1. Compton Status ►Introduction ►Recent activities ►Out Look Tohru Takahashi Hiroshima University May 14 2014 AWLC2014

2. Contents Brief review of KEK-Hiroshima cavity Recent progress Future Prospects

3. 29 th Mar 2013 detector γ Laser cavity ATF parameter 1.3GeV 1×10 10 electron/bunch Up to 10 bunch/train 2.16×10 6 turn/s Setup at the KEK-ATF

4. The KEK-Hiroshima Cavity IP Plane Mirror Concave Mirror Plane Mirror Concave Mirror Main Parameters Circumference:1.68m Finesse:4040(Measured) Power Enhansement:1230

5. Stored Power [w] Right pol Left pol Sotred power Laser Power: 2.6kW w/ 38W fractuation 14 th Sep 2012 Stored Laser Power in the cavity must control ΔL<<110pm achieved ΔL<<16pm

6. ATF 2.16MHz ~2.6×10 8 /sec 5bunches/train 2970±20 MeV ⇒ ~120  s / train のガンマ線に相当  ray Generation e- laser  5.6ns E  [MeV]

7. Issues Power drops after ~6s suspected thermal effect on the mirrors Transmission ６s６s Beam profile is elliptic elliptic at the focalpoint too Uesugi Injection Transmission PM Monitor Focal Point

8. Systematic investigation of the profiles at the focal point Profiles at the focal point can be observed outside Pellicle mirror ： (2 μm thick half mirror) ( R < 10% ) Image of the focal point Laser inLaser out Focal point in the cavity Uesugi

9. Profiles at 3 focal spot sizes 15 μm 23 μm 20 μm 26 μm 25 μm 30 μm 長軸 / 短軸長さ（ σ ） [μm] axis of propagation Z [mm] (Z = 0: min. of minor axis ） ●major ■minor ●major ■minor ●major ■minor Laser profiles near the focal point Profile at Z=0 (~ focal point) Uesugi ）

10. 長軸 / 短軸長さ（ σ ） [μm] 伝播方向 Z [mm] （短軸 σ が最小の位置を基準 Z = 0 ） ━ major ━ mainor 20 μm 25 μm 15 μm Caculation with trans. matrix Laser profiles at the focal point ●major ■minor ●major ■minor ●major ■minor ━ major ━ minor 上杉（広島大）

11. 長軸 / 短軸長さ（ σ ） [μm] 伝播方向 Z [mm] （短軸 σ が最小の位置を基準 Z = 0 ） ━ major ━ minor 20 μm 25 μm 15 μm Caculation with trans. matrix Laser profiles at the focal point ●major ■minor ●major ■minor ●major ■minor ━ major ━ minor 上杉（広島大） Round shape, reasonable agreement with calculation at larger laser spot size

12. Issues for high power cavity

13. Toward high power storage Treatment of high reflectivity mirrors – Clean environment at KEK-ATF area Clean booth modification of vacuum chamer More precise feedback control – High finesse test bed at Hiroshima *Beam profile does not matter unless we want to focus down to near design minimum

14. Hoist-less manipulation of the cavity hinges

15. Hoist-less manipulation of the cavity hinges

16. Laser room at Hiroshima 4Mirror cavity is set – laser resonance has been verified – preparation for high finesse in progress

17. Plan in JFY2014 A few times more power at KEK-ATF cavity – O(10) higher reflectivity －＞ Max. 5 times more due to the CEO – Assuming no power dissipation on mirror －＞ 2times more – －＞ 2.8kW->28kW （ more with injection efficiency ） At Hiroshima – The same mirror with used in KEK －＞ 13,000 power enhansement – w/ CW laser at Hiroshima (0.2W) －＞ 1.3kW – more power w/ laser an amplifier? – development of digital feedback proof of principle -> realization