Transcript Polarized positron source using

Tohru Takahashi
Hiroshima University
高橋 徹
広島大学
2007/11/5
T.Takahashi Hiroshima
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Why polarized positrons

L
e
W

L
e
Z /

R
e
eR

W
electrons are polarized,,,,,,
 choose helicity of its counter part
if unpolarized e+
a half of the beam is thrown away
T.Takahashi Hiroshima
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electon beam is polarized but,,,,
W

R
e
eR / L


P(e )
P(e )  80%
0
W
Peff 
In principle,
we can suppress this by
polarized electrons
if we want but
P(e )  100%
Pe  Pe
1  Pe Pe
Peff ~ 95%
( P(e )  0.6)
T.Takahashi Hiroshima
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Positron polarization
Positron polarization helps much to :
increase luminosity effectively
suppress background
physics is sensitive to the
polarization
polarization (either e- or e+) has to be well controlled
J.Hewett LCWS07 SUSY, New Phys. summary
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
Reminder: Positron Pol is
important for numerous physics
channels
•Gain in production rate
•Reduction of Bckgrnd
•Access to new channels
Positron Pol WG
How to get them
Laser
Compton
Helical Undulator
Ee~GeV
Ee~150GeV
L>150m
O(10MeV ) 
e
e
pros and cons
Compton
based positron polarization
• independent of main linac
• good capability of controlling polarization
•R& D issues
•how to get enough intensity
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T.Takahashi Hiroshima
Proof of Principle at KEK - ATF
T.Takahashi Hiroshima
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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
T.Takahashi Hiroshima
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Linac Scheme
 Co2 laser 1J
Single pass 5x1011   2x1010 e+
4GeV, 1A
5 1011
2  1010 e 
15MeV e+
~2m
directly creates enough e+
V.Yakimenko
? high current e- source, regenerative laser cavity
T.Takahashi Hiroshima
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Compton Ring Scheme
electron bunches stored in the ring
laser pluses are stacked in the optical cavities -> 600mJ
 stacking 100 bunches on a same bucket in the DR -> 2.4x1010 e/bunch
target
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capture 2.4x10 e+
system
1.7x1010 
Electron Storage Ring
1.3 GeV
e- source
high repetion e- source
damping ring
Optical Cavities
main linac
? optical cavity, pulse staking, e- quality in ring
T.Takahashi Hiroshima
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ERL Scheme
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
target
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6.4x10 
capture 2x10 e+
system
Energy Recovery Linac
main linac
damping ring
Optical Cavities
e- gun
dump
high repetition e-, fresh e- each turn, higher pol.
? optical cavity, ERL, bunch stacking
T.Takahashi Hiroshima
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R&D times
omori
CR/ERL simulations studies (Kharkov, LAL, JAEA, KEK)
design studies
beam dynamics studies
Optical Cavity (LAL,IHEP, Hiroshima, KEK)
experimental R/D
e+ capture (LAL, ANL)
We will start collaboration with KEKB upgrade study
e+ stacking in DR (CERN)
Basic beam dynamics studies
Laser
Fiber laser / Mode-lock laser (cooperation with companies)
CO2 laser (BNL)
Laser pulse stacking cavity
Laser-electron
small crossing angle
Omori
Laser bunches
325 MHz
325 MHz
Lcav = n 
Lcav = m Llaser
Cavity
Enhancement Factor = 1000 - 105
Prototypes
4-mirror cavity (LAL)
high enhancement
very small spot size
complicated control
to ATF later
2-mirror cavity (Hiroshima/KEK)
moderate enhancement
small spot size
simple control
accumulate experiences w/ beam
at ATF
Experimental R/D at ATF
•2 mirror FP
•Lcav = 420 mm
for 2.8ns bunch
spacing
ATF at
KEK
installed into the ATF DR
last September
World-Wide-We b of Laser Compton
Pulse Stacking Cavity for  colliders
•100 m long pulse
stacking cavity
surrounding the detector
opticalcavity for  collisers =
(pluse + small spot size + high power) + (larger scale)
~ polarized positron + gravitational wave
T.Takahashi Hiroshima
K. Moeing
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 technologies
 Laser, Optical cavities,ERL
Stay tuned and Join us
4 mirror cavity at LAL
e- beam
Interaction
point
beam
e- beam tube
intend to be installed into ATF
25/05/2007
POSIPOL 2007
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Proof of Princple at KEK - ATF
T.Takahashi Hiroshima
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Pros and Cons
Linac Scheme
High  gen by one pass; no stacking in DR
10nc 5ps e- source
high power Co2 laser: regenerative cavity
Ring Compton
moderate laser power w/ optical cavity
100 stacking
optical cavity R&D
beam life, stability on the Compton Ring
 Crab crossing?
ERL
moderate laser power w/ optical cavity
high  yield /w stacking
higher polarization
200 ~ 1000 staking
optical cavity R&D
Energy recovery after compton
T.Takahashi Hiroshima
Optical cavity
bunch stacking
seems
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Kerr generator
CO2 Laser
system for
ILC
200ps
150ns
Ge
1J
5ps
PC
CO2 oscillator
PC
TFP
10mJ
5ps
10mJ 5ps
from YAG laser
300mJ 5 ps
2x30mJ
intra-cavity pulse circulation :
– pulse length
– energy per pulse
– period inside pulse train
– total train duration 1.2 s
– pulses/train
– train repetition rate 150 Hz
5 ps
1J
12 ns
1J
100
– Cumulative rep. rate15 kHz
– Cumulative average power 15 kW
IP#1
e-
IP#5

Positron Sources
electron
positron
Polarized Electron source
Positron Source
T.Takahashi Hiroshima
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Pros and Cons
Helical Undulator
Compton
need 150GeV e- from
main linace
independent of main linac
need deceleration for
low energy operation
no problem
not foreseen yet
no problem
OK?
intense 
bunch stacking
Indepedence
Tunability
Pol. flip
e+ intensity
T.Takahashi Hiroshima
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Principle of Pol. e+ generation
by Compton Scattering
laser
e (~ GeV )

e
Omori
T.Takahashi Hiroshima
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