Transcript ERL Science

ERL & Coherent X-ray Applications
Qun Shen
Cornell High Energy Synchrotron Source (CHESS)
Cornell University
Talk Outline
 Introduction to x-ray coherence
 Coherent x-ray applications
 Desired ERL properties
 Options and improvements
 Conclusions
Shen 3/31/03
Source Emittance and Brilliance
x
x’
 Phase-space Emittance:
EM wave:
x’
sx’
E(r, t) = E0 ei(k·r-wt)
ex = sx sx’
sx
Integrated
total flux Fn
y’
sy’
ey = sy sy’
x
sy
E
sE
et = st sE / E
y
st
t
 Brilliance: photon flux density in phase-space
Average B =
Shen 3/31/03
Fn
(2p)2 ex ·ey
^=
Peak B
Fn
(2p)3 ex ·ey·et
Spatial (Transverse) Coherence
2s
2s

Dl =   2s = l/2
2s'
=>
2  2s ~ l
  s'
=> X-ray beam is spatially coherent
if phase-space area 2ps’s < l/2
Diffraction limited source: 2ps's = l/2 or e = l/4p
Almost diffraction limited: 2ps's ~ l or e ~ l/2p
Shen 3/31/03
Temporal (Longitudinal) Coherence
l
l+Dl
Coherence length: lc = l2/Dl
Coherence time: Dtc = lc/c
lc = l2/Dl
Temporally coherent source:
pulse length FWHM t  Dtc
For l = 1 Å, Dl/l = 10-4 :
lc = 1 mm, Dtc = 1 mm / 3x108 m/s = 3.3 fs
 uncertainty: t ·Dn  1
t ·DE  h
Degeneracy Parameter dD
X-ray optics can modify Dl/l, but extinction length
(~100mm) limits to Dl/l = 10-6 => Dtc= 330 fs
= Number of photons in
coherent volume
 ERL with st = 100 fs pulses coupled with 10 meV
x-ray monochromator could mean temporal
coherence at 10 keV.
= Number of photons within
single quantum mode
Shen 3/31/03
Transverse Coherence from Undulator
d

L
 = l/2d
Example: APS, L =2.4m, l =1.5Å
  2.35 s r2' +s ' 2
sr' = 13.1 mrad
s r' 
dy = 2.35x21mm, sy' = 6.9 mrad
 = 1.5 mrad,  = 2.35x14.8 mrad
=> pc(vertical) = 4.3%
dx = 2.35x350mm, sx' = 23.1 mrad
 = 0.091 mrad,  = 2.35x26.6 mrad
=> pc(horizontal) = 0.15%
Shen 3/31/03
2L
 A portion, / in each direction,
of undulator radiation is spatially
coherent within central cone
 Coherent fraction pc: depends
only on total emittances
=> pc (overall) = 0.006%
ERL: pc ~ 20% (45% in x or y)
l
pc 
Fc ( l /2 ) 2 B
l2


Fn
Fn
( 4p ) 2 e x e y
ERL Spatial Coherence
Diffraction limited @ 8keV (0.123Å)
ESRF emittance
(4nm x 0.01nm)
ERL emittance (0.015nm=0.15Å)
Diffraction limited source: 2ps's = l/2 or e = l/4p
Almost diffraction limited: 2ps's ~ l or e ~ l/2p
Phase II ERL: diffraction-limited source E < 6.6 keV
almost diffraction-limited to 13 keV
Shen 3/31/03
X-ray Coherence Workshop Program
http://www.chess.cornell.edu/Meetings
Friday, 22 August, 2003
8:30
Qun Shen (CHESS)
Welcome
8:35
Sol Gruner (Cornell)
Energy recovery linac source properties
8:55
Jerry Hastings (SLAC)
XFEL source properties
9:15
Bruno Lengeler (Aachen)
Tutorial on X-ray coherence
10:05
Coffee Break
10:30
Mark Sutton (McGill)
X-ray photon correlation spectroscopy
8:30
Chris Jacobsen (SUNY-SB) Overview on coherent x-ray microscopy
11:00
Gerhard Gruebel (ESRF)
Coherent SAXS
9:00
Keith Nugent (Melbourne)
Phase imaging and phase retrieval
11:30
Jeroen Goedkoop (WZI)
Magnetic speckle
9:30
Peter Cloetens (ESRF)
3D phase tomography
Discussion on coherent scattering I: time
correlation
10:00
12:00
Saturday, 23 August, 2003
10:15
Coffee Break
10:35
Enzo Di Fabrizio (Eletra)
Wavefront shaping & lithography
11:05
Anatoly Snigirev (ESRF)
Fourier transform holography
Makina Yabashi (SPring8)
Two-photon interferometry
12:15
Lunch
14:00
Ian Robinson (UIUC)
14:30
John Spence (ASU)
15:00
Coffee Break
15:20
Tetsuya Ishikawa (SPring8)
15:50
Christian David (PSI)
