripped electron at injection (SNS)  Foil center(40,23,307)  Magnetic field at foil center=( -3.6, 2504,-547.9) Gauss;  =210mrad  Energy of stripped electrons  =522keV,  =11.98mm, T=0.289ns, v=2.6e8m/s,  =0.866  Catcher shape:  =25 ,  =65  0.34% Carbon 9.2 % Copper L. Wang,et al. PRSTAB 094201(2005)

21. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Triangular grooved surface in wiggler Effective SEY of an isosceles triangular surface with rounded tip.  max=1.74,  max=330eV, B0=0.2Tesla, Rtip=0.2mm, W=4.52mm. Effective SEY from an isosceles triangular surface in a dipole magnetic field.  max=1.74,  max=330eV, B0=1.6Tesla and W=1.89mm To reduce the impedance The effective SEY of triangular grooved surface has very weak dependence on the size W and magnetic field. L wang, T. Raubenheimer, G. Stupakov, (slac-pub-12001) Experiment in PEPII Dipole & CESR Wiggler

22. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Impedance of triangular groove Magnetic field lines penetrating in a groove (a half a period of a groove is shown). The enhancement factor  as a function of angle. Gennady Calculation of impedance with rounded tips is under the way (Gennady, Karl and Lanfa) Machining and extrusion Copper-coated Impedance increases 15%(alfa=70), it will be lower when round tips are used

23. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Summary  Bunch train can effectively reduce the build-up of ecloud in wiggler ( a factor of 10!)  Low Q beam pattern has lower ecloud density  No mirror field trapping was found  Ecloud in wiggler also has two strips, but it is more closer to the beam comparing ecloud in the dipole magnet.  Electron cloud density in wiggler is lower than that in dipole.  Electrodes works in wiggler. (Heat & impedance is the main concerns, Exp. in PEPII and CESR )  Triangular Grooved surface likely works in wiggler, but it would be important to check with realistic field. (Impedance optimization, manufacture) (exp. At SLAC and CESR)

24. ILC Damping Rings R&D Workshop, Cornell, Sep. 27 Acknowledgement Thanks to all colleagues in the damping ring study, especially thanks to K.L.F. Bane, Y. Cai, T. Raubenheimer, G. Stupakov, A.Wolski, J. Gao, S. Guiducci, M. Zisman, M. Palmer, M. Pivi, F. Zimmermann, H. Fukuma, K. Ohmi, E. Kirby, Y. Suetsugu, S. Mark, R. Schlueter, D. Plate, …….