generation, measurement and applications of high brightness electron beam dao xiang apr-17, 2008

Accelerator Laboratory of Tsinghua University

Generation, measurement and applications of high brightness electr

on beam

Dao Xiang

Apr-17, 2008

1/37


X-Ray Free Eelectron Laser (XFEL)

5/ 6

1/ 2gp

LI

photoinjector

bunch compressor

2/37

Need for high brightness beam


1 2

x y

n nL f

3/37

International Linear Collider (ILC)



SLAC 2004 σ =2.3 ps E=200MV/m

SLAC 2006 σ =40 fs E=52GV/m

2/E N

4/37

Plasma wake-field accelerator (PWFA)


Courtesy of P. Muggli , et al. Phys. Rev. Lett, 93, 014802 (2004)

Courtesy of Ian Blumenfeld , et al. Nature, 445, 741 (2007)


5/37

Time-resolved femtosecond electron diffraction (FED)


Laser excitation pulse

∆t

sample

• Ultrafast laser pulse “pumps” a process in the sample

• Ultrafast e/n/x-ray pulse “probes” the sample after time ∆t

X-rayXFEL

neutronSNS

electronFED

Typical pump-probe scheme

Probe pulse


An atomic view of structure evolution, e.g. melting, using ultrafast electron diffraction

Courtesy of B. Siwick, et al, Science, 302, 1382 (2003)



Laser pulse

T

Al

Probe pulse

6/37


Existed facility

• Beam energy: 30~50 KeV

• Temporal resolution: ~1 ps

• Electron number per pulse: <10 k

Proposed facility

• Beam energy: 2~5 MeV

• Temporal resolution: ~100 fs

• Electron number per pulse: >106 k



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Time-resolved femtosecond electron diffraction (FED) Bragg angle ~ beam divergence

Courtesy of J.B. Hastings, et al. Appl. Phys. Lett, 89, 184109 (2006)

0.05 mrad 0.10 mrad 0.20 mrad 0.30 mrad

Courtesy of P. Musumeci, et al. Proceedings of PAC07, (2007)

8/37


Invention of photocathode rf gun

Emittance compensation

Next step

Reduction of thermal emittance

Reduction of emittance caused by nonlinear space charge force

9/37

High gradient

Beam shape control

Generation of high brightness beam


Reduction of thermal emittance Classical description of photoemission

Schottky effect: E

Quantum efficiency increase for p-polarized laser

p

s

Q vs polarization angle

polarization Reflectivity

s 0.68

p 0.23

2 2( ) ( ) kj h h E

Work function idFda


10/37


0 exp( )fi SGGf i f i

iA i AM V iG r f e G i f A V i i f i

E E E E z

p-polarized laser only!

Time-of-flight spectrometer



11/37


sextupole

0.70 mmmrad

0.59 mmmrad

Half of the emittance is from nonlinear space charge force

Nonlinear emittance compensation


12/37


Recovered distribution

13/37

Computerized tomography (CT)


14/37

011 12

021 22 ''

xR Rx

xR Rx

2 2

11 12

11 12 2 2 2 211 12 21 22

21 222 2 2 2

11 12 11 12

0cos sin

( )( ) 1 1 sin cos

R RR R

SRR R R RR RR R R R

12 11tan /R R


quadmeasurement screen


15/37

011 12

021 22 ''

xR Rx

xR Rx

I =74 A I =78 A I =82 A I =86 A

Experiment setup

0

0

0

0

1cos sin 0 0

sin cos 0 0

10 0 cos sin

0 0 sin cos

Q

QR

Q

Q

0 0 / 2Q qB mv 0Q L



16/37

residual phase space

1/ 22

2

1 1

1 1N N

x i ii i

x xN N

1/ 22

2

1 1

1 1' ' '

