Laser/cavity R&D for a polarised positron source
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Laser/cavity R&D for a polarised positron source
Outline •Introduction•Goal of the R&D•Status•Futur
Collaborating Institutes:Hiroshima, KEK, LAL
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Up to 300 MHz
300 MHz
Up to300 MHz
Former goal : Compton based polarised positron source for ILC now a generic R&D on high flux [monchromatic] soft X-rays source e.g. production of 78keV X-rays for radiotherapy for brain cancer (glioblastom)
Goal(s) of the R&D
Optical resonator required to reach high average pulsed laser power
T. Omori
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K. Moenig idea to modify the KEK schemeILC beam = trains of~3000 bunchs
•AND Train frequency =5Hz
100ms to create & 100ms to cool
the polarised e+
Introduction : e+ polarised source for the ILC
The original idea : the KEK scheme
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10 of 600mJ Optical Cavities
ERL scheme for the e+ polarised source (proposed by A. Variola)
0.6J/pulse@1ps@60MHz <P>=36MW !!!For 1 cavity R&D ! (KEK, LAL)
1-3nc/bunches… R&D at Cornell& KEK
Kuriki-san
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1ps Pulsed laser
Fabry-Perot cavitywith Super mirrors
Electron beam
R&D tasks on Fabry-Perot in 1ps pulsed regime: •Accelerator implementation & operations• Max. power gain (=enhancement factor) achievable [published : gain 200/120fs in 2007 & gain 6000/30ps at SLAC]•Minimisation of laser beam spot size to optimize Compton X-section
Laser/cavity R&D to reach 600mJ/pulse@~100 MHz
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Complementary R/D in LAL and in KEK
Very High Enhancement ~ 20000-100000R/D in LAL
Moderate Enhancement ~ 1000R/D in KEK
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Very High Enhancement ~ 20000-100000Small spot size ~ 10 micron
R/D in LAL
Moderate Enhancement ~ 1000Moderate spot size ~ 30 micron
R/D in KEK
Complementary R/D in LAL and in KEK
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Very High Enhancement ~ 20000 - 100000Small spot size ~ 10 micronSofisticated cavity stucture with 4 mirrors
R/D in LAL
Moderate Enhancement ~ 1000Moderate spot size ~ 30 micronSimple cavity stucture with two mirrors
R/D in KEK
Complementary R/D in LAL and in KEK
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Very High Enhancement ~ 20000 - 100000Small spot size ~ 10 micronSofisticated cavity stucture with 4 mirrors
R/D in LAL
Moderate Enhancement ~ 1000Moderate spot size ~ 30 micronSimple cavity stucture with two mirrors
R/D in KEK
Digital feedback
Analog feedback
Complementary R/D in LAL and in KEK
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R&D at KEK : Cavity installation on the Accelerator Test Facility (ATF)
~ 54 m
~
30 m
Beam Energy
→ 1.28GeV
Beam Size
→ 100μm×10μm
Emittance →
1.0x10-9 rad.m
1.0x10-11 rad.m
(Ultra Low !!)
(H. Shimizu)
.cavity
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R&D Report in ATF
Laser Section Type YAG-VAN (1064nm) Power 10 W Frequency 357 MHz Pulse Width 10 psCavity Section Length 420 mm Mirror Reflection Coeff.
99.7 %
Beam Waist 60 μm ( in 2σ) Crossing Angle 12 degree
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ATF e-Beam
LaserLaser
Port for ion pumpPort for ion pump
Terminal for piezo
Micro-positioning system
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Laser
e-Beam
Mirror housing
Piezo housing
12deg.
