ICFA Workshop on Future Light Sources
March 5th-9th, 2012
Thomas Jefferson National Accelerator Facility
Newport News, VA
Brief Introduction to (VUV/)Soft X-ray FELs
R. P. Walker
Diamond Light Source, UK
Status of VUV/Soft X-ray FELs
Working definition:
VUV:
Soft X-ray:
~200 nm – ~20 nm (5 eV – 50 eV)
~20 nm – ~1 nm (50 eV – 1 keV)
Operating
• FLASH (Germany)
- so far the only operating soft X-ray User facility
• FERMI@ELETTRA (Italy)
- call for proposals issued; 1st external users later this year
Planned
•
•
•
•
NGLS (US): 0.28 – 1.2 keV
WiFEL (US): 5 – 900 eV
SPARX-FEL (Italy) : 30 eV – 2 keV
JLAB VUV FEL (JLAMP) (US): 600 MeV cw recirculating linac, oscillator
FEL 10-100 eV
Note that X-ray FEL facilities may also operate in the
soft X-ray range, or contain specific soft-X-ray FELs
e.g.
•
LCLS: has operated down to 400 eV
•
European XFEL SASE3: 4.7 nm – 0.4 nm (260 eV to 3 keV)
•
SwissFEL “Athos” at 2.4/3.1 GeV: 7 – 0.7 nm, variable
polarization, HHG seeding + single-stage HGHG (or other
scheme)
•
PAL-XFEL SXFEL1 at 3 GeV: 1-10 nm
Many (X)FEL test facilities are in the soft X-ray range
Operating
• SCSS (Japan): 250 MeV
• SPARC (Italy): 200 MeV
• Shanghai Deep-UV FEL (SDUV): 150 MeV
Construction
• Shanghai Soft X-ray FEL (SXFEL)
approved in Feb. 2011; construction started early 2012
840 MeV normal conducting S-band + C-band linac
possible future upgrade to 1.3 GeV for soft X-ray user facility
Planned
• CLARA (UK)
• LUNEX5 (France)
See separate session on test
facilities
Not to mention several projects that have
“fallen by the wayside ..”
•
•
•
•
•
4GLS
BESSY FEL
LUX
Arc-en-ciel
NLS … technically not dead, just not proceeding at the moment ..
Fallen by the Wayside,
E.Bundy, 1886.
FLASH Radiation Parameters 2011
Wavelength range (fundamental)
Average single pulse energy
Pulse duration (FWHM)
Peak power
Average power (example for 3000 pulses/sec)
Spectral width (FWHM)
Average Brilliance
Peak Brilliance
4.1 – 45 nm
10 – 400 μJ
50 – 200 fs
1 – 3 GW
~ 300 mW
~ 0.7 - 2 %
1017 – 1021 *
1029 – 1031 *
* photons/s/mrad2/mm2/0.1%bw
•
> 150 publications on photon science, many in high impact
journals
•
3740 hours of SASE delivery Sep. 2010 – Sep. 2011
•
Accelerator up-time ~ 96%
•
SASE delivery to experiments ~ 75% (rest is tuning, set-up etc.)
FLASH-II
•
Construction has started
•
Commissioning May 2013
•
SASE: 4-60 nm
•
HHG seeded: 10-40 nm (at 100 kHz)
FERMI@Elettra
S-band linac 1.2 GeV (later 1.5 GeV)
FEL-1: HGHG down to 10nm
Status: operating 20-65 nm
FEL2: two stage HGHG with fresh bunch technique, to 4 nm (1.5 GeV)
Status: install & commission in 2012
FERMI@ELETTRA Photon Beam Parameters to date
Photon energy range
Tunability
Polarization
Energy/pulse
Estimated pulse length
Repetition rate
FEL mode
FEL bandwidth
FEL bandwidth
Photon energy fluctuations
FEL bandwidth fluctuations
http://www.elettra.trieste.it/FERMI/index.php?n=Main.Parameter
19‐62 eV (20‐65 nm)
~ 5%
LV/LO/LC/RC
20‐ 30 μJ
<150 fs
10 Hz
TEM00
30‐90 meV n(FWHM)
ΔE/E= 6x10‐4 (rms)
~1.1 meV (rms)
~ 3% (rms)
Wisconsin FEL (WiFEL)
Superconducting L- band
electron linear accelerator
1.7 GeV
SRF
Bunch
gun compressors
0
100
Undulators
2.2 GeV
Experimental
Areas
Beam switchyard
with RF separators
200
300
400
Monochromators
500
600
700 m
•
2.2 GeV CW SC linac with RF separation for many high-rep-rate beamlines
•
Low charge bunches (200 pC)
•
Seeding with High Harmonic Generation sources
•
Cascaded harmonic generation without “fresh bunch”
•
Development of a superconducting cw 200MHz electron gun is underway
NGLS
High rep. rate soft X-ray FEL facility; 2.4 GeV cw s/c linac
o Up to 106 pulses per second
o Seeded
o Ultrashort pulses from 250 as – 250 fs
o Narrow energy bandwidth to 50 meV
o Adjustable photon energy from 280 eV – 1.2 keV
o Polarization control
3 initial beamlines:
Seeded or self-seeded
SASE or self-seeded
2 color seeded
10 μs
≤1 μs
~10–100 fs
5 – 150 fs
5 – 250 fs
0.25 – 25fs
•
•
•
•
•
Up to 100 kHz
High resolution
~Time-bandwidth limited
1011 – 1012 photons/pulse
10-3 – 5x10-5 ∆w/w
• High-resolution spectroscopy
• Diffractive imaging
(with harmonics)
•
•
•
•
•
Up to 100 kHz
Ultra-fast
250 as pulses
Two color
108 ph/pulse
• Multidimensional
X-ray spectroscopy
•
•
•
•
Highest rep rate, MHz
High flux
