SummarySummarySession 9BSession 9B

Polarized electron (positron) sources

Session 9B : Polarized electron (positron) sources

Presentationsoral : 15poster : 6

JLAB, SLAC, Univ. of Mainz, Univ. of Bonn, CERN, DESY, St. Petersburg., KEK, Osaka Electro-Communication Univ.,Rikkyo Univ., and Nagoya Univ.,

11 groups

Topics Pol.e- source operation

High average current operation High current density test

Photocathodes Development strained super-lattice photocathode gridded photocathode, pyramidal shape photocathode

Low Emittance Beam Production Polarized electron source for SPLEEM Pol.e± 　 Source for ILC

Polarized electron beam injector Polarized positron beam production

Topics : Pol.e- source operation

Load lock(GaAs on puck)

NEG pipe

Laser(1 W @ 532 nm)

Faraday Cup

High Voltage(100 kV)

Activation(Cs/NF3, 5 mm)

Experimental Setup

350 m 1500 m

Spot SizeAdjustment

High average current test :High average current test : JLAB pol.e- JLAB pol.e- sourcesource

J.Grames (JLAB)

(Best Solution – Improve Vacuum, but this is not easy)

Can increasing the laser spot size improve charge lifetime?

Bigger laser spot, same # electrons, same # ions

electron beam OUT

residual gas

cathodeIonized residual gas strikes photocathode

anode

laser light IN

Ion damage distributedover larger area

J.Grames (JLAB)

Tough to measure >1000 C lifetimes with 100-200 C runs!

5

15

1500350

2≈ 18

Expectation:

High average current test :High average current test : JLAB pol.e- JLAB pol.e- sourcesource

J.Grames (JLAB)

High average current test High average current test Mainz pol.e- source Mainz pol.e- source

Current density is presently limited to 1.6 A/cm2.

57 mA in 100 s long pulses at 100 Hz repetition rate.

Q=5.7 C per Impulse

emitted area *(1.05mm)2~3.5 mm2

hole concentration 2*1019 cm-3

Power, WPower, W 1515

Wavelength, nmWavelength, nm 808 (fixed)808 (fixed)

Pulse length, msPulse length, ms 0.1-100.1-10

Frequency, HzFrequency, Hz 100100

Beam divergence, N.A.Beam divergence, N.A. 0.160.16

K.Aulenbacher (Mainz)

Non-linear effectsNon-linear effects1: Cathode heating

0

0,2

0,4

0,6

0,8

1

1,2

0 50 100 150 200 250

Laser power, mW

Vac

uum

life

time

Photocathode vacuum lifetime normalized to the vacuum lifetime at the laser power 23 mW (>300h) (no current drawn

during ill.).

We are here at

I=1mA (QE=20mA/W)

K.Aulenbacher (Mainz)

Bunch width (FWHM): 1.6ns Bunch charge : 8nCLaser spot size :~20mm,

Peak current density ~18 mA/mm2

　 No Charge Limit

bunch charge : 3.3pC/bunch

Laser Spot size~1.6mm(2) 　

bunch width : ~30ps (estimate)

Peak current density (estimate) :

~240 mA/mm2

High current density testHigh current density test Nagoya pol.e- source Nagoya pol.e- sourceM.Yamamoto (Nagoya)

Load-lock gun operation at Load-lock gun operation at Univ.BonnUniv.Bonn

P = 80% @ 830 nmQE = 0.2 %

M.Eberhardt and J.Wittschen(Bonn)

New Load-Lock at New Load-Lock at Univ.BonnUniv.Bonn

M.Eberhardt and J.Wittschen(Bonn)

Topics : Photocathodes Development

Composition Thickness Doping

As cap

GaAs QW 60 A 71018 cm-3 Be

Al0.36Ga0.64As

SL

23 A

31017 cm-3 BeIn 0.155Al 0.2Ga 0.645As

51 A

Al0.4Ga0.6As Buffer 0.3 m 61018 cm-3 Be

p-GaAs substrate

MBE grown InAlGaAs/AlGaAs strained-well superlattice

Eg=1.543eV, Valence band splitting Ehh1 - Elh1 = 60 meV, Pmax=92%, QE=0.6%.