N N

x i ii i

x xN N

' ( )( ' ' )x x x x x x

2 2 2' ' 0.68x x x x

2

'' ' x x

x

x x x

mmmrad

Reconstructed phase space I=76A I=82A



Measurement of high brightness beam5/ 6 1/ 2/g pL I

1 2 / x yL fn n

2/E N

XFEL emittance & bunch length

ILC emittance & beam size

PWFA bunch length

emittance measurement for low energy beam

bunch length measurement for moderate energy beam

beam size measurement for high energy beam

17/37


Multi-slit based emittance measurement

2

2 3 3'' 0

( )n

xx A x y

I

I

Envelope equation

2

22x

scA n

IR

I

I=40A

σ=1mm

E=3.5 MeV

n=3mmmrad

Multi-slit based emittance measurementemittance and beam size evolution

18/37

space charge dominatedemittance dominated


Slit mask Magnified picture

Experimental setup

• width 80 m

• thickness 2 mm

• distance 30~40cm

• spacing 0.8~1mm

19/37



Raw image

• Q = 200 pC

• σ= 5 ps (FWHM) = 30• E = 2.6 MeV

Comparison with simulation

Projected profile

20/37



Q = 25 pC

Q = 100 pC

Raw image simulation experiment

22/37



Measurement of high brightness beam Bunch length measurement

Time domain methods

Frequency domain methods

diffraction radiation

deflecting cavity

streak camera

electron

metallic plate

radiation

22/37


Theory for bunch length measurement in frequency domain

Random walk model

A BC

2 /B z *

0 01 1

( ) jk

N Nii

bk j

P const E E e e

1 1

( ) jk

N Nii

ek j

P e e

2

( / )( ) ( ) i c zF S z e dz

31 2

1

...k

Ni ii i

k

e e e e

E N2P N

E N

P N

( ) ( ) ( 1) ( )b eP P N N N F

coherent radiation incoherent radiation

interferometer

calculationphase retrieval

23/37

12 3


Bunch length measurement Virtual photon

( ) ( ) ( 1) ( )b eP P N N N F

10

2( , ) (0, , ) i t

r r

e rE r E r t e dt K

c

2 / 21 12

0

2( , , ) / ( sin )

ikR b ikr Rr DR a

eeE z r rK kr J k r e dr

c R

r

z-ct

electron

observer

Virtual photon

– finite target– near field

3/ 22 2 20

( , , )4 ( )

r

e rE z r t

r z ct

E-field

Virtual photon diffraction model

Virtual photon

observer

24/37


Bunch length measurement Virtual photon diffraction model

b

R

R/2<1

Coutesy of A. G. Shkvarunets, et al, Phys. Rev. ST-AB, 11,012801 (2008)

b/<1

( ) ( ) ( 1) ( )b eP P N N N F

25/37


Bunch length measurement Martin-Puplett interferometer

( ) ( ) ( 1) ( )b eP P N N N F

26/37


Bunch length measurement Phase retrieval ( ) ( ) ( 1) ( )b eP P N N N F

2( / )( ) ( ) i c zF S z e dz Kramers-Kronig relation

2 20

ln ( )2( )

F xP dx

x

0

1'( ) ( ) cos ( ) /S z d F z c

c

Gaussian Bi-gaussian Uniform

27/37


Bunch length measurement

Experiment setup

Signal vs B-field

BC optimization

Signal vs gun phase

28/37

Signal vs linac phase

Coutesy of R. Akre, et al, Phys. Rev. ST-AB, 11,030703 (2008)


Bunch length measurement

Set up for bunch length measurement

29/37


Bunch length measurement experimental results

autocorrelation curve

束团辐射谱Before BC

After BC

bunch spectrum single electron spectrum form factor

( ) ( ) ( 1) ( )b eP P N N N F

phase space σ= 0.73 ps

31/38


Non-intercepting beam size measurement Using ODR angular distribution to measure beam size

Coutesy of P. Karataev et al, Phys. Rev. Lett, 93,244802 (2004)

30/37


2 2 2 2

, ,exp exp exp2 2l l s s

ikalL sl l l s l s s s

x y s s x y

x y x x y y x yieE ik dx dy E ik ik

a a a a

2 2, 12 2

,( )

s s

s s sx y s s

s s

x yeE K x y

v x y

2 2 2 2

, ,exp exp exp2 2i i l l

ikbi lRi i i l i l l lx y l l x y

x y x x y y x yieE ik dx dy E ik ik

b b b b

2 2, , exp / 2

l l l l

lR lLx y x y l lE E ik x y f

Virtual photo

Fresnel integration

Fresnel integration

Phase delay

Imaging of high-energy beam with ODR point spread function (PSF)

32/37


Imaging of high-energy beam with OTR big beam

Beam size 30m

Image size 30.7m

Image and beam’s real distribution for a big beam

Image of a 1m beam restored distribution

small beam PSF

33/37


Imaging of high-energy beam with ODR PSF of ODR

circular aperture semiinfinite plane rectangular slit

PSF

PSF PSF

34/37


ODR imaging as an alternative to cavity BPM

Imaging of high-energy beam with ODR

Measure beam profile

ratio vs offset

ODR beam image

Center pass

35/37


ODR angular distribution

* 0.55 m, σ=16.7m

* 2 *( ) /s s

σ=0.6mm

Slit width: 12mmproton

LHC diagnostics with ODR

36/37


Summary Applications of high brightness beam


Measurement of high brightness beam

37/37

XFEL, ILC, PWFA, FED


Nonlinear emittance compensation

Emittance measurement for low energy beam

Bunch length measurement for moderate energy beam

Beam size measurement for high energy beam

Phase space mapping with CT technique

Thanks!

generation, measurement and applications of high brightness electron beam dao xiang apr-17, 2008

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