1011 - 1012 photon/pulse
100 W
• Diffractive imaging
(at highest rate)
• Photon correlation
spectroscopy
NGLS
• LBNL submitted a proposal to
DoE in December 2010
• DOE approved CD-0: “Mission
Need” for a Next Generation Light
Source in April 2011
• Currently no DOE budget to
pursue a Project
• LBNL is
– Performing Accelerator and
Detector R&D
– Performing feasibility studies
which will inform a Conceptual
Design
Users’ Requirements
high pulse energy
transverse coherence
fs pulses (or less)
polarization control
easy tunability
multiple, simultaneous users
high repetition rate
regularly spaced pulses
THz radiation in synchronism with FEL
two-colour FEL pulses
longitudinal coherence / pulse uniformity*
high degree of amplitude stability*
small linewidth*
precise synchronism with lasers for pump-probe expts.
Users’ Requirements
high pulse energy
transverse coherence
fs pulses (or less)
Most requirements not
polarization control
specific to soft X-rays …
easy tunability
multiple, simultaneous users
Especially for soft-X-ray
FELs (?) .. that was the
high repetition rate
view, but now XFEL users
regularly spaced pulses
are starting to demand
THz radiation in synchronism with FEL
such properties
two-colour FEL pulses
longitudinal coherence / pulse uniformity*
high degree of amplitude stability*
small linewidth*
precise synchronism with lasers for pump-probe expts.
Users’ Requirements
high pulse energy
transverse coherence
fs pulses (or less)
polarization control
easy tunability
SASE
multiple, simultaneous users
high repetition rate
regularly spaced pulses
THz radiation in synchronism with FEL
two-colour FEL pulses
longitudinal coherence / pulse uniformity*
Seeded
high degree of amplitude stability*
* or oscillator
small linewidth*
precise synchronism with lasers for pump-probe expts.
Users’ Requirements
high pulse energy
transverse coherence
fs pulses (or less) ……………………………….many different schemes
polarization control …………… APPLE/DELTA/crossed undulator etc.
easy tunability …………………………………… variable gap undulator
multiple, simultaneous users ………… electron switchyard schemes
high repetition rate ………………………………… superconducting RF
regularly spaced pulses ………………………. cw superconducting RF
THz radiation in synchronism with FEL ……………… (pre)/afterburner
two-colour FEL pulses ………………………………..… various schemes
longitudinal coherence / pulse uniformity*
high degree of amplitude stability*
small linewidth*
precise synchronism with lasers for pump-probe expts.
Technical Issues
• Seeding:
- laser sources for shorter wavelength and higher rep. rate
- seeding / modulation / harmonic generation schemes
- modelling thereof
• Electron beam optimisation:
Bunch compression – how many?
Seeded FELs in particular require:
- e- pulse shape control: flat slice parameters  flat gain length
over length of seed pulse + timing jitter; even more for “freshbunch” schemes
- timing jitter reduction due to linac phase and voltage fluctuations
 careful optimisation of gun + linac parameters to meet these
requirements
Technical Issues
• Electron sources
- development of a low emittance, high rep rate injector, is still an
an area of active R&D (see session on Electron Sources)
• Electron beam switching schemes for multiple FELs
- magnetic or RF separation ? tolerances …
• Diagnostics (electron & photon) for low charge, short pulses
In addition, a big issue is COST particularly for high repetition rate FELs,
SCRF technology, especially cw SCRF, is very expensive:
cw SCRF
(NLS, NGLS, WiFEL)
Science
driven
“Cost”
pulsed SCRF
(FLASH, EXFEL)
~ 1 kHz NCRF
currently no
demand, but is
there a “niche” ?
~ 100 Hz NCRF
(LCLS, SACLA, PAL XFEL, SwissFEL etc.)
“Rep. rate”
Given the wavelength range and type of machine,
how to reduce costs ? …… reduce electron beam energy
BUT:
u 
2
K 
1 

n 
2

2 n 
2 
• Shorter period undulators
 higher field
new designs, materials …SCUs ?
 lower gap – what really is the
limit ??
• Higher harmonics
- schemes to enhance harmonic
output (e.g. phase jumps)
- seeding and harmonic
generation schemes
 
N


n
4
Science
driven
• Ultra-low emittance guns
- “conventional” guns at low
charge
- novel electron sources
Could be an interesting
combination.. But
reduced pulse energy ..
Thanks for your attention