Y.Mamaev (St.Petersburg)

550 600 650 700 750 800 850 900

10-5

10-4

10-3

10-2

10-1

100

101

0

20

40

60

80

100

QEQ

E,

%

, nm

Polarization

Pol

ariz

atio

n,

%

SL In0.155Al 0.2Ga0.645As(5.1nm)/Al0.36Ga0.64As(2.3nm), 4 pairs

Y.Mamaev (St.Petersburg)

The optimization of DBR – superlattice structures is underway.

polarization(max.) : 92%, Quantum efficiency : 0.6%

Material specific depolarizationMaterial specific depolarization

emitemit = 3-5 ps (Mainz)= 3-5 ps (Mainz) If If ss < 35 ps, the spin relaxation time has a significant effect on < 35 ps, the spin relaxation time has a significant effect on

polarization.polarization. D’yakonov-Perel (DP) mechanism is dominant in low doped SL.D’yakonov-Perel (DP) mechanism is dominant in low doped SL.

DP mechanism comes from the spin-orbit interaction.DP mechanism comes from the spin-orbit interaction. Find materials with a smaller spin-orbit interaction.Find materials with a smaller spin-orbit interaction. GaN GaP GaAs GaSbGaN GaP GaAs GaSb SO SO (eV) 0.01 0.08 0.34 0.76(eV) 0.01 0.08 0.34 0.76 Try GaAs/InGaP strained-superlatticeTry GaAs/InGaP strained-superlattice

0PPPemits

sBBR

PP00: Initial polarization: Initial polarization ss : spin relaxation time : spin relaxation time emitemit : photoemission time : photoemission time PPBBRBBR: depolarization at BBR: depolarization at BBR

T.Maruyama (SLAC)

Spin relaxation rate based on Spin relaxation rate based on D’yakonov-Perel mechanismD’yakonov-Perel mechanism

: spin-orbit-induced spin splitting coefficient: spin-orbit-induced spin splitting coefficient EE1e1e: confinement energy: confinement energyp

eB

s

ETmk

5

21

3* )(161

Narrower well has a larger confinement energy.Narrower well has a larger confinement energy. Larger confinement energy Larger confinement energy

Less vertical transport, thus lower QELess vertical transport, thus lower QE More scattering, thus lower polarization. More scattering, thus lower polarization.

s ~ 10 pss ~ 2 ps

T.Maruyama (SLAC)

Superlattice structure affects dramaticallySuperlattice structure affects dramatically

1.5 nm GaAs + 4 nm In0.65Ga0.35P 4 nm GaAs + 1.5 nm In0.65Ga0.35P

QE ~ 0.002%Pol ~ 40%

QE ~ 0.01%Pol ~ 68%

T.Maruyama (SLAC)

Structure of gridded cathodeStructure of gridded cathode

Composition Thickness Doping

p- GaAs substrate, 5x1018cm-3 Zn doped

Al.3Ga.7As buffer 5x1018cm-3 Be doped

GaAs,AlGaAs,GaAsP/GaAsactive region 90nm 1014 - 1018 cm-3 Be doped

GaAs surface region 5-10nm 1- 5x1019cm-3 Be doped

MBE grown high surface/low

active doping gridded cathode

0.3um W film, Ohmic contact

Metal grid, Schottky contact

K.Ioakeimidi (SLAC)

Thin GaAs films with 4mm 2D grid and 48mm pitch Thin GaAs films with 4mm 2D grid and 48mm pitch

QE&Polarization - gridded samplesQE&Polarization - gridded samples

5x1016cm-3

K.Ioakeimidi (SLAC)

Monte Carlo simulations indicate that the QE-Polarization trade off can be broken by accelerating the electrons in the active region Preliminary experimental results indicate a 1% increase in polarization

M.Kuwahara (Nagoya)

Pol.e- extraction from Pyramid-shaped Photocathode

Extraction of polarized electrons by F.E.

Electrons extracted by F.E. have higher polarization than NEA’s.

long lifetime compared with NEA surface.

