Brookhaven Science Associates U.S. Department of Energy A Few Comments on the Photoinjector...

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