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Brookhaven Science AssociatesU.S. Department of Energy
Brookhaven Science AssociatesU.S. Department of Energy
A Few Comments on the Photoinjector Performance
X.J. WangNational Synchrotron Light SourceBrookhaven National Laboratory
Upton, NY 11973, USA
Presented at the UCLA High-Power Brightness Beams WorkshopNov.9, 2004
Brookhaven Science AssociatesU.S. Department of Energy
AcknowledgementAcknowledgement
I would like to thank many colleague who have educated me over many years on various subjects I mentioned here,
BNL: M. Babzien, K. Batchelor, I. Ben-Zvi, X.Y. Chang, A. Doyuran, J. Fisher, W. Graves, H. Loss, J. Murphy, T. Rao, J. Rose, B. Sheehy, J. Sheen, Z. Wu, V. Yakimenko and L.H. Yu
ANL: S. Biedron, M. Conde, W. Gai, J. Lewellen, S. Milton, J. Power
SLAC: R. Miller, D.T. PalmerJapan: A. Endo, K. Kobayashi, F. Sakai, J. Urakawa, Uesaka and
M. Washio
And Many others. Thank you!
Brookhaven Science AssociatesU.S. Department of Energy
BNL NSLS PERL Gun Workshop (1/2001)BNL NSLS PERL Gun Workshop (1/2001)
• High QE Green or Red Cathode.
• 2 ½ Cell low temperature RF gun
•DC and RF gun both capable of CW operation.
Dc: 10 mm-mrad
RF: 1.0 mm-mrad
Brookhaven Science AssociatesU.S. Department of Energy
Challenges in High-Brightness Electron Source R&D
Challenges in High-Brightness Electron Source R&D
• Stability and Reliability• Timing jitter and its control• Better Theoretical Understanding• Thermal Emittance – fundamental limit and
importance of beam instrumentation• Improve performance – 6-D optimization• Next Generation Electron source:1. CW injector –DC, RF, SRF, what should be? 3H -
Heat, Heat and Heat;2. Brighter sources - Higher field gun, pulse DC
gun, laser plasma source and others.
Brookhaven Science AssociatesU.S. Department of Energy
High Brightness Electron InjectorsHigh Brightness Electron Injectors
500 kV Spring-8 DC Injector
How to create the Greenfield FEL injector?
• Optimize 6-D phase space, not just Optimize 6-D phase space, not just nn or I or Ip p
• To realize this the GFEL injector should To realize this the GFEL injector should achieve:achieve:
G > 500 MV/m , E > 50 MeV
in order to produce and preserve the beam.
Type DC Gun RF Gun GreenField
E [MeV] 0.5 5 5050G[MV/m] 10 100 500500 [ps] 500 10 <1Ip [A] 10 100 500Q [nC] 0.5 1 <0.5n [m] 1 1 0.1
BNL RF Photoinjector
Brookhaven Science AssociatesU.S. Department of Energy
Brookhaven Science AssociatesU.S. Department of Energy
XFEL vs Linear Collider
M. Brandin et al, CLIC Note 543 (2002)
Brookhaven Science AssociatesU.S. Department of Energy
ISSUESISSUES
•Introduction – What are the performance and Applications
•Vacuum and QE do Matter. •6-D Performance Optimization •Thermal Emittance•Timing Jitter – What is required?•Theoretical Challenges of RF Gun •Femto-second Kilo-Ampere Electron
Beam Generation - Longitudinal Emittance Compensation
Brookhaven Science AssociatesU.S. Department of Energy
They all driven by a photocathode RF Gun Based Linac
They all driven by a photocathode RF Gun Based Linac
Brookhaven Science AssociatesU.S. Department of Energy
IntroductionIntroduction
All the FEL reach saturation does not test the limit of the emittance performance:
1. LEUTL and TTF I < 6-10 mm-mrad2. VISA <2.0 - 2.5 mm-mrad3. DUV-FEL < 5 mm-mra
Does Any Physics Experiment Test the limit:1. Laser Compton Scattering < 2 mm-mrad2. IFEL Micro-bunching - Stella Experiment <
1-2 mm-mrad
Brookhaven Science AssociatesU.S. Department of Energy
Why Photocathode RF Gun
Why Photocathode RF Gun
• 6-D performance – smaller emittance and shorter bunch.
• Flexibility.
