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

collaborators Feedback R&D for Optical Cavity 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 19 th Feb 2013 Special thanks for French Team

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

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

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

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

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

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

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

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

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

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

Gamma-ray yield 5bunch/train(7.7mA) Gamma energy [GeV] Count ~2.6×10 8 /sec 2970±20 MeV ⇒ ~120  s/train Feedback R&D for Optical Cavity 19 th Feb 2013

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

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

summary ◇ R&D e+ source using laser Compton ◇ gamma-ray yield = 2.6×10 8 /sec ◇ cavity have stack power limit by thermal effect Feedback R&D for Optical Cavity 19 th Feb 2013