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R&D Status of Optical Cavity for ILC Polarized e+

R&D Status of Optical Cavity for ILC Polarized e+. Hiroki Sato Hiroshima University. Polarized e+ generation in optical cavities. Refer to Urakawa and Omori’s talk. Optical Cavity. R & D Issues of optical cavities. To achieve high  yield

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R&D Status of Optical Cavity for ILC Polarized e+

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  1. R&D Status of Optical Cavity for ILC Polarized e+ Hiroki Sato Hiroshima University

  2. Polarized e+ generation in optical cavities • Refer to Urakawa and Omori’s talk Optical Cavity

  3. R & D Issues of optical cavities • To achieve high  yield • Use mode-locked (pulse) laser synchronized with electron repetition rate (bunch spacing) • High multiplication factor (power gain) <- high reflectivity mirrors and feedback system • Smaller waist size • Smaller crossing angle

  4. Pulse stacking cavity Scattered Gamma beam 42cm Cavity Laser Repetition rate : 357MHz laser pulses Phase Scan Electron repetition rate : 357MHz Electron bunches Compton Scattering in every 357MHz Resonance condition Lcav=n (n: integer) Lcav=mLlaser (m: integer)

  5. Basic parameters

  6. Expected number of events and energy spectrum Bunch length ＝9mm (rms) Calculated by T. Takahashi

  7. KEK-ATF Damping Ring   ray detector Compton Cavity Start experiment in October 2006

  8. Compton Cavity Ext. Cavity: Cavity: Super Invar Cavity length: 420 mm Mirrors: Reflectivity: 99.9% (gain =1000) Curvature: 210.5 mm (w0 = 59μm)

  9. Test bench status (small waist size) • Successfully accumulate CW laser in 420mm cavity with mirror curvature of 210.5mm and 99.7% reflectivity.

  10. Chamber design • Sakaue’s design for the LUCX experiment (next talk) will be our baseline. • We aim to achieve crossing angle of 10 degrees. 20 degrees 10degrees e-

  11. Milestones • May 2006~ • Make a moving table for the Compton cavity and optical setup -> control the collision point within 1m accuracy • Design and build a vacuum chamber and Compton cavity • Achieve 59m waist size (29m in rms) with 99.9% reflectivity mirrors and feedback system in the test bench • August 2006~ • Install the chamber • October 2006~ • Install 10W laser • Start experiment

  12. Optical cavity using parabolic mirrors • Can independently adjust waist size and cavity length • Matching is relatively easier • Scav~R2(1+R32R4)/(1-R22R32R4) -> Reflectivity of parabolic mirrors should be large (close to 1) • High-reflectivity (~99.5%) parabolic mirrors are expensive (~$30k/mirror) and smaller off-axis angle (<=20 degrees) Tcav Flat mirror R1,T1 R4,T4 ｆ R2,T2 Parabolic mirror R3,T3 Scav

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