Post on 16-Jan-2016
J. Rossbach, DESY1PAC2001
New Developments on Free Electron LasersBased on Self-amplified Spontaneous Emission
J. Rossbach, DESY
Why SASE FELs?
How does it work?
What are the challenges?
Where are we?
Where do we want to go?
J. Rossbach, DESY2PAC2001
Why SASE FELs?
State of the art:Structure of biological macromolecule
Needs 1015 samples
Crystallized not in life environment
reconstructed from diffractionpattern of protein crystal:
LYSOZYME , MW=19,806The crystal lattice imposes restrictions on molecular motion
Images courtesy Janos Hajdu
J. Rossbach, DESY3PAC2001
Why SASE FELs?
SINGLE MACROMOLECULE,Planar section, simulated image
courtesy Janos Hajdu
Resol. does not depend on sample quality
Needs very high radiation power @ 1Å
Can see dynamics if pulse length < 100 fs
J. Rossbach, DESY4PAC2001
We need a radiation source with
• · very high peak and average power• · wavelengths down to atomic scale λ ~ 1Å• · spacially coherent• · monochromatic• · fast tunability in wavelength & timing• · sub-picosecond pulse length
Why SASE FELs?
For wavelengths below ~150 nm: SASE FELs.
J. Rossbach, DESY5PAC2001
How does it work?
Q = Ne·e, Ne = # electrons
Point charge radiates coherently P Ne2 !
Radiation power of oscillating point-like charge Q:
P Q2 2
„Point“ means above all: bunch length < radiation
Synchrotron radiation of an incoherent electron distribution: P Ne
Potential gain in power Ne = 109 – 1010 !!
J. Rossbach, DESY6PAC2001
How does it work?
Coherent motion is all we need !!
J. Rossbach, DESY7PAC2001
How does it work?
Idea: Start with an electron bunch much longer than the desired wavelength and find a mechanism that cuts the beam into equally spaced pieces automatically
Free-Electron Laser (Motz 1950, Phillips ~1960, Madey 1970) Special version: starting from noise (no input needed)
Single pass saturation ( no mirrors needed)
Self-Amplified Spontaneous Emission (SASE)(Kondratenko, Saldin 1980)(Bonifacio, Pellegrini 1984)
J. Rossbach, DESY8PAC2001
How does it work?
laserbeam
undulator electronabsorber
radi
atio
n po
wer o
nlo
garith
mic
scale
lower magnetic poles of the undulator
elektromagnetic wave
electron trajectory
N
S
S
N
S
N
N
S
undulator period U
em
direction of motion
direction of motion
bunch of electronswith increasingdensity modulation
upper
of the undulator
perpendicular tomagnetic field
magnetic poles
Spectrum of amplifiedspontaneous radiation
21
2
2
2
Kuem
Resonance wavelength:
J. Rossbach, DESY9PAC2001
How does it work?
0.05 mm
0.0
5 m
m
Micro-bunching of the X-ray FEL electron beam
FIREFLY microbunching; Ricci,Smith/Stanford
J. Rossbach, DESY10PAC2001
How does it work?
105 by FEL gain
103 by improved beam quality,long undulators
J. Rossbach, DESY11PAC2001
What are the challenges? Overview
Electron beam parameters needed for Self-Amplified-Spontaneous Emission (SASE)
Energy:
für em= 1 Å: E 20 GeV
Energy width:
Narrow resonance E/E ≤ 10-4
Small distortion by wakefields
super conducting linac ideal!
Gain Length:3/1
2
23
0ˆ
2
3
1
IKe
mcL ur
g
21
2
2
2
Kuem
Beam size:
r 40 m high electron desity for
maximum interaction with radiation fieldEmittance ≤ need special electron source to accelerate the beam before it explodes due to Coulomb forces
Peak current inside bunch:Î > 1 kA feasible only at ultrarelativistic energies, otherwise ruins emittance bunch compressor
Straight trajectory in undulator:ultimately < 10 m over 100 m
J. Rossbach, DESY12PAC2001
Why a linear accelerator?
