Polarized Positron Source using Backward Compton Scattering
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Transcript of Polarized Positron Source using Backward Compton Scattering
T.Takahashi Hiroshima 1
2007/11/5
Tohru TakahashiHiroshima University
高橋 徹広島大学
T.Takahashi Hiroshima 2
Why polarized positrons
Le
Re
/Z Le
Re
W
W
electrons are polarized,,,,,, choose helicity of its counter part
if unpolarized e+
a half of the beam is thrown away
T.Takahashi Hiroshima 3
electon beam is polarized but,,,,
Re
/R Le
W
W
In principle, we can suppress this by polarized electrons if we want but
( )P e
1e e
eff
e e
P PP
P P
0( ) 100%P e
( ) 80%P e ~ 95%
( ( ) 0.6)
effP
P e
polarization (either e- or e+) has to be well controlled
Positron polarization
Positron polarization helps much to :
increase luminosity effectively suppress background
physics is sensitive to the polarization
ILC: e+ Polarization from Beginning?
To use the e+ polarization for physics we strongly ask to provide a machine with flexible helicity reversal also for the positron beam
No or very rare reversal of e+ helicity could be worse than no e+ polarization
Positron Pol WG
Reminder: Positron Pol is important for numerous physics channels
•Gain in production rate•Reduction of Bckgrnd•Access to new channels
J.Hewett LCWS07 SUSY, New Phys. summary
How to get them
e
e
Helical Undulator
Ee~150GeV
L>150mEe~GeV
LaserCompton
(10 )O MeV
T.Takahashi Hiroshima7
pros and consCompton
based positron polarization
• independent of main linac
• good capability of controlling polarization
•R& D issues•how to get enough intensity
T.Takahashi Hiroshima 8
Proof of Principle at KEK - ATF
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To meet ILC requirements
Requirements for ILC
•2x1010/bunch•~3000 bunches/train•5Hz
ideas to meet requirement
•Single pass•Linac based
•Recycling e- and Lasers•e- Storage ring + optical cavity•Energy Recovery Linac(ERL) + optical cavity
Linac Scheme
T.Takahashi Hiroshima 10
4GeV, 1A
15MeV e+
Co2 laser 1J Single pass 5x1011 2x1010 e+
V.Yakimenko~2m
115 10 102 10 e
directly creates enough e+
high current e- source, regenerative laser cavity?
capturesystem
Compton Ring Scheme
T.Takahashi Hiroshima 11
1.3 GeV e- source
Electron Storage Ring
Optical Cavities
target
dam
pin
g rin
g
main linac
6.15ns
electron bunches stored in the ringlaser pluses are stacked in the optical cavities -> 600mJ stacking 100 bunches on a same bucket in the DR -> 2.4x1010 e/bunch
2.4x108 e+1.7x1010
high repetion e- source
optical cavity, pulse staking, e- quality in ring?
capturesystem
ERL Scheme
T.Takahashi Hiroshima 12
e- gun
Energy Recovery Linac
Optical Cavities
target
dam
pin
g rin
gmain linac
6.15ns
get fresh e bunches by ERL laser pluses are stacked in the optical cavities -> 600mJ continues stacking ~1000 bunches on a same bucket in the DR -> 2x1010 e/bunch
2x107 e+6.4x109
dump
high repetition e-, fresh e- each turn, higher pol.
optical cavity, ERL, bunch stacking?
CR/ERL simulations studies (Kharkov, LAL, JAEA, KEK)design studies
Optical Cavity (LAL,IHEP, Hiroshima, KEK)
e+ capture (LAL, ANL)We will start collaboration with KEKB upgrade study
e+ stacking in DR (CERN)Basic beam dynamics studies
LaserFiber laser / Mode-lock laser (cooperation with companies)CO2 laser (BNL)
experimental R/D
beam dynamics studies
omoriR&D times
325 MHz
325 MHz
Cavity Enhancement Factor = 1000 - 105
Laser-electronsmall crossing angle
Laser bunches
Lcav = n Lcav = m Llaser
Omori
Laser pulse stacking cavity
4-mirror cavity (LAL)
2-mirror cavity (Hiroshima/KEK)
high enhancementvery small spot sizecomplicated control
moderate enhancementsmall spot sizesimple control
Prototypes
accumulate experiences w/ beamat ATF
to ATF later
Experimental R/D at ATF
ATF atKEK
•2 mirror FP•Lcav = 420 mmfor 2.8ns bunchspacing
installed into the ATF DR last September
World-Wide-We b of Laser Compton
T.Takahashi Hiroshima
Pulse Stacking Cavity for colliders
K. Moeing
•100 m long pulse stacking cavity surrounding the detector
opticalcavity for collisers = (pluse + small spot size + high power) + (larger scale)
~ polarized positron + gravitational wave
Summary Polartized Positron is useful and
preferable to be implemented at the early stage of the ILC
Laser-Compton scheme looks attractive
Many common efforts can be shared in various applications.
State-of-the-art technologiesLaser, Optical cavities,ERL
Stay tuned and Join us
25/05/2007 POSIPOL 2007
21
e- beam tube
beamInteraction
pointe- beam
4 mirror cavity at LAL
intend to be installed into ATF
T.Takahashi Hiroshima 22
Proof of Princple at KEK - ATF
Pros and Cons
T.Takahashi Hiroshima 23
Linac SchemeHigh gen by one pass; no stacking in DR10nc 5ps e- sourcehigh power Co2 laser: regenerative cavity
Ring Comptonmoderate laser power w/ optical cavity100 stackingoptical cavity R&Dbeam life, stability on the Compton Ring Crab crossing?
ERLmoderate laser power w/ optical cavityhigh yield /w stackinghigher polarization200 ~ 1000 staking optical cavity R&DEnergy recovery after compton
Optical cavity bunch stacking seems
CO2 Laser system for
ILC
intra-cavity pulse circulation :– pulse length 5 ps– energy per pulse 1 J– period inside pulse train 12 ns– total train duration1.2 s– pulses/train 100– train repetition rate 150 Hz
– Cumulative rep. rate 15 kHz– Cumulative average power 15 kW
Kerr generator
IP#1 IP#5
2x30mJ
CO2 oscillator
10mJ 5ps from YAG laser
200ps
1J 5ps
10mJ5ps
300mJ 5 ps
TFPPC PC
150ns Ge
1J
e-
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Positron Sources
Polarized Electron sourcePositron Source
electron positron
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Pros and Cons
ComptonHelical Undulator
Indepedence
need 150GeV e- from main linace
independent of main linac
Tunabilityneed deceleration for low energy operation
Pol. flipnot foreseen yet no problem
no problem
e+ intensityOK? intense
bunch stacking
T.Takahashi Hiroshima 27
Principle of Pol. e+ generationby Compton Scattering
Omori
e
(~ )e GeV
laser