Download - R&D Towards X-ray Free Electron Laser
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R&D TowardsX-ray Free Electron Laser
Li Hua YuBrookhaven National Laboratory
1/23/2004
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SASE
Self Amplified Spontaneous Emission
Saldin et al. (1982)Bonifacio, Pellegrini et al. (1984)
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Gain Length
(Length power increases by a factor of e)
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sn
ss I
,/1,/1 0
Beam quality requirement: Scaling Function of Gain
L.H.Yu, S.Krinsky, R. Gluckstern PRL. 64, 3011 (1990)
),,(DD
GDL
w
s
n
G
w
)1(2
2w
ws a
Wavelength: ( aw ~ 1 )
Emittance (transverse phase space size = beam size*angular spread)
Scaling:
The weak square root scaling is favorable for going to short wavelength
Current I0Electron beam energy γ
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The development of Photocathode RF Gun (R. Schefield, 1985) with Emittance Compensation Solenoid (B.
Carleston) makes it possible to consider high gain X-ray FEL because it provides high brightness beam
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Wavelength λ 1.5 Å Electron energy γ 14.35 GeVNorm. emittance (rms) 1.5 mm mradPeak current I0 3,400 AWiggler Period 3 cmGain Length LG 5.8 m
ww
n
w
LCLS (SLAC) Proposal
Courtesy: Max Cornaccia
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Free-electron laser at DESY delivers highest power at at wavelengths between 13.5 and 13.8 nanometers with an average power of 10 milliwatts and record
energies of up to 170 microjoules per pulse.
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SASE spectrum is not coherent
Train of pulses with independent phase
Spectrum consists spikes
with 100% fluctuation
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High Gain Harmonic Generation (HGHG) for coherence and stability
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HIGH GAIN HARMONIC GENERATION (HGHG)
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DUVFEL Configuration
DUVFEL using NISUS wigglerStep 1. SASE at 400 nmStep 2. direct seeding at 266nmStep 3. HGHG 800nm 266 nm
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Camera image after exit window
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HGHG Experiment
MINI DispersionSection
NISUS
800 nm 266nm
88nm
HGHG from 800 nm266 nm, Output at 266 nm: ~ 120J, e-beam: 300 Amp, 3 mm-mrad, Energy 176MeV
Output at 88 nm ~ 1 JOn-going Experiment Application in Chemistry
L.H.Yu et al PRL 91 074801-1 (2003)
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Spectrum of HGHG and SASE at 266 nm under the same electron beam condition
0.23 nm FWHM
SASE x105
Wavelength (nm)
Inte
nsit
y (a
.u.)
HGHG
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Brookhaven Science Associates
U.S. Department of Energy
I nstallation of the first experiment – Dec, 2002I nstallation of the first experiment – Dec, 2002
Monochromator
Ion Pair Imaging station
Harmonic at 89 nm is used in Ion pair imaging experiment
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CPA (Chirped Pulse Amplification) HGHG Spectra
t
Interpretation of 3 sets of measurements: effect of RF curvature; the second matched e-beam chirp to seed chirp
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1-ST STAGE 2-ND STAGE 3-RD STAGE FINAL AMPLIFIER
AMPLIFIER
w = 6.5 cm
Length = 6 m Lg = 1.3 m
AMPLIFIER
w = 4.2 cm
Length = 8 m Lg = 1.4 m
AMPLIFIER
w = 2.8 cm
Length = 4 m Lg = 1.75 m
MODULATOR
w = 11 cm
Length = 2 m Lg = 1.6 m
MODULATOR
w = 6.5 cm
Length = 2 m Lg = 1.3 m
MODULATOR
w = 4.2 cm
Length = 2 m Lg = 1.4 m
DISPERSION
dd = 1
DISPERSION
dd = 1
