1. T.Takahashi Hiroshima 1 2007/11/5 Tohru Takahashi Hiroshima University 高橋 徹 広島大学

2. T.Takahashi Hiroshima 2 Why polarized positrons electrons are polarized,,,,,,  choose helicity of its counter part if unpolarized e+ a half of the beam is thrown away

3. T.Takahashi Hiroshima 3 electon beam is polarized but,,,, In principle, we can suppress this by polarized electrons if we want but

4. polarization (either e- or e+) has to be well controlled Positron polarization Positron polarization helps much to : increase luminosity effectively suppress background physics is sensitive to the polarization

5. ILC: e+ Polarization from Beginning? To use the e+ polarization for physics we strongly ask to provide a machine with flexible helicity reversal also for the positron beam No or very rare reversal of e+ helicity could be worse than no e+ polarization Positron Pol WG Reminder: Positron Pol is important for numerous physics channels Gain in production rate Reduction of Bckgrnd Access to new channels J.Hewett LCWS07 SUSY, New Phys. summary

6. How to get them Helical Undulator Ee~150GeV L>150m Ee~GeV Laser Compton

7. T.Takahashi Hiroshima 7 pros and cons Compton based positron polarization independent of main linac good capability of controlling polarization R& D issues how to get enough intensity

8. T.Takahashi Hiroshima 8 Proof of Principle at KEK - ATF

9. T.Takahashi Hiroshima 9 To meet ILC requirements Requirements for ILC 2x10 10 /bunch ~3000 bunches/train 5Hz ideas to meet requirement Single pass Linac based Recycling e- and Lasers e- Storage ring + optical cavity Energy Recovery Linac(ERL) + optical cavity

10. Linac Scheme T.Takahashi Hiroshima 10 4GeV, 1A 15MeV e+  Co 2 laser 1J  Single pass 5x10 11   2x10 10 e+ V.Yakimenko ~2m directly creates enough e+ high current e- source, regenerative laser cavity ?

11. capture system Compton Ring Scheme T.Takahashi Hiroshima 11 1.3 GeV e- source Electron Storage Ring Optical Cavities target damping ring main linac 6.15ns  electron bunches stored in the ring  laser pluses are stacked in the optical cavities -> 600mJ  stacking 100 bunches on a same bucket in the DR -> 2.4x10 10 e/bunch 2.4x10 8 e+ 1.7x10 10  high repetion e- source optical cavity, pulse staking, e- quality in ring ?

12. capture system ERL Scheme T.Takahashi Hiroshima 12 e- gun Energy Recovery Linac Optical Cavities target damping ring main linac 6.15ns  get fresh e bunches by ERL  laser pluses are stacked in the optical cavities -> 600mJ  continues stacking ~1000 bunches on a same bucket in the DR -> 2x10 10 e/bunch 2x10 7 e+ 6.4x10 9  dump high repetition e-, fresh e- each turn, higher pol. optical cavity, ERL, bunch stacking ?

13. CR/ERL simulations studies (Kharkov, LAL, JAEA, KEK) design studies Optical Cavity (LAL,IHEP, Hiroshima, KEK) e+ capture (LAL, ANL) We will start collaboration with KEKB upgrade study e+ stacking in DR (CERN) Basic beam dynamics studies Laser Fiber laser / Mode-lock laser (cooperation with companies) CO2 laser (BNL) experimental R/D beam dynamics studies omori R&D times

14. 325 MHz Cavity Enhancement Factor = 1000 - 10 5 Laser-electron small crossing angle Laser bunches L cav = n L cav = m L laser Omori Laser pulse stacking cavity

15. 4-mirror cavity (LAL) 2-mirror cavity (Hiroshima/KEK) high enhancement very small spot size complicated control moderate enhancement small spot size simple control Prototypes accumulate experiences w/ beam at ATF to ATF later

16. Experimental R/D at ATF ATF at KEK 2 mirror FP L cav = 420 mm for 2.8ns bunch spacing

17. installed into the ATF DR last September

18. World-Wide-We b of Laser Compton

19. T.Takahashi Hiroshima Pulse Stacking Cavity for  colliders K. Moeing 100 m long pulse stacking cavity surrounding the detector opticalcavity for  collisers = (pluse + small spot size + high power) + (larger scale) ~ polarized positron + gravitational wave

20. Summary  Polartized Positron is useful and preferable to be implemented at the early stage of the ILC  Laser-Compton scheme looks attractive  Many common efforts can be shared in various applications.  State-of-the-art technologies  Laser, Optical cavities,ERL Stay tuned and Join us

21. 25/05/2007 POSIPOL 2007 21 e- beam tube beam Interaction point e- beam 4 mirror cavity at LAL intend to be installed into ATF

22. T.Takahashi Hiroshima 22 Proof of Princple at KEK - ATF

23. Pros and Cons T.Takahashi Hiroshima 23  Linac Scheme  High  gen by one pass; no stacking in DR  10nc 5ps e- source  high power Co 2 laser: regenerative cavity  Ring Compton  moderate laser power w/ optical cavity  100 stacking  optical cavity R&D  beam life, stability on the Compton Ring  Crab crossing?  ERL  moderate laser power w/ optical cavity  high  yield /w stacking  higher polarization  200 ~ 1000 staking  optical cavity R&D  Energy recovery after compton Optical cavity bunch stacking seems

24. CO 2 Laser system for ILC intra-cavity pulse circulation : – pulse length 5 ps – energy per pulse1 J – period inside pulse train12 ns – total train duration1.2  s – pulses/train 100 – train repetition rate150 Hz – Cumulative rep. rate15 kHz – Cumulative average power15 kW Kerr generator IP#1IP#5 2x30mJ CO 2 oscillator 10mJ 5ps from YAG laser 200ps 1  J 5ps 10mJ 5ps 300mJ 5 ps TFPPC 150ns Ge 1J e-e-

25. T.Takahashi Hiroshima 25 Positron Sources Polarized Electron source Positron Source electronpositron

26. T.Takahashi Hiroshima 26 Pros and Cons ComptonHelical Undulator Indepedence need 150GeV e- from main linace independent of main linac Tunability need deceleration for low energy operation Pol. flip not foreseen yetno problem e+ intensity OK? intense  bunch stacking

27. T.Takahashi Hiroshima 27 Principle of Pol. e+ generation by Compton Scattering Omori laser