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