Coherence preserving reflecting and crystal optics
Diffractive optics and shearing interferometer 14:00
16:20
David Paterson (APS)
X-ray coherence measurements
Discussion on coherent optics
16:50
Crytallography on nanocrystallites
11:35
Ptychography and diffractive imaging: How it
12:05
works, with electrons and x-rays
12:20
Discussion on holography and interferometry
Lunch
David Sayre (SUNY-SB)
Crystallography applied to noncrystalline materials
14:30
John Miao (SSRL, SLAC)
Imaging with single molecule diffraction
15:00
Malcolm Howells (LBNL)
Holography by phase retrieval
15:30
Shen 3/31/03
Discussion on phase contrast microscopy
Discussion on coherent scattering II: structure
determination
X-ray Microscopy
ESRF ID21: TXM 3-6 keV
ESRF ID21: SXM 2-10 keV & < 2keV
 transmission
 fluorescence
 XPEEM
ERL hi-coherence
 Two types: full field & scanning
 All types of materials are studied, from biological
to magnetic
 Increasing number of SR imaging microscopes
worldwide due to availability of
=> lens-like optics: zone plates, KB mirrors, CRLs
=> high-brilliance & high-energy synchrotron sources
Shen 3/31/03
Issues in Hard X-ray Microscopy
 Phase contrast is x104 higher than absorption
contrast for protein in water @ 8keV
 Focusing optics
Only recently has Fresnel zone-plate (FZP)
achieved <100nm resolution at 8keV (Yun, 1999)
 Dose reduced to level comparable to using
water-window in soft x-ray region
 High coherence sources:
Kirz (1995): 0.05mm protein in 10mm thick ice
l2/(exey).
Coherence fraction ~
=> Requires 100x smaller emittance product for
1keV => 10 keV
phase contrast
104
102
Refraction index: n = 1 - d - ib
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108
absorption
contrast
106
 Absorption vs. phase contrast
absorption contrast: mz = 4pbz/l ~ l3
phase contrast: f(z) = 2pdz/l ~ l
1010
Dose (Gr)
ERL would offer 102-103x better emittance
product than present-day hard x-ray sources
=> Better coherence @10 keV than @1 keV at ALS
C94H139N24O31S
z
103
104
X-ray Energy (eV)
 In general, phase contrast requires:
=> coherent hard x-ray beams
Phase Imaging & Tomography
l
Cloetens et al. (1999): ESRF, ID19, 18 keV
Polystyrene foam 0.7x0.5x1mm3
1.4T wiggler, B~7x1014 ph/s/mr2/mm2/0.1% @100mA
4x700 images at 25 sec/image
 A form of Gabor in-line holography
 Coherence over 1st Fresnel zone (lR)1/2
 Image reconstruction (phase retrieval)
 Spatial resolution limited by pixel size
• With ERL: it would be possible to reduce
the exposure times by orders of magnitude.
• It offers great potential for flash imaging
studies of biological specimens, at ID beam
lines.
Shen 3/31/03
Far-Field Diffraction Microscopy
 Diffraction microscopy is analogous to crystallography,
but for noncrystalline materials
 Coherent diffraction from noncrystalline specimen:
=> continuous Fourier transform
 Spatial resolution: essentially no limit.
(only limited by Dl/l and weak signals at large angles)
 Coherence requirement: coherent illumination of sample
Coherent X-rays
 Key development: oversampling phasing method
coherent flux!!
Miao et al. (1999) >>>
soft x-rays, reconstruction
to 75 nm
Shen 3/31/03
Diffraction Microscopy
recent results
Miao et al. PRL (2002)
l=2Å
reconstructed image:
to d~7nm resolution
Gold: 2.5mm x 2mm x 0.1mm
SPring-8 BL29XU:
standard undulator 140 periods lu=3.2 cm
B=2x1019 ph/s/mr2/mm2/0.1% @100mA
For Au, exposure time 50 min, d~7nm
but: for Si, (ZSi/ZAu)2~1/32 => 26 hrs !
for C, (Zc/ZAu)2~1/173 => 6 days !!