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Status :•Cavity received•Enhancement ~ 1000•Feedback under studies•Installation automn 2007
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T. Udem et al. Nature 416 (2002) 233
R&D at LAL : toward very high power enhancement
Difficulty = properties of passive mode locked laser beams
Frequency comb all the combmust be locked to the cavity Feedback with 2 degrees of freedom : control of the Dilatation & translation
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1 W Ti:sa laser1ps@frep=76MHz
vacuum cavity
R&D setup at LAL/Orsay
Status : Cavity locked (low gain ~1200)•Digital feedback (VHDL programming) set up•Already frep/frep=10-10 frep=30mHz for frep=76MHz•New mirrors in septembre gains 104-105
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Small laser spot size &2 mirrors cavity unstable resonator (concentric resonator)
BUT astigmatic & linearly polarised eigen-modes
Stable solution: 4 mirror cavity as in Femto lasers
Non-planar 4 mirrors cavityAstigmatism reduced & ~circularly polarised eigenmodes
R&D at LAL : toward small laser spot size
e- beam
Laser input
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3D cavity prototype
Cw laser diode inextended cavity config(Littrow configuration)
Y. Fedala
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3D cavity modes
Exp. Higher order Modes
Th. results
Eigenmodes well described (shape and size)~10m spot size achieved (limited by mirror edge diffraction) mechanical stability measured
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e- beam tube
Vacuum chamber Support
beam Support
Length 1.5m/2
tube diameter : 420 mm
4 mirrors cavity design for ATF
R. Cizeron
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Spherical mirrors
3 Beam supports
Flat mirror
Flat mirror
Invar ( Fe-Ni alloy)
12 moteurs ‘encapsulated’ inside vaccum
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Mirrors holders design study
3 piezos
θx & θy
motor
actuator θy
Z displacement
motor
actuator θx
Builded & tested at LAL
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Futur: toward higher incident laser power
• Presently the laser average power is– 10W at KEK– 0.7W at Orsay
• Laser R&D– LAL : 150W average power (1ps@190MHz)
• Started in june 20072008• Installation at ATK with 4 mirrors cavity
– KEK & LAL : • 150WkW level after 2008
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Laser Diode Laser Diode
40/170 40/170
Gold grating-based strectcher
OI
150 fs, 73 MHz
1W
High average power system
Femtosecond oscillator
Grating stretcher
CompressorFiber amplifiers
Doped photonic fibre :Large core diameter (up to 100m !!!)& monomode..
F. Röser et al. Optics letters, 30, p2754, 2005
Max published
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•For most of laser applications : Interests for high peak power, not for high average power and/or femto pulses we have to do laser R&D ourselves for high repetition rate and 1ps
Evolution of continuous wave fibre laser power
“4.8kW average power may be(hardly) achievedIn the future” [131W today…]
Photonic fibre is a very recent promising technology …
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Summary• R&D on high flux soft X-rays based on
Laser-e beam Compton scattering– Complementary R&D at KEK & LAL
• 2 mirrors & moderate enhancement ~1000 installed at ATF/KEK– Very high enhancement factor studies at LAL & non planar
resonator conception/construction• New high average power laser source KEK/LAL R&D
started– Needed to reach the required X-rays rate
• ~1-10Mw average power inside cavity expected • = 20-200GW peak power• =8-80mJ/pulse
• Would this help for the Photon Linear Collider ?– Much more pulse power needed…
non-linear & thermal effects in the mirror coatings ? huge cavity size
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Backslides
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1 Feb 2007 IHEP, China ILC e+ source R&D Group 29
Yield Evaluation• 1.5x109 electrons/bunch generates
8.2x108 /collision.• 10 collisions make 8.2x109 /bunch total,
2.4x109 /bunch in effective energy range.• Assuming 0.3% efficiency for e+ conversion
and capture, 7.5x106 e+/bunch is obtained.• This bunch train continues 100ms with 6.2ns
spacing.• # of revolutions of DR(C~6.7km) in 100ms is
4000. Top-up injection up to 4000 bunches in a same bucket make 3.0x1010 e+/bunch.
• Another 100ms is for damping
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1 Feb 2007 IHEP, China ILC e+ source R&D Group 30
Yield Evaluation (2)Energy spread after IRs (ERL)
Energy spread after IRs (CR)
By E. Bulyak
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Cardan (gimbal)
3 piezos at 120°
membrane to support mirror
piezoØ 1 inch
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Une application médicale à l’ESRF (ligne ID17): radiothérapie pour le traitement des gliomes
Pas de traitement pour le ‘glioblastome’ aujourd’hui (& 7 cas/105 par an…) :•Idée (cf these S. Corde, J.F. Adam, ESRF)fixer un élément lourd (platine) sur l’ADN cancéreuse puis exciter l’atome par un rayonnement X (78 keV=couche K) pourdétruire cette ADN…
Sélection de l’énergie
du rayonnement
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Pourquoi du rayonnement synchrotron ?
Pourquoi un élément à grand Z (le platine)
Haut flux de X monoénergétiques à 78 keV Parcourt moyen de ces X dans l’eau convenable
Minimisation des pertes dans les tissus sains &
maximisation de l’effet radiotérapeuthique
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Cis-platine + rayons 78keV
Résultat [MC Biston et al. cancer reas. 64 (2004)2317]
Source rayons X Monoénergétique
nécessaire
ESRF (Grenoble)
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Nécessité aussi d’une machine à bas coupUtilisation de l’interactionCompton (e-+laser → e- + photon)Laser pulsé ‘amplifié’ dans unecavité Production de rayons X dont onpeut choisir l’énergie (=longueurd’onde) à des flux de puissance tolérables par l’organisme