Upload
kobe
View
40
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Summary Session 9B. Polarized electron (positron) sources. Session 9B : Polarized electron (positron) sources. Presentations oral : 15 poster : 6. 11 groups. JLAB, SLAC, Univ. of Mainz, Univ. of Bonn, CERN, DESY, St. Petersburg., KEK, Osaka Electro-Communication Univ., - PowerPoint PPT Presentation
Citation preview
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%