Shen 3/31/03
ERL high-coherence option:
B=5x1022 ph/s/mr2/mm2/0.1% @10mA
Exposure time for Si & d~7nm: 0.6 min.
for C & d~7nm: 3.5 min.
=> could achieve higher resolution,
limited only by radiation damage
Imaging Whole Escherichia Coli Bacteria
Using Single Particle X-ray Diffraction
Jianwei Miao*†, Keith O. Hodgson*‡, Tetsuya Ishikawa§,
Carolyn A. Larabell¶?, Mark A. LeGros**, and Yoshinori Nishino§
Miao et al., Proc. Nat. Acad. Sci. (2003)
E. Coli bacteria ~ 0.5 mm by 2 mm
SPring-8, l = 2 Å, pinhole 20 mm
Total dose to specimen ~ 8x106 Gray
Diffraction image to ~30nm resolution
Shen 3/31/03
X-ray Photon Correlation Spectroscopy
Dierker (2000), ERL Workshop
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X-ray Holography with Reference Wave
Leitenberger & Snigirev (2001)
Wilhein et al. (2001).
Howells et al. (2001); Szoke (2001).
Illumination of two objects, one
as reference, e.g. pin-hole arrays
• X-ray holography is exciting
but not ready for applications
• ERL is an ideal source for
further research in this area
Shen 3/31/03
Coherent X-ray Patterning & Lithography
SHAPING X-RAYS BY DIFFRACTIVE CODED
NANO-OPTICS (invited talk X-ray Coherence 2003)
Maskless pattern
Enzo Di Fabrizio
TASC-NNL-INFM (National Institute for the Physics of Matter) Elettra Synchrotron Light Source
DOE: diffractive
optics element
Lithography 
X-ray CVD 
Coherent X-rays
Shen 3/31/03
Desired ERL Properties
X-ray photon correlation spectroscopy
Phase-contrast imaging & microscopy
Coherent far-field diffraction
Coherent crystallography
X-ray holography
Coherent x-ray lithography
full transverse coherence
high coherent flux / coh. fraction
high Dl/l for high resolution
small beam (some cases)
large coherent area (some cases)
CW operation: long pulses okay
Basic Requirement:
 low transverse emittances
D1
D2
 X-ray optical slope error
d << sx/D1 ~ 4mm/40m ~ 0.1mrad
Shen 3/31/03
 long undulators (large Nu)
 low machine energy spread
 coherence preserving x-ray optics
Coherent Flux (photons/s/0.1%)
Phase II ERL Coherent Flux
10
15
10
14
LCLS SASE
ERL 25m
0.015nm 10mA
APS 4.8m
10
13
10
12
10
11
10
10
 Coherent fraction ~100x
greater than 3rd SR sources
Sp8 25m
ESRF U35
Sp8 5m
10
 Peak coherent flux (coherent
flux per pulse) ~1000x greater
than 3rd SR sources
APS 2.4m
???
9
3
4
5 6 7 8 910
20
Photon Energy (keV)
Shen 3/31/03
 Time-averaged coherent flux
comparable to LCLS XFEL
0.15nm 100mA
30
40 50
CHESS Tech Memo 01-002: 3/8/01
http://erl.chess.cornell.edu/papers
Assuming high duty-cycle ERL
ERL
APS
APS
ESRF Spring8 Spring8 LCLS
operations
hi-flux hi-coh. und. A upgrade U35
5m
25m spont.
Machine design
Energy EG (GeV)
5.3
5.3
7
7
6
8
8
Insertion
device
DC experiments
Pulsed expts.