But it bring more issues, mainly laser and cathode:
• Stability • Reliability• Uniformity – QE, transverse and
longitudinal distribution• Jitters – position and time
Brookhaven Science AssociatesU.S. Department of Energy
Vacuum and QE Do Matter
Vacuum and QE Do Matter
(at Room Temperature)
Pressure(Torr)
Molecular Density(molec./cm3)
Molecular Incidence(molec./cm2sec)
Mean FreePath(cm)
MonolayerFormation Time
(sec)
760 2.49 x 1019 2.87 x 1023 3.9 x 10-6 1.7 x 10-9
1 3.25 x 1016 3.78 x 1020 5.1 x 10-3 2.2 x 10-6
10-3 3.25 x 1013 3.78 x 1017 5.1 2.2 x 10-3
10-6 3.25 x 1010 3.78 x 1014 5.1 x 103 2.2 x 100
10-9 3.25 x 107 3.78 x 1011 5.1 x 106 2.2 x103 (37 min)
10-12 3.25 x 104 3.78 x 108 5.1 x 109 2.2 x 106 (25.5 days)
Brookhaven Science AssociatesU.S. Department of Energy
Laser-Induced Explosive Emission(X.J. Wang et al, J. Appl. Phys. 72(3), 888-894 (1992))
Laser-Induced Explosive Emission(X.J. Wang et al, J. Appl. Phys. 72(3), 888-894 (1992))
Brookhaven Science AssociatesU.S. Department of Energy
What We would like Photoinjector doWhat We would like Photoinjector do
Programmable in both transverse and longitudinal distribution
•No timing jitter
•No energy fluctuation
•Perfect point stability
•7/24 available
•Remote controllable
•NO laser physicist.
rms peak
Timing jitter 50 - 100, fs 200 - 400, fs
energy 1,% 5,%
Point stability 0.25, 1,%
Transverse uniformity
2.5,% 10,%
Brookhaven Science AssociatesU.S. Department of Energy
Photo-injector Beam Diagnostics
•Energy
•Charge
•RF Gun Phase
150 160 170 180 190 200 210 2203.8
3.9
4
4.1
4.2
4.3
4.4
4.5
Relative RF Gun Phase (deg.)
Pho
toel
ectr
on B
eam
Ene
rgy
(MeV
)
Brookhaven Science AssociatesU.S. Department of Energy
Quantum Efficiency MeasurementsQuantum Efficiency Measurements
0 2 4 6 8 10 12 140.5
1
1.5
2
2.5
3
3.5
Laser Energy ( J)
Ph
oto
ele
ctro
n C
ha
rge
(n
C)
Ocotober, 1999March, 2002
Brookhaven Science AssociatesU.S. Department of Energy
Stability and Reliability Leads To Better Performance
Brookhaven Science AssociatesU.S. Department of Energy
Thermal EmittanceThermal Emittance
22 cm
Er
e
kth
0 10 20 30 40 50 60 70 800.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.8
RF phase (degrees)
N (
mm
-mra
d)
0 0.2 0.4 0.6 0.8 1 1.20
0.2
0.4
0.6
0.8
1
1.2
Horizontal RMS laser size (mm)
N (m
m-m
rad)
Electrons are emitted with a kinetic energy Ek
laser spot assumed uniformwith radius r
RFRFRFk EhE sin
Example of measurement for Cu-cathode
AG EE or ,
(Courtesy of W. Graves)
Linear fit gives Ek=0.43 eVNonlinear fit gives rf=3.1+/-0.5, cu=4.73+/-0.04 eV, and Ek=0.40 eV
ICFA/BD Sardinia July 2002
Brookhaven Science AssociatesU.S. Department of Energy
Mg thermal EmittanceMg thermal Emittance
., constaiswhereL res
quadresres
8.2 mlinac
SolenoidRF gunQuadrupol
e
BPM
Faraday Cup
Brookhaven Science AssociatesU.S. Department of Energy
Slice Emittance
Brookhaven Science AssociatesU.S. Department of Energy
RF Photoinjector TheoryRF Photoinjector Theory
• Are all emittance uncorrelated?
K-J.’s theory:
Emittnace growth (Rieser):
scrfther222
2/1
02
0515
~1
w
UxNr
in
c
ni
nf
)(sin
11
4 0
AI
I
k xA
scnx
Brookhaven Science AssociatesU.S. Department of Energy
• 1300 MHz• Eb = 15-20 MeV• Imacro = 100-400 mA• Q = 1-4 nC• rms = 1.6 mm-mrad• = 0.2%• Injection = 30o
• Solenoid = 300A• Bucking Sol. = 310A
The Advanced FEL Photoinjector Operates at 20 MV/m Gradient and 200 mA Average Current
(D. Nguyen’s talk at BNL PERL workshop, Jan 2001)
Brookhaven Science AssociatesU.S. Department of Energy
Brookhaven Science AssociatesU.S. Department of Energy
Brookhaven Science AssociatesU.S. Department of Energy
Emittance Optimization at 45 MeV
Brookhaven Science AssociatesU.S. Department of Energy
Brookhaven Science AssociatesU.S. Department of Energy
Timing jitter effects – photocathode RF gun
Timing jitter effects – photocathode RF gun
15 20 25 30 35 40 45 50 550
1
2
3
4
5
6
RF Gun Phase (Deg.)
