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Optical Cavity R&D around KEK-ATF

Optical Cavity R&D around KEK-ATF. T.Takahashi Hiroshima Univ. Nov. 2008 LCWS08 at Chicago. an idea. Klemiz , Monig. Experimental R/D in ATF. Hiroshima- Waseda -Kyoto-IHEP-KEK. Make a fist prototype 2-mirror cavity. L cav = 420 mm. Put it in ATF ring. accuracy ~ 0.8 m m.

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Optical Cavity R&D around KEK-ATF

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  1. Optical Cavity R&D around KEK-ATF T.Takahashi Hiroshima Univ. Nov. 2008 LCWS08 at Chicago T.Takahashi Hiroshima

  2. an idea Klemiz, Monig

  3. Experimental R/D in ATF Hiroshima-Waseda-Kyoto-IHEP-KEK Make a fist prototype 2-mirror cavity Lcav= 420 mm . Put it in ATF ring

  4. accuracy ~ 0.8mm Set up at KEK-ATF Optical cavity electron beam Cavity position is moved Vertical Horizontal

  5. Feedback to Achieve 3 Conditions pulse stacking cavity Lcav = n  Lcav = m Llaser mode locked laser Laser freq = Ring RF

  6. Transmitted light The appearance of light resonance signal Mirror reflectivity : 99.6% Mode locked laser PD Transmitted light (Photo diode) 0.7nm ~l/enhacement/p the optical cavity is on resonant Reflected light time (ms) 1ms Continued to change the length of the external cavity.

  7. Cross-feedback=Closed loop (Sakaue) PID Piezo offset Laser PD laser light pulses sync. to Acc. keep resonance Phase Detector RingRF Piezo Stacking Cavity Ref-light

  8. 2-mirror-cav to 4-mirror-cav. 2-mirror cavity 4-mirror cavity e-beam laser beam Spot size = 30 um Enhance = 1000 R. Cizeron Spot size = 10 um Enhance = 10000 difficult to achieve both high enhancement and small spot

  9. 2D configuration α Focal points for horizontal and vertical are not same 3D configuration

  10. R&D of 4 mirrors cavity started

  11. Tworesonat peaks due to geometrical phase Right Linear Left

  12. Summary and prospects • photon generation by Laser pulse stacking cavity / accelerator has been demonstrated both for • Polarized electron source (PosiPol) • hard x ray generation (LUCX) • A project for x ray source has started • All projects going to 4 mirror ring cavity • Technique with Ring cavity and e-beam will be accumulated in next 3-4year • Specific study is for 100 m long cavity is necessary • supporting 1m scale mirrors • adaptive optics to maintain phase front • Feed back experiment to cavity design • 3 Dimensional cavity • polarization T.Takahashi Hiroshima

  13. Optical Cavity R&D around ATF • O(10MeV) gs for Compton Based Polarized Positron source. • Hard X ray (~30keV) sources • LUCX project • New 5 year project • Compact X ray source w/ SRF electron accelerator and pulse stacking cavity. Accumulating technique and experiences w/ cavity and accelerators. ring cavities are being planned as next step T.Takahashi Hiroshima

  14. data summary Stacked Laser power[W] bunch /train current [mA] normarized gs/A/W gs/crossing exectation Normalized g yield seems to decrease as # bunches/train goes up Bunch (size, timing) fluctuation in the ATF suspected

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