15
-6
72· 10 72· 10
-6
25
25
0.063
0.063
Current I (mA)
100
10
100
300
200
100
100
Charge q (nC/bunch)
0.077
0.008
14
14
0.85
0.29
0.29
1
1
1
1
ex (nm-rad)
0.15
0.015
8
3.5
4
6
6
0.05
0.05
0.02
0.02
ey (nm-rad)
0.15
0.015
0.08
0.0035
0.01
0.003
0.003
0.05
0.05
0.02
0.02
Bunch fwhm t (ps)
0.3
0.3
73
73
35
36
36
0.23
0.23
0.188
0.090
120
120
56575
56575
# of bunches f (Hz) 1.3· 109 1.3· 109 7.3· 106 22· 106 2.3· 108 3.4· 108 3.4· 108
Undulator L (m)
25
25
2.4
4.8
5
4.5
25
100
100
30
87
Period lu (cm)
1.7
1.7
3.3
3.3
3.5
2.4
3.2
3
3
3.81
5
# of period Nu
1470
1470
72
145
142
187
781
3300
3300
787
1740
Ave. flux Fn (p/s/0.1%) 1.5· 10161.5· 10157.0· 10144.2· 10151.3· 10152.4· 10159.0· 10153.3· 10102.4· 10146.4· 1012 4· 1017
Ave. brilliance B
22
22
19
21
20
20
21
17
22
19
25
(p/s/0.1%/mm2/mr2) 1.3· 10 5.2· 10 1.5· 10 1.5· 10 3.1· 10 5.0· 10 2.2· 10 1.6· 10 4.2· 10 3.6· 10 8· 10
Coh flux Fc (p/s/0.1%) 8.1· 10133.1· 10140.9· 10119.0· 10121.8· 10123.0· 10121.3· 1013 9.0· 108 2.4· 10141.4· 1011 4· 1017
Coh. fraction pc (%)
Photons / bunch
Peak brilliance
(p/s/0.1%/mm2/mr2)
0.52
20
0.013
0.22
0.14
0.13
0.14
2.7
100
2.1
100
1.2· 107 1.2· 106 9.6· 107 1.9· 108 5.7· 106 7.1· 106 2.7· 107 2.8· 108 2· 1012 1.1· 108 7· 1012
3.0· 10251.2· 10262.5· 10228.3· 10233.3· 10223.6· 10221.6· 10234.8· 10271.2· 10333.4· 1027 7· 1033
Peak flux (p/s/0.1%) 3.9· 10193.9· 10181.3· 10182.6· 10181.6· 10171.9· 10177.4· 10171.2· 10217.2· 10246.0· 1020 3· 1025
Pk coh. flux (p/s/0.1%) 2.1· 10177.9· 10171.7· 10145.6· 10152.2· 10142.5· 10141.1· 10152.7· 10197.2· 10241.4· 1019 3· 1025
Peak degen. par. dD
Shen 3/31/03
15
LCLS TESLA TESLA
SASE spont. SASE
95
368
0.078
2.6
0.103
0.113
0.49
1.3· 104 3.3· 109 4.7· 103 8· 109
Desired Changes to Memo
 Performance numbers for micro-beam undulator
 Separate ultra-fast mode: less frequent fat bunch q
 Inclusion of effects of machine energy spread sE
transverse exey
scale with q
1.0
E1[keV] 
Relative Flux Gain
0.8
Relative Gain in Undulator Flux

  22.35s E

DE1
1

E1
N0
0.4
Decrease due to
Energy Spread sE
0.2
0
1
2
3
Undulator Length Nu / N0
Shen 3/31/03
(1 + K 2 / 2) lu [cm ]
 DEG
DE1
 2 
E1
 EG
0.6
0.0
0.95  EG2 [GeV ]
4
5
DE
1

E
Nu
Phase II ERL Properties
Type of experiments
Machine energy
Charge per bunch
Repetition rate
Machine current
Horizontal emittance
Vertical emittance
Rms bunch length
Energy spread
Limit on number of periods
Diffraction-limited to
Undulator length
Undulator period
Number of periods
Effective number of periods
Horizontal beta
Vertical
Averagebeta
flux
Deflection
Averageparameter
brilliance
Magnetic
Average flux density
@field
1:1
Peak
flux
Fundamental
energy
Peak
brilliance
Fundamental
wavelength
PhotonsParameter
per pulse
Coherent
flux
Parameter
Total source size x
