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

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Proof of Principle at KEK - ATF

T.Takahashi Hiroshima 9

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