Post on 03-Feb-2016
description
Accelerator Laboratory of Tsinghua University
Generation, measurement and applications of high brightness electr
on beam
Dao Xiang
Apr-17, 2008
1/37
Accelerator Laboratory of Tsinghua University
X-Ray Free Eelectron Laser (XFEL)
5/ 6
1/ 2gp
LI
photoinjector
bunch compressor
2/37
Need for high brightness beam
Accelerator Laboratory of Tsinghua University
1 2
x y
n nL f
3/37
International Linear Collider (ILC)
Need for high brightness beam
Accelerator Laboratory of Tsinghua University
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)
Need for high brightness beam
Courtesy of P. Muggli , et al. Phys. Rev. Lett, 93, 014802 (2004)
Courtesy of Ian Blumenfeld , et al. Nature, 445, 741 (2007)
Accelerator Laboratory of Tsinghua University
5/37
Time-resolved femtosecond electron diffraction (FED)
Need for high brightness beam
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
Accelerator Laboratory of Tsinghua University
An atomic view of structure evolution, e.g. melting, using ultrafast electron diffraction
Courtesy of B. Siwick, et al, Science, 302, 1382 (2003)
Time-resolved femtosecond electron diffraction (FED)
Need for high brightness beam
Laser pulse
T
Al
Probe pulse
6/37
Accelerator Laboratory of Tsinghua University
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
Time-resolved femtosecond electron diffraction (FED)
Need for high brightness beam
7/37
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
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
Generation of high brightness beam
10/37
Accelerator Laboratory of Tsinghua University
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
Reduction of thermal emittance
Generation of high brightness beam
11/37
Accelerator Laboratory of Tsinghua University
sextupole
0.70 mmmrad
0.59 mmmrad
Half of the emittance is from nonlinear space charge force
Nonlinear emittance compensation
Generation of high brightness beam
12/37
Accelerator Laboratory of Tsinghua University
Recovered distribution
13/37
Computerized tomography (CT)
Accelerator Laboratory of Tsinghua University
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
Computerized tomography (CT)
quadmeasurement screen
Accelerator Laboratory of Tsinghua University
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
Computerized tomography (CT)
Accelerator Laboratory of Tsinghua University
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
Computerized tomography (CT)
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
Slit mask Magnified picture
Experimental setup
• width 80 m
• thickness 2 mm
• distance 30~40cm
• spacing 0.8~1mm
19/37
Multi-slit based emittance measurement
Accelerator Laboratory of Tsinghua University
Raw image
• Q = 200 pC
• σ= 5 ps (FWHM) = 30• E = 2.6 MeV
Comparison with simulation
Projected profile
20/37
Multi-slit based emittance measurement
Accelerator Laboratory of Tsinghua University
Q = 25 pC
Q = 100 pC
Raw image simulation experiment
22/37
Multi-slit based emittance measurement
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
Bunch length measurement Martin-Puplett interferometer
( ) ( ) ( 1) ( )b eP P N N N F
26/37
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
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)
Accelerator Laboratory of Tsinghua University
Bunch length measurement
Set up for bunch length measurement
29/37
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
Imaging of high-energy beam with ODR PSF of ODR
circular aperture semiinfinite plane rectangular slit
PSF
PSF PSF
34/37
Accelerator Laboratory of Tsinghua University
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
Accelerator Laboratory of Tsinghua University
ODR angular distribution
* 0.55 m, σ=16.7m
* 2 *( ) /s s
σ=0.6mm
Slit width: 12mmproton
LHC diagnostics with ODR
36/37
Accelerator Laboratory of Tsinghua University
Summary Applications of high brightness beam
Generation of high brightness beam
Measurement of high brightness beam
37/37
XFEL, ILC, PWFA, FED
Reduction of thermal emittance
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!