Total source divergence x
Total source size y
Total source divergence y
Shen 3/31/03
E (GeV)
q (nC)
f (MHz)
I (mA)
e x (nm-rad)
e y (nm-rad)
st (ps)
sE /E
N0
Ed (keV)
L (m)
lu (cm)
Nu
Neff
b x (m)
b ny (m)
F
(p/s/0.1%)
Kn (std units)
B
B (T)
(p/s/0.1%/mm2)
F
Ep1 (p/s/0.1%)
(keV)
B
(std units)
l1p (A)
n
p (p/0.1%)
K2/4/(1+K2/2)
F
Qcn (p/s/0.1%)
(n=1)
sx (mm)
sx' (mrad)
sy (mm)
sy' (mrad)
Hi-flux
Hi-coh I
Hi-coh II
m-beam
5.3
0.077
1300
100
0.15
0.15
2.0
0.0002
1064
0.658
25
1.7
1470
861.8
12.5
12.5
8.81E+15
1.34
7.74E+21
0.84
7.30E+11
1.27E+18
8.27
1.11E+24
1.50
6.78E+06
0.2365
4.35E+13
0.7139
43.85
3.87
43.85
3.87
5.3
0.0077
1300
10
0.015
0.015
2.0
0.0002
1064
6.578
25
1.7
1470
861.8
4.0
4.0
8.81E+14
1.34
3.08E+22
0.84
1.31E+12
1.27E+17
8.27
4.43E+24
1.50
6.78E+05
0.2365
1.73E+14
0.7139
10.35
2.60
10.35
2.60
5.3
0.0077
1300
10
0.015
0.015
2.0
0.0002
1064
6.578
30
1.5
2000
939.2
4.8
4.8
1.04E+15
1.52
3.63E+22
1.08
1.29E+12
7.49E+16
8.25
2.61E+24
1.50
8.00E+05
0.2680
2.05E+14
0.7733
11.34
2.38
11.34
2.38
5.3
0.0077
1300
10
0.015
0.015
2.0
0.0002
1064
6.578
3.4
1.4
240
234.1
0.5
0.5
2.67E+14
1.6
9.40E+21
1.22
2.96E+12
3.84E+16
8.36
1.35E+24
1.48
2.05E+05
0.2807
5.17E+13
0.7949
3.79
7.08
3.79
7.08
Ultra fast I Ultra fast II
5.3
0.4
0.01
0.004
0.108
0.108
0.1
0.0027
79
0.913
2.2
1.4
160
70.7
1.0
1.0
3.46E+10
1.9
5.20E+16
1.45
4.87E+07
1.30E+19
6.80
1.95E+25
1.82
3.46E+06
0.3217
4.33E+08
0.8559
10.64
12.20
10.64
12.20
5.3
1.2
0.01
0.012
0.187
0.187
0.1
0.0027
79
0.527
2.2
1.4
160
70.7
1.0
1.0
1.04E+11
1.9
6.00E+16
1.45
8.59E+07
3.89E+19
6.80
2.25E+25
1.82
1.04E+07
0.3217
4.99E+08
0.8559
13.87
15.10
13.87
15.10
Options for Improvements
 Injector emittance ?
0.015 nm-rad  ??
 Separate running modes for hi-coherence & ultra-fast ?
 Bunch decompression  longer pulse but smaller sE/g ??
on-crest
Df  0
Shen 3/31/03
No Compression
st ~ 2 ps
sE/g ~ 2x10-4
off-crest
Df > 0
st ~ 0.1 ps
sE/g ~ 2.7x10-3
off-crest
Df < 0
st ~ ?? ps
sE/g ~ 1x10-4 ?
Improved Coherence Properties
by reducing machine energy spread
Operation Mode:
Type of experiments
Machine energy
Charge per bunch
Repetition rate
Machine current
Horizontal emittance
Vertical emittance
Rms bunch length
Energy spread
Limit on number of periods
Diffraction-limited to
Undulator length
Undulator period
Number of periods
Effective number of periods
Average brilliance
Average flux density @ 1:1
Peak flux
Peak brilliance
Coherent flux
Shen 3/31/03
E (GeV)
q (nC)
f (MHz)
I (mA)
e x (nm-rad)
e y (nm-rad)
st (ps)
sE /E
N0
Ed (keV)
L (m)
lu (cm)
Nu
Neff
Bn (std units)
(p/s/0.1%/mm2)
Fp (p/s/0.1%)
Bp (std units)
Fc (p/s/0.1%)
on-crest
Df=0
Hi-flux
5.3
0.077
1300
100
0.15
0.15
2.0
0.0002
1064
0.658
25
1.7
1470
861.8
7.74E+21
7.30E+11
1.27E+18
1.11E+24
4.35E+13
off-crest
Df<0 ?