Ele
ctro
n b
ea
m b
unch
leng
th (
FW
HM
.ps)
40 pC
80 pC
150 pC
200 pC
Jitter smaller < 200 fs (rms)
Brookhaven Science AssociatesU.S. Department of Energy
Longitudinal Emittance Compensation
15 20 25 30 35 40 45 50 550
1
2
3
4
5
6
RF Gun Phase (Deg.)
Ele
ctro
n b
ea
m b
unch
leng
th (
FW
HM
.ps)
40 pC
80 pC
150 pC
200 pC
25 30 35 40 45 50 55 60 650.5
1
1.5
2
2.5
3
3.5
RF Gun Phase (Deg.)
No
rma
lize
d R
MS
Em
itta
nce
(m
m-m
rad
)
¬ 100 pC
¬ 300 pC
450 pC ®
•Phys. Rev. E. 54, R3121 (1996)
• PAC 97
Energy vs. initial phase for Ecathode=25.50,100Mv/m
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 50 100 150
25Mv/m
50Mv/m
100Mv/m
Brookhaven Science AssociatesU.S. Department of Energy
Linac 2000)
Brookhaven Science AssociatesU.S. Department of Energy
BuncherBuncher
head
tail
Brookhaven Science AssociatesU.S. Department of Energy
M r e c y1 p s
1 %
20 pC at 40 MeV
Presented at the linac 2000
Brookhaven Science AssociatesU.S. Department of Energy
10 fs kilo-Ampere Electron beam generation
10 fs kilo-Ampere Electron beam generation
20pc,100Mv/m,drift=3.05,12.0degree,8ps,R=0.75mm,Bf=0.70 sigma-z
0.00E+00
2.00E+02
4.00E+02
6.00E+02
8.00E+02
1.00E+03
1.20E+03
1.40E+03
0.00E+
00
1.00E+
02
2.00E+
02
3.00E+
02
4.00E+
02
5.00E+
02
6.00E+
02
7.00E+
02
8.00E+
02
5 1.5 0.0039616 1.529 0.0039047 1.57 0.0038468 1.623 0.0037879 1.687 0.003727
10 1.764 0.00366611 1.853 0.00360412 1.952 0.00354113 2.057 0.00347714 2.17 0.00341315 2.287 0.00334716 2.41 0.00328117 2.537 0.00321418 2.618 0.00317319
20pc,100Mv/m ,drift=3.05,12.0degree,8ps,R=0.75m m ,Bf=0.70 em ittance-z
0
0.5
1
1.5
2
2.5
3
3.5
4
0 50 100 150 200 250
20pc,100Mv/m ,drift=3.05,12.0degree,8ps,R=0.75m m ,Bf=0.70 em ittance-x
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0 50 100 150 200 250
20pc,100Mv/m ,drift=3.05,12.0degree,8ps,R=0.75m m ,Bf=0.70
s igm a-x
0.00E+00
2.00E-02
4.00E-02
6.00E-02
8.00E-02
1.00E-01
1.20E-01
1.40E-01
0.00E+00 2.00E+02 4.00E+02 6.00E+02 8.00E+02
20pc,100Mv/m ,drift=3.05,12.0degree,8ps,R=0.75m m ,Bf=0.70 s igm a-z
0.00E+00
2.00E+02
4.00E+02
6.00E+02
8.00E+02
1.00E+03
1.20E+03
1.40E+03
0.00E+0
0
1.00E+0
2
2.00E+0
2
3.00E+0
2
4.00E+0
2
5.00E+0
2
6.00E+0
2
7.00E+0
2
8.00E+0
2
20pc,100Mv/m,drift=3.05,12.0degree,8ps,R=0.75mm,Bf=0.70 energy
0
5
10
15
20
25
30
35
40
45
0 100 200 300 400 500 600 700 800
20pc,100Mv/m,drift=3.05,12.0degree,8ps,R=0.75mm,Bf=0.70 de/e
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0 50 100 150 200 250
10. 8 fs
Brookhaven Science AssociatesU.S. Department of Energy
0 1 2 3 4 5 6 7 80
200
400
600
800
1000
1200
1400
Distance (m)
RM
S b
un
chle
ng
th (
fs)
RMS bunch length increase from12.9 to 19.3 fs
0 1 2 3 4 5 6 7 80.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
Distance (m)
No
rma
lize
d R
MS
em
itta
nce
(m
m-m
rad
) no focusingfocusing
Charge: 50 pCrms bunchlength:19 fs
Brookhaven Science AssociatesU.S. Department of Energy
Summary of Kilo-Ampere Electron Beam Summary of Kilo-Ampere Electron Beam
20 40 60 80 100 120 140 160 180 20010
20
30
40
50
60
70
80
90
Charge(pC)
RM
S B
unch
leng
th(f
s)
20 40 60 80 100 120 140 160 180 2000.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
Charge (pC)
RM
S e
mitt
an
ce (
mm
-mra
d)
X.J. Wang and X.Y. Chang, NIMA 507 (2003) 310–313