X-ray SASE FEL needs:
energy width σE/E ≤ 10-4
and bunch length σl 25 m (~100 fs)
σE σl 60 eV m
storage ring is limited to >1000 eV melectron emittance ≤ 10-11 m
LEP (20GeV) (!): x > 10-10 m
several kA peak currentwakefields tolerable for single pass, BUT not in storage ring
J. Rossbach, DESY13PAC2001
What are the challenges? RF gun
TESLA FEL photoinjector for small and short electron bunches
J. Rossbach, DESY14PAC2001
What are the challenges? Injector
Layout of integrated injector/compressor for TTF2 and TESLA FEL
J. Rossbach, DESY15PAC2001
What are the challenges? Bunch compression
Section
Bending Magnet Quadrupole Triplett
5 m
Instrumentation
Section
Bending Magnet Quadrupole Triplett
Tail particle, more momentumHead particle, less momentum
magnetische Strahlkompression
Rossbach/DESY
Beware of coherent synchrotron radiation (CSR)Magnetic bunch compression
very powerful microwave radiationwith >~ bunch length if bunch length << size of vacuum chamber
radiation from tail goes straight and can catch up with head of bunch
--> severe beam distortion
Beam dynamics simulation must take into account combined space charge and e.m. radiation in near-field. see: TRAFIC4 by A. Kabel/SLAC
J. Rossbach, DESY16PAC2001
What are the challenges? Bunch compression
rf0
0
2 2
2 sin coss
z y yd s
E
eV
rf0
0
2 2
2 sin coss
z y yd s
E
eV
yy--zz streak streak generated by generated by deflectordeflector
P. Krejcik et. al., P. Krejcik et. al., WPAH116WPAH116P. Krejcik et. al., P. Krejcik et. al., WPAH116WPAH116
P. Emma,P. Emma,J. Frisch,J. Frisch,P. Krejcik,P. Krejcik,G. Loew,G. Loew,X.-J. WangX.-J. Wang
f f = 2856 MHz= 2856 MHzVV00 15 MV 15 MVzz 22 22 mm
f f = 2856 MHz= 2856 MHzVV00 15 MV 15 MVzz 22 22 mm
ee
zz
2.44 m2.44 m
cc pp
90°90°
VV((tt))xx
RFRF‘‘streak’streak’
SS-band-band
Structures built at Structures built at SLACSLAC in in 1960’s 1960’s now installed in now installed in linac for testinglinac for testing
‘‘slice’-slice’- and ‘slice’ energy spread measurements also possible and ‘slice’ energy spread measurements also possible
J. Rossbach, DESY17PAC2001
What are the challenges? Bunch compression
Interferometry of coherent synchrotron radiation
Projection from longitudinal phase space tomography
Longitudinal electron bunch profile at the TESLA Test Facility measured with two different methods
J. Rossbach, DESY18PAC2001
What are the challenges? Bunch compression
Bunch compression down to few 20-30 m is a technical requirement (and complication) to achieve kA peak current for sufficiently small gain length.
It is a lucky coincidence, that the ultra-short pulse length is exactly what users are calling for. From the user point of view, bunch length should be even 10 m !
try harder!
J. Rossbach, DESY19PAC2001
What are the challenges? Wakefields
Wakefields from surface roughness:Test at TTF FEL
Smooth surface
Rough surface, same diameter
E
E
See Markus Hüning, Wed. afternoon
J. Rossbach, DESY20PAC2001
Where are we? Beam parameters
TTF FEL now TESLA FEL
(LCLS similar)
Normalized emittance from gun (Q = 1 nC) 3.5 mrad mm 0.8 mrad mm
Norm. emittance at undulator entrance 8 mrad mm 1.6 mrad mm
Beam size in undulator 100 m 40 m
Bunch length (rms) 1 ps 0.1 ps
Peak current 500 A 5000 A
Long. emittance σE σl 100 eV m 60 eV m
In all key beam parameters, the extrapolation from proven technology is a factor 2 – 10We know what to do and howWe will take further steps at TTF getting even closer to TESLA FEL parameters
J. Rossbach, DESY21PAC2001
Where are we? Progress with SASE FELs: VISA
see:Tremain,MurokhWPPH118/122Wed. afternoon
J. Rossbach, DESY22PAC2001
Where are we? Progress with SASE FELs: LEUTL
J. Rossbach, DESY23PAC2001
Where are we? Progress with SASE FELs: LEUTL
530 nm Energy vs. Distance along the Undulator
Exponential Growth Region
Saturation of SASE
Flash of UV light (385 nm) near saturation. The expected wavelength as a function of angle (radial offset) is clearly seen. The darker “lines” are from shadows of secondary emission monitors in the vacuum chamber.
Stephen Milton/ANLTuesday 13:30h
J. Rossbach, DESY24PAC2001
Where are we? Progress with SASE FELs: TESLA
Phase 1 of the SASE FEL at the TESLA Test Facility at DESY, Hamburg.The total length is 100 m.