Topics : Low Emittance Beam Production

Low Emittance Beam extraction from GaAs-GaAsP superlattice photocathode

N.Yamamoto (Nagoya)

Low Emittance Beam extraction from GaAs-GaAsP superlattice photocathode

rms : 0.096±0.015 .mm.mradN.Yamamoto (Nagoya)

Topics : Polarized electron source for SPLEEM

Yasue (Osaka Elec.Comuni.Univ)

ReflectionDiffraction

sample

ElectronsLow energy electrons: strong interaction with surfaces - relatively high reflectivity - small penetration depth

SURFACE SENSITIVE

energy filter

electron optics

manipulator

20cm

CCD camera

sample

objectivelens

beamseparator

energyfilter

screen

e- source

HV

LEEM (Low Energy Electron Microscopy)

Co/W(110) 3.8eV FOV=25m in-plane

=0o =45o =90o=-45o=-90o

MM

P

M

CONTRAST: P·MP // M: maximum (minimum)

P M: 0

Yasue (Osaka Elec.Comuni.Univ)

Spin Polarized LEEM (SPLEEM)

Exchange Asymmetry A

II

II

P

1A

II

IISPLEEM Contrast: P HIGH POLARIZATION

FAST ACQUISITION OF SPLEEM IMAGE

For higher magnificationFor much faster acquisition

HIGH BRIGHTNESS (HIGH INTENSITY) SOURCE

Yasue (Osaka Elec.Comuni.Univ)

S.Okumi (Nagoya)

focusing length ~ 4mm

spot size ~ 3m

Concept of extracting high brightness beam

S.Okumi (Nagoya)

Topics : Pol.e± 　 Source for ILC

0

200

400

600

800

1000

0 100 200 300 400 500 600

Longitudinal position (cm)

Pha

se in

L-b

and

deg

(FW

HM

)

2nd SHB

1st SHB

L-band buncher

6.4 nC, 2 ns

ILC e- injectorILC e- injectorwith SLC gun and drift distance to SHB1with SLC gun and drift distance to SHB1

7575 202 33

20 bend

DC gun

SHB1 SHB2 Two 5-cell L-band

10 20 5

Two 50-cell NC L-band pre-acceleration

All units in cm

… …

J.E.Clendenin (SLAC)

ParameterParameter UnitsUnits At gun exit

After bunchers*

ChargeCharge nCnC 6.4 6.2

Bunch length Bunch length (FWHM)(FWHM)

pspsDeg. L-bDeg. L-bandand

2000932

146.8

Energy/Energy Energy/Energy spreadspread

MeVMeV 0.12 9.5/0.09(0.95%)

Normalized rms Normalized rms emittanceemittance

1010-6-6 m m n/a 43

PARMELA results

M.Yamamoto (Nagoya)

Solenoid

4.8nC,16mm

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

z [m]

-15

-10

-5

0

5

10

15

x [m

m]

0 0.15 0.5[m]

anode

Solenoid

200kV,1.0ns,4.8nC

SHB1 SHB2

0 1.0 3.0 3.4[m]

108MHz 433MHz

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Position [m]

0

20

40

60

80

100

120

bu

nch

len

gth

(rm

s) [

mm

]

200keV,4.8nC,1.0ns

Similar geometry of TESLA 2001-22 (Aline Curtoni et al).

rms ~ 9.7 pi.mm.mrad

Beam Simulation (Nagoya 200keV Gun)

A.Brachmann (SLAC)

Schematic Layout

A.Brachmann (SLAC)

Two 5-cell SW L-band108MHz SHB

433 MHz SHB 1st TW Structure 2nd TW Structure

matching triplet

Low Energy Beam Line and Bunching System Simulations including Space Charge

Spin Rotation using Spin Rotation using SolenoidsSolenoids

bendspin

GeVE *44065.0

)( T

B

dlBzspin 26

*0

5 GeV

Bend of n * 7.9312o

Odd Integer

Slongitudonal

~ 7.5 m

DR

Pair of Solenoids (SC)

Svertical

(Precession)

Stransverse

(Rotation)

ILC design: n = 7 55.51o

Depolarization in arc due to energy spread:

cos1

P

P

Arc bending angle θ = 55.51o

Spin precession angle =(7/2)Energy spread Δ/ = ±0.02 GeVDepolarization (analytic) ΔP/P = 0.024Particle tracking ΔP/P = 0.007

A.Brachmann (SLAC)

T.Omori (KEK)

Laser-Based Polarized ee++ Source for ILC

A = 0.90 ± 0.18 % Pol. = 73 %

M. Fukuda et al., PRL 91(2003)164801

T.Omori (KEK)

Electron storage ring

laser pulse stacking cavities

po

sitron

stacking

in m

ain D

RRe-use Concept

Compton ring

to main linac

T.Omori (KEK)

P.Shuler (DESY)

The E166 Experiment

P.Shuler (DESY)

Pol.e+ (max.) : ~80%