Collaboration on Beam Instability Study

1. Collaboration on Beam Instability Study Presented by Z.Y. Guo Institute of High Energy Physics Beijing 100039, P.R. China 2004-6-17

2. 1. General Description • Very tight collaborations between KEK and IHEP • on the beam instability studies. • Under the support of Core University Program, • the collaborations are strengthened. • This collaboration mainly covers the following aspects in the • subject of beam instability experimental and simulation: • Electron cloud instability (ECI) • Bunch lengthening • Coupling impedance and other related items

3. Collaborations on ECI Study in BEPC

4. What is ECI Electron Cloud Instability Electron cloud density Model Secondary e- e- g e+ beam Beam chamber

5. Electron cloud density 60 bunches pass in every 8ns (BEPCII)

6. Coupled-bunch instability caused bythe electron cloud • Wake field is induced by the electron cloud. • Coupled bunch instability due to the wake field causes beam loss. • Beam blow-up degrades the luminosity.

7. History of ECI • Coupled-bunch instability observed at KEK-PF. • Interpretation of the instability using photo-electron cloud model. • The instability was observed at Beijing Electron Positron Collider (BEPC) • Study of electron cloud effect for the design of KEKB and BEPCII.

8. Importance of ECI • Happens in the high intensity factory-like • machines • Strongly limits the luminosity of colliding beams • Causes coupled bunch oscillation • Should be considered at the beginning of • the newly designed positive charged machine. • It is very important to understand the mechanism • of ECI and try to cure it as much as possible.

9. ECI study in BEPC • Started from 1996 • Collaborated with KEK, more than 10 times • experiments on ECI in BEPC together with • KEK people • Partly supported by JSPS from 2000 • Analyses and simulation study on EC/ECI • Achieve fruitful results now

10. Experimental Study On Electron Cloud Instability

11. Some results on ECI studied in BEPC Vertical betatron sidebands observed in BEPC

12. Vertical betatron sidebands of 160-bunch beam observed in BEPC

13. Mode spectra by single path beam position monitor

14. EC detectors installed on BEPC

15. EC as a function of the bias voltage on detector

16. Energy dependence on chromaticity at ECI threshold

17. Solenoid wound on the straight sections in BEPC

18. Vertical bunch size solenoid off (upper) and solenoid on (lower)

19. EC current with different solenoid strength

20. Betatron sidebands amplitude with different chromaticity and solenoid strength

21. Experiment on electrode effect

22. BPM button applied DC voltageas clearing electrodes on EC

23. Experiment on electrode effect Beam size vs. voltage on buttons off (up) and on (down) head of bunches (left) and tail of bunches (right)

24. Octupole effect experiment Amplitude of sideband (left) and bunch size (right) vs. octupole strength

25. Simulation Study on Electron Cloud Instability

26. Simulation study for BEPCII Simulations on EC production in elliptical (upper), antechamber (mid) and antechamber with clearing electrodes (lower) (Code by Dr. Y. Liu, IHEP)

27. Simulations on EC density with different width of antechamber of BEPCII

28. Growth of the coupled bunch oscillation

29. Ecloud position Bunch slices Simulation approaches for single bunch • Concentrate e− cloud at one location of the ring • Represent bunch and e- with macro-particles

30. Increase of bunch size at different electron cloud density

31. Single bunch oscillation

32. Single bunch instability Start 500 turns 1000 turns Head tail oscillation in a bunch EC density is 1.0x1012 above the threshold

33. Simulation on bunch sizes at different chromaticity

34. Suggested methods to cure ECI from studies • Antechamber • TiN coating of the inner surface, and photon absorber • Larger chromaticity, and octupole • Transverse feedback system • Solenoid winding • Clearing electrode and BPM

35. 3. Papers and students • There are many papers published on the beam instability studies which indicate the meaningful study results in these years. • A few students partly join the collaboration studies

