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Feedback R&D for Optical Cavity

Feedback R&D for Optical Cavity. Ryuta TANAKA (Hiroshima univ.). 19 th Feb 2013 SAPPHiRE DAY. 19 th Feb 2013. Feedback R&D for Optical Cavity. collaborators. Hiroshima university R. Tanaka, T. Akagi, T. Takahashi, H. Yoshitama. KEK S. Araki, Y. Funahashi, Y. Honda, T. Okugi,

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Feedback R&D for Optical Cavity

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  1. Feedback R&D for Optical Cavity Ryuta TANAKA (Hiroshima univ.) 19th Feb 2013 SAPPHiRE DAY

  2. 19th Feb 2013 Feedback R&D for Optical Cavity collaborators Hiroshima university R. Tanaka, T. Akagi, T. Takahashi, H. Yoshitama KEK S. Araki, Y. Funahashi, Y. Honda, T. Okugi, T. Omori, H. Shimizu, N. Terunuma, J. Urakawa Waseda university K. Sakaue, M. Washio Special thanks for French Team

  3. 19th Feb 2013 Feedback R&D for Optical Cavity contents • Positron source using laser Compton • Cavity control • Gamma yield • issue

  4. 19th Feb 2013 Feedback R&D for Optical Cavity Introduction Polarized e+ by laser Compton Scheme laser e- Gamma ray proof of principle experiments M. Fukuda et al., Physical Review Letters 91, 164801(2003) T. Omori et al., Physical Review Letters 96, 114801(2006) Toward the positron sources -> increase intensity of gamma rays

  5. 19th Feb 2013 Feedback R&D for Optical Cavity Increase laser intensityusing laser cavity For increase gamma-ray yield =Increse Laser intensity at interaction point with electron Gamma-ray Laser pulse laser cavity Electron beam • High efficiency collision by timing synchronization • electron and laser pulse • Increase of laser intensity by resonance of laser cavity • Condensed laser at IP

  6. 19th Feb 2013 Feedback R&D for Optical Cavity Experiments at the KEK ATF Laser cavity γ detector ATF parameter 1.3GeV 1×1010 electron/bunch Up to 10 bunch/train 2.16×106 turn/s

  7. 19th Feb 2013 Feedback R&D for Optical Cavity laser cavity Plane mirror Plane mirror Concave mirror IP Concave mirror

  8. 19th Feb 2013 Feedback R&D for Optical Cavity Polarization property • geometric phase due to twisted pass • cavity only resonates with circular polarization • Different resonance point in left and right polarization L-pol R-pol Cavity length

  9. 19th Feb 2013 Feedback R&D for Optical Cavity Control method using Polarization property Different slope in left and right pol.

  10. 19th Feb 2013 Feedback R&D for Optical Cavity Advantage in the control method exchange polarity feedback loop is exchange stack laser pol. ->e+ pol. can be controlled by the polarity control loop R-pol power L-pol power PD QWP PD Transmitted power PBS PD

  11. 19th Feb 2013 Feedback R&D for Optical Cavity Cavity control L-pol Stack power R-pol 110pm control 1.4% fluctuation ->4pm Laser power = 2.6kW Timing jitter = 8ps stack power [W]

  12. 19th Feb 2013 Feedback R&D for Optical Cavity Laser size at IP laser Electron beam (σe=10um) Gamma yield [A.U] σ= 17um ->σl=13um Vertical position [um]

  13. 19th Feb 2013 Feedback R&D for Optical Cavity Gamma-ray yield 5bunch/train(7.7mA) 2970±20 MeV ⇒~120gs/train Count ~2.6×108/sec Gamma energy [GeV]

  14. 19th Feb 2013 Feedback R&D for Optical Cavity Gamma-ray yield each bunch laser 5bunches/train g e- 5.6ns Gamma yield [A.U.] Bunch current [A.U.] time [ns] time [ns] no bunch dependence ( yield is proportional to e- current)

  15. 19th Feb 2013 Feedback R&D for Optical Cavity Thermal effect Target: more intensity stacking Feedback on Transmitted power When low power Reflected power 20s Thermal deformation of the mirror ->Change of transmitted profile =Incident efficiency is reduced ->make stacking power limit

  16. 19th Feb 2013 Feedback R&D for Optical Cavity summary ◇R&D e+ source using laser Compton ◇gamma-ray yield = 2.6×108/sec ◇cavity have stack power limit by thermal effect

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