Compton Status

►Introduction►Recent activities►Out Look

Tohru TakahashiHiroshima University

May 14 2014 AWLC2014

Contents

• Brief review of KEK-Hiroshima cavity

• Recent progress

• Future Prospects

29th Mar 2013

detectorγ

Laser cavity

ATF parameter1.3GeV1×1010 electron/bunchUp to 10 bunch/train2.16×106 turn/s

Setup at the KEK-ATF

The KEK-Hiroshima Cavity

IP

Plane Mirror

Concave Mirror

Plane Mirror

Concave Mirror

Main ParametersCircumference:1.68mFinesse:4040(Measured)Power Enhansement:1230

Stored Power [w]

Right polLeft pol

So

tre

d p

ow

er

Laser Power: 2.6kWw/ 38W fractuation

14th Sep 2012

Stored Laser Power in the cavity

must controlΔL<<110pm

achievedΔL<<16pm

ATF 2.16MHz ~2.6×108/sec

5bunches/train

2970±20 MeV ⇒ 　 ~120γs / train のガンマ線に相当

γray Generation

e-

laser

γ

5.6ns

Eγ[MeV]

Issues

Power drops after ~6s suspected thermal effect on the mirrors

Transmission６ s

Beam profile is elliptic elliptic at the focalpoint too

Uesugi

Injection TransmissionPM

Monitor

Focal Point

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 thefocal point

Laser in Laser out

Focal point in the cavity

Uesugi

Profiles at 3 focal spot sizes

15 μm

23 μ

m

20 μm

26 μ

m

25 μm

30 μ

m

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 ）

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 μm15 μm

Caculation with trans. matrix

Laser profiles at the focal point

●major■minor

●major■minor

●major■minor

━major━minor

上杉（広島大）

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 μm15 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

Issues for high power cavity

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

Hoist-less manipulation of the cavity

hinges

Hoist-less manipulation of the cavity

hinges

Laser room at Hiroshima

• 4Mirror cavity is set– laser resonance has been verified– preparation for high finesse in progress

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