J. Rossbach, DESY25PAC2001
Where are we? Progress with SASE FELs: TESLA
TTF FEL undulator
J. Rossbach, DESY26PAC2001
Where are we? Progress with SASE FELs: TESLA
SASEgain>1000
Spontaeous Emission x100
TTF FEL gainat 108 nm vs. bunch charge
By now observedgain >105
J. Rossbach, DESY27PAC2001
Where are we? Progress with SASE FELs: TESLA
J. Rossbach, DESY28PAC2001
Where are we? Progress with SASE FELs: TESLA
FEL wavelengths reached at TTF FEL
J. Rossbach, DESY29PAC2001
Where are we? Progress with SASE FELs: Summary
where wavelength year Livermore ~1 mm 1986LURE/Orsay 5-10 m 1997UCLA/LANL 12 m 1998LEUTL/Argonne 530 nm 1999
385 nm & saturation 2000TTF FEL/DESY 80-180 nm 2000VISA/BNL/LLNL/SLAC/UCLA 845 nm saturation 2001
(+2nd+3rd Harmon.)All observations agree with theoretical expectations/computer models
J. Rossbach, DESY30PAC2001
Where do we want to go?
SASE FEL projects under progress: min. wavelength
APS/LEUTL Phase2 120 nmAPS/LEUTL Phase3 51 nmDESY: TTF FEL Phase2 6 nm 2003/2004SPring8: ~ 5 nm - 2005
SASE FEL projects proposed:
SLAC: LCLS 0.15 nm 2006DESY: TESLA XFEL 0.085 nm 2010
J. Rossbach, DESY31PAC2001
Where do we want to go? Brilliance
Peak brilliance Average brilliance
LCLSmultibunch
LEUTL
TTF FEL
J. Rossbach, DESY32PAC2001
Where do we want to go? LCLS
J. Rossbach, DESY33PAC2001
Where do we want to go? LCLS
SLAC linac tunnel undulator hall
Linac-0L6 m
Linac-1L9 mrf 38°
Linac-2L330 mrf 43°
Linac-3L550 mrf 10°
BC-1L6 m
R56 36 mm
BC-2L24 m
R56 22 mm DL-2L66 mR56 = 0
DL-1L12 mR56 0
undulatorL120 m
7 MeVz 0.83 mm 0.2 %
150 MeVz 0.83 mm 0.10 %
250 MeVz 0.19 mm 1.8 %
4.54 GeVz 0.022 mm 0.76 %
14.35 GeVz 0.022 mm 0.02 %
...existing linac
new
RFgun
25-1a30-8c
21-1b21-1d
21-3b24-6dX
Linac-XL0.6 mrf=
Producing short bunches for LCLS
J. Rossbach, DESY34PAC2001
28 GeV28 GeV
Existing bends compress to Existing bends compress to <100 fsec<100 fsec
~1 Å~1 Å
Add 12-meter chicane compressor Add 12-meter chicane compressor in linac at 1/3-point (9 GeV)in linac at 1/3-point (9 GeV)
Add 12-meter chicane compressor Add 12-meter chicane compressor in linac at 1/3-point (9 GeV)in linac at 1/3-point (9 GeV)
Damping Ring Damping Ring (( 30 30 m)m)
9 ps9 ps 0.4 ps0.4 ps<100 fs<100 fs
50 ps50 ps
SLAC LinacSLAC Linac
1 GeV1 GeV 20-50 GeV20-50 GeV
FFTBFFTBRTL RTL
30 kA30 kA
80 fsec FWHM80 fsec FWHM
1.5%1.5%
Short Bunch Generation in the SLAC LinacShort Bunch Generation in the SLAC Linac
Compress to 80 fsec in 3 stagesCompress to 80 fsec in 3 stages
P. Emma et. al., P. Emma et. al., FPAH165P. Emma et. al., P. Emma et. al., FPAH165
New proposal for:New proposal for: LCLSLCLS accelerator optics R&D accelerator optics R&D Ultra-short Ultra-short xx-ray science -ray science
program at program at SLACSLAC
J. Rossbach, DESY35PAC2001
Where do we want to go? TESLA
TESLA scheme
J. Rossbach, DESY36PAC2001
Where do we want to go? TESLA
Beam switchyard distributing the electron bunch trains to various undulators
J. Rossbach, DESY37PAC2001
Where do we want to go? TESLA
J. Rossbach, DESY38PAC2001
Where do we want to go? TESLA
A potential site for TESLA near Hamburg
J. Rossbach, DESY39PAC2001
Conclusion
SASE FELs clearly demonstrated for wavelengths far below the visible.
Full agreement with theory
User facilities in the VUV/soft X-ray range just around the corner
User facilities in the Angstrøm range are feasible with only moderate extrapolation of present state-of-the-art;Computer simulations and mechanical design are available
Accelerator physics & technology will play major role
Fun guaranteed!