Beyond 3rd Generation: Overview
NSF Workshop on Light Source Facilities
Lawrence Livermore National Laboratory
January 9-10, 2008
S. Krinsky
BNL
1
BROOKHAVEN SCIENCE ASSOCIATES
Fourth Generation Sources
Continuous Sources
• Storage Ring
• Energy Recovery Linac
Pulsed Sources
• Self-Amplified Spontaneous Emission
• Seeded Free-Electron Laser
2
BROOKHAVEN SCIENCE ASSOCIATES
Light Source Development
Courtesy D. Moncton
Courtesy J. Corlett
3
BROOKHAVEN SCIENCE ASSOCIATES
Fourth Generation Storage Ring
Horizontal emittance determined by equilibrium between radiation damping
and quantum fluctuation: !H~"2/MCell3
Small emittance (~30pm)! large circumference (>2km) and small
dispersion ! strong chromaticity sextupoles ! Limited dynamic aperture
& energy acceptance! short lifetime & difficult injection
One possibility is to have an accumulator ring and the storage ring and transfer
the beam periodically (few minutes) via on-axis injection
4
BROOKHAVEN SCIENCE ASSOCIATES
Energy Recovery Linac
Superconducting linac: after use the electron beam is re-circulated through
the linac at decelerating phase returning energy to the RF cavities
Emittance is determined by the normalized emittance of the electron source
! = !n / "
5
BROOKHAVEN SCIENCE ASSOCIATES
Cornell Energy Recovery Linac (ERL)
Modes
Hiflux
HiCoherence
Energy (GeV)
5
5
Current (mA)
100
25
Bunch Charge (pC)
77
19
Repetition Rate (MHz)
1300
1300
Geom. Emittance, both
Horiz. & Vert. (pm)
30
8
RMS Bunch Length (fs)
2000
2000
Relative electron energy
spread (x10-3)
0.2
0.2
Courtesy S. Gruner
6
BROOKHAVEN SCIENCE ASSOCIATES
Ph/s/0.1%/mm2/mrad2
Transverse coherent fraction
Cornell Energy Recovery Linac (ERL)
Key technical challenges
• development of low emittance, high average current electron source
• transport of the electron beam while maintaining the small emittance
• achieve level of stability now routine in storage rings
7
BROOKHAVEN SCIENCE ASSOCIATES
Undulator Radiation
$w
K2
$r "
)
(1 !
2
2
2#
%$
1
"
$r Nw
r
! coh " $2. / %$ " N w $
%$
$r
$ w +) K 2 2 2 (&
)1 !
$ r(, ) "
!# , &
))
&&
2
2
2# *
'
8
"
# 02, w 2
1! K2 / 2
,w "
"
1
2Nw
$r
Lw
BROOKHAVEN SCIENCE ASSOCIATES
Coherent Emission
Radiation
electrons
….....
n -t .
undulator
Z=Lw
Z=0
E -t .
tj : arrival time of jth electron at z=0
~
Ne
~
E -/ . " E1 -/ . 0 e
i/ t j
j "1
2
i/ t 3
6
I -/ . 8 I1 -/ . N e ! N e -N e 7 1. 9 dt n -t . e
45
12
Coherent emission
Incoherent emission
Coherent emission is important when electrons are
bunched on scale of the radiation wavelength
9
BROOKHAVEN SCIENCE ASSOCIATES
Energy Modulation of Electron Beam
At resonance, while traversing one period of the undulator, the
electron falls one radiation wavelength behind the EM-wave
1! K 2 / 2
$w " $s
2
2# r
%# " ; sin:
: =Phase of electron relative to EM-wave
%#
#
:
10
BROOKHAVEN SCIENCE ASSOCIATES
Optical Klystron
seed !
energy
modulator
%#
e-
#0
dispersion section
R56
" ; sin:
Radiator
% s " R56
out !/m
%#
#0
e-
n -: .
%#
#
:
:
11
BROOKHAVEN SCIENCE ASSOCIATES
FEL Amplifier
=
e-,aw
E
LG 8
$w
4A @
Energy Modulation
Spatial Bunching
(2 @ )3 "
J
=
2
<J
1 < =
2
) E " ?o T
(> 7
<t
c 2 <t 2
$ $w
A Area #
D#
E@
#
-K
/ 2 . BJJ C I e
1! K2 / 2 IA
2
2
Fn
$
F" ~
# 4A
Psat -GW . 8 @ I e - Amp . E -GeV .
12
BROOKHAVEN SCIENCE ASSOCIATES
electrons
….....
Tb
SASE
undulator
Z=Lw
Z=0
dPav 6+ dP (
8 4)
&
d/ 45* d/ '
seed
+ dP (
!)
&
* d/ '
Noise
31
1 e
12 9
/ 7/ r .2
7
2
2D /
e
z
LG
Single shot intensity
SASE: Single Transverse Mode, Many Longitudinal Modes
# temporal modes=Tb/Tcoh
Tcoh " A / D /
Single shot spectrum
SASE Av Spectrum
time
D/
13
BROOKHAVEN SCIENCE ASSOCIATES
Difficulty increases as output wavelength decreases
Energy (GeV)
100 nm
.3
Peak Current (Amp)
0.15 nm (LCLS)
14
500
3400
0.1 nm(XFEL)
20
5000
N. Emittance (mm-mrad)
3
1.2
1.4
Energy Spread (%)
.05
.01
.005
Undulator Length (m)
15
120
170
Pierce Parameter
2x10-3
5x10-4
14
BROOKHAVEN SCIENCE ASSOCIATES
LCLS
rf
gun
Single bunch, 1nC, 1.2#m!rad,"120"H*
L0
...existing linac
L1
X
L2
L3
undulator
Key Technical Challenges
• Photo-injector (project has achieved excellent results)
• Bunch compression and transport through maintaining
e-beam brightness
• Controlling wakefield effects
• Trajectory through long undulator
• Production of fs pulses
15
BROOKHAVEN SCIENCE ASSOCIATES
High-Gain Harmonic Generation (HGHG)
Using seed one can achieve full temporal coherence
dispersion section
modulator
seed
radiator
output
• energy modulation
• spatial bunching in
dispersion section
• coherent emission in
first part of radiator
• exponential gain in
second part of radiator
16
BROOKHAVEN SCIENCE ASSOCIATES
Spectrum of HGHG (800nm!266nm) and unsaturated SASE
under the same electron beam condition
L.H. Yu et al
BNL/
HGHG
Intensity (a.u.)
DUV-FEL
PRL 91 (2003)
0.23 nm FWHM
SASE x105
Wavelength (nm)
17
BROOKHAVEN SCIENCE ASSOCIATES
Cascaded HGHG
Use output of one HGHG stage as input to next
5"
"
25"
e-
e-
Key Technical Challenges
• Development of short wavelength seed laser
• Synchronization of lasers
• Demonstration of cascading
• Tunable output wavelength
(Shaftan & Yu have demonstrated scheme to vary output wavelength
with constant seed wavelength)
18
BROOKHAVEN SCIENCE ASSOCIATES
A Seeded X-Ray FEL User Facility
19
BROOKHAVEN SCIENCE ASSOCIATES
Performance Goals
source
ERL
LCLS
XFEL
SXFEL
# trans.
modes
1-2
1
1
1
# long.
modes
104
103
<103
1
photons/
pulse
106
1012
1012
>1011
pulses/
second
109
102
104
106
Based on table from D. Moncton
20
BROOKHAVEN SCIENCE ASSOCIATES