status of the optical cavity r&d at atf iwlc2010 geneva 20-october-2010 t.takahashi hiroshima...
TRANSCRIPT
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Status of the optical cavity R&D
at ATF
IWLC2010Geneva 20-October-2010
T.TakahashiHiroshima Universityfor collaborators
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an ideaKlemiz, Monig
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an ideaKlemiz, Monig
no dedicated R&D program for photon colliders but projects for laser-Compton scattering with optical cavity
Polarized positron sources x-ray sources
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Prototype Cavities
4-mirror cavity at LAL
2-mirror cavity at KEK ATF
high enhancement, small spot size
experiences with accelerator
4-mirror test bed at KEK
moderate enhancementmoderate spot sizesimple control
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STATUS OF THE 2 MIRROR CAVITY
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Experimental R/D in ATF
prototype 2-mirror cavity
Put it in ATF ring
Hiroshima-Waseda-Kyoto-IHEP-KEK
Lcav = 420 mm
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AFTER TILC09
►One of the Mirror was replaced with the higher reflectivity one
– 99.6% -> 99.9%
– power enhancement ●250 -> ~750
– more precise controll required (~0.1nm)
►Status of the cavity w/ new mirror
– Finess ~2000 with feedback on before vacuum on
– now in preparation for beam
– hope to get 3 times more photons by the end of the year
99.9%99.6%
slide at ALCPG09
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W/ Larger enhancement cavity in 2009
10.8g/train at 1 bunch (2.2ma)26.8g/train10cunches(6.7mA)
demonstration of 3 times more g by beam tuningbunch by bunch observation soon
After, extensive studies; Power enhancement of the cavity ~ factor 3 Laser power 500W to 1.48kW
The electron beam was not tuned enough in 2009
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Miyoshi PosiPol2010
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4 MIRROR CAVITY
to get higher enhancement and smaller beam waist
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We should go to 3D 4 mirror ring cavity
to get small sport size
2 mirros is not stable for small spot size
α
2d 4M has astigmatism
3D (or twisted)4M ring cavity
to position in the cavity
to
spot
siz
e
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4M cavity test bed at KEK►in 4M ring cavity, photons travel twisted path.
– got geometric phase ●the cavity only resonate w L or R handed
state
– and more,,,
optical feature of the 3D4M cavity is being studied on test bed
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measuring geometry
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a parameter of the 4M cavity
PD
dd
dd
d: keeping circumference constantwhile changing distance between mirrors
smaller d : smaller beam waist
measure beam profile here-->estimate beam size in the cavity
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calculated profile around focal point
z=-4mm z=-2mm z=0
z=0mm z=4mmz=2mm
δ=0.2mm,
focal point
profile is rotating during its propagation!
angular momentum of light
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16
spot size at the center of two focusing mirrors
計算結果
major
minor
smallest with this prototype 2σ=(52μm、 43μm)
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Profile of transmitted light
measurements are consistent with calculation.
find better solution
major axis (calculation)
minor axis (calculation)
major axis (measurement)minor axis (measurement)
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for smaller spot size
plane mirrorplane mirror
concave mirror
concave mirror
major axis minor axis
spot size at focal point
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LAL cavity has been installed to KEK/ATF
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20
Summary• good experience and g ray demonstration
at the ATF with 2 mirror cavity
• progress understanding of 4 mirror ring cavity through prototype construction and calculation
• In near future
setp by step and steady improvement
more complicated but interesting feature of 3D cavity
• bunch by bunch information with 2 M cavity• 4M cavity in the ATF ring
• LAL cavity installed -> prepared for collisions• KEK-Hiroshima type being designed
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More enhancement More precise control
(99.64%, 99.64%) to (99.64%, 99.94%) enhancement: 250 to 760
Witdh of resonant peak got down to 0.35nm from 0.60nm 0.60nm
0.35nm
変更前の共鳴度変更後の共鳴度
cavity length [nm]More precise(~faster) control of cavity
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Resonance
1.2 VPhase
400μs
Feed back system in 2008
Control:Laser to keep resonanceCavity for timing synchronization
Phase mon. PID
Laser
Cavity
Res. Mon.PI
ATF RF
レーザー光
Cont. signal
15ms
RMS~2 ps
Keeping resonance at250 enhacement with timing jitter ~2ps
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制御信号
Initial performance with760 enhancement
RMS~150ps
Faster feed back to laser to keep resonance
位相モニタ PID制御回路
レーザー
蓄積共振器
共鳴モニタPID制御回路
電子 RF
レーザー光
共鳴
timing control could not follow
Larger fluctuation of laser timing
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共鳴
New feedback system
New feedback control+ improve emviromnet
Timing jitter is now < 2ps
Phase Mon PID
Laser
Cavity
Res. Mon.PID
ATF RF
レーザー光
RMS < 2 ps
追加
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at ALCPG09
3D 4M cavity resonates with left and right circular polarizatonseparately
but situation was more complicated
This is due to geometricphase since light travels twistedpath
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Image rotation during light propagation
M(z)=D(L/2).R(θ).F(f2,f1).D(L).R(θ).D(L).R(θ).D(L).R(θ).F(f1,f2).D(L/2)