Hi-coh I
Hi-coh II
m-beam
5.3
0.0077
1300
10
0.015
0.015
2.0
0.0002
1064
6.578
25
1.7
1470
861.8
3.08E+22
1.31E+12
1.27E+17
4.43E+24
1.73E+14
5.3
0.0077
1300
10
0.015
0.015
4.0
0.0001
2128
6.578
25
1.7
1470
1209.4
4.32E+22
1.84E+12
8.91E+16
3.11E+24
2.43E+14
5.3
0.0077
1300
10
0.015
0.015
2.0
0.0002
1064
6.578
3.4
1.4
240
234.1
9.40E+21
2.96E+12
3.84E+16
1.35E+24
5.17E+13
off-crest
Df>0
Ultra fast I Ultra fast II
5.3
0.4
0.01
0.004
0.108
0.108
0.1
0.0027
79
0.913
2.2
1.4
160
70.7
5.20E+16
4.87E+07
1.30E+19
1.95E+25
4.33E+08
5.3
1.2
0.01
0.012
0.187
0.187
0.1
0.0027
79
0.527
2.2
1.4
160
70.7
6.00E+16
8.59E+07
3.89E+19
2.25E+25
4.99E+08
Other Properties
Type of experiments
Machine energy
Charge per bunch
Repetition rate
Machine current
Horizontal emittance
Vertical emittance
Rms bunch length
Energy spread
Bandpass for pink beam
Coherent flux in pink beam
Average flux in pink beam
Peak flux in pink beam
Photons per pulse in pink beam
Coherent flux fraction
Coherent DW fraction in ctr cone
Coherence width fwhm @100m
Coherence length for pink beam
Photons per coherent volume
Average total power
On-axis power density @20m
Peak total power
Peak electric field @ exit
Shen 3/31/03
E (GeV)
q (nC)
f (MHz)
I (mA)
e x (nm-rad)
e y (nm-rad)
st (ps)
sE /E
Dl/l (%)
Fc (p/s)
Fn (p/s)
Fp (p/s)
np (photons)
pc (%)
pc (%)
wc (mm)
lc (mm)
dD
P0 (W)
dP/dA (W/mm2)
Pp (MW)
E0 (V/m)
Hi-flux
Hi-coh I
Hi-coh II
m-beam
Ultra fast I Ultra fast II
5.3
0.077
1300
100
0.15
0.15
2.0
0.0002
5.3
0.0077
1300
10
0.015
0.015
2.0
0.0002
5.3
0.0077
1300
10
0.015
0.015
4.0
0.0001
5.3
0.0077
1300
10
0.015
0.015
2.0
0.0002
5.3
0.4
0.01
0.004
0.108
0.108
0.1
0.0027
5.3
1.2
0.01
0.012
0.187
0.187
0.1
0.0027
0.116
5.05E+13
1.02E+16
1.47E+18
7.87E+06
0.116
2.01E+14
1.02E+15
1.47E+17
7.87E+05
0.083
2.01E+14
1.02E+15
7.36E+16
7.87E+05
0.427
2.21E+14
1.14E+15
1.64E+17
8.76E+05
1.415
6.12E+09
4.90E+11
1.83E+20
4.90E+07
1.415
7.06E+09
1.47E+12
5.50E+20
1.47E+08
0.49
0.56
0.074
0.129
3
19.62
22.32
0.413
0.129
12
19.62
22.32
0.413
0.181
9
19.39
22.06
1.114
0.035
4
1.25
1.42
0.373
0.013
99
0.48
0.55
0.284
0.013
114
31,679
3,168
3,168
895
0.336
1.009
2655
266
266
62.9
0.0199
0.0597
4.563
0.456
0.228
0.129
126.0
377.9
5.34E+08 7.15E+08 5.06E+08 1.04E+09 1.16E+10 1.54E+10
Short-Pulse Source Comparison
fat bunch
Shen 3/31/03
Conclusions
 Phase II ERL would offer 100x more coherent flux and
coherence fraction for hard x-rays than present-day
sources, comparable to prototype XFEL source
 Many scientific applications benefit substantially, e.g. in
coherent scattering & diffraction, and in x-ray holography and
coherent patterning, possibly opening up new research areas
 Improvements in ERL coherent flux require long undulator,
which in turn requires reducing machine energy spread by
bunch decompression or by some other means
 Further improvements in coherence are possible only if
injector emittance can be further reduced
 Ultra-fast mode of ERL can still be a leader in peak brilliance
for short-pulses. Further improvement is determined by how
much charge in a single bunch and by energy spread from
bunch compressor
Shen 3/31/03