36. Papers published in 2000/2001 • Z.Y. Guo et al, Beam Instability Studies in the BEPC, EPAC2000 Proceedings, p1127 • Z.Y. Guo et al, Experiment to measure the Electron Cloud at BEPC, PAC01, FOAB003 • K.C. Harkay, Z.Y. Guo et al, Survey of Recent Results on Electron Cloud Effects in Photon Machine, PAC01, FOAB002 • Z.Y. Guo et al, Studies on the Photoelectron Cloud at the BEPC, APAC01, WEBU03 • J.Q. Wang , Preliminary Study of the BEPCII Impedance, APAC01, WEBU04 • Q. Qin, Collective Effects in the BEPCII Single-Ring Scheme, APAC01, WEBU05 • Q. Qin et al, Study on Electron Cloud at the BEPC, The International Workshop on Two-Stream Instabilities • Z.Y. Guo et al, The study on Beam Photoelectron Instability in BEPC, Published on High Energy Physics and Nuclear Physics (in Chinese) • T. Naito, Q. Qin et al, Bunch Length Measurement in the ATF Damping Ring, KEK-ATF-01-01, IHEP-AC-AP-Note/2001-15 • Q.Qin et al. Studies on bunch lengthening at the BEPC, NIM A, Vol 463, 77, 2001

37. Papers published in 2002 • J. Xing et al, Simulation Study on ECI for BEPC and ZBEPCII, ECLOUD02 Proceedings, p235 • Z. Zhao et al, Bunch Length Measurement on BEPC, Published on High Energy Physics and Nuclear Physics (in Chinese) • Z.Y. Guo et al, Two Stream Instability in Storage Ring, The Eighth Particle Accelerator Physics Symposium (in Chinese) • J.Q. wang et al, Collective Effects Study for BEPCII, EPAC02 Proceedings p1583 • Z.Y. Guo et al, Experimental Studies of the Photoelectron Instability in the Beijing Electron Positron Collider, PRST-AB, Vol. 5, 124403 • Z.Y. Guo et al, Measurement Study on Electron Cloud in BEPC, BEPC Annual Meeting (in Chinese)

38. Papers published in 2003 • Y.D. Liu et al, Simulation of the Electron Cloud Density in BEPCII, Published on High Energy Physics and Nuclear Physics (in Chinese) • Z.Y. Guo et al, Electron Cloud Measurement in BEPC, IHEP-AC-AP-Note/2003-15 (in Chinese) • Y.D. Liu et al, Experiment of Clean Electrode on ECI in BEPC, IHEP-AC-AP-Note/2003-30 (in Chinese) • Y.D. Liu et al, Experiment of Solenoid on ECI in BEPC, IHEP-AC-AP-Note/2003-35 (in Chinese)

39. Papers published in 2004 • Q. Qin, Collaborations between IHEP & KEK: Results and Future, ATF meeting, March 2004 • Y.D. Liu et al, Simulation of the Electron Cloud Instability for BEPCII, APAC04 Proceedings • Q. Qin et al, Recent Experimental study on ECI at the BEPC, APAC04 Proceedings • Z.Y. Guo et al, The studies of Electron Cloud Instability, APAC04 Proceedings • Z.Y. Guo et al, Experiment of Electron Cloud Instability in BEPC, IHEP-AC-AP-Note/2004-03 More than 26 papers published since 2000

40. students partly join the collaboration • Dr. Luo Yun, IHEP, Two stream instability, 2000 • Dr. Huang Gang, THU, Beam feedback, 2002 • Dr. Ge Jun, THU/IHEP Longitudinal Microwave Instability, 2003 • Dr. Liu Yudong, IHEP, ECI simulation and experiment, 2001-2004 • Dr. Wang Lin, USTC, Stability related RF system, 2003

41. 4. Conclusions • Collaborations between KEK and IHEP are progressed smoothly in the aspect of beam instability studies. • Fruitful results on the collaborations are achieved, which is very important to not only the beam performance, but the accelerator research. • Future collaborations are important and will bring further achievements.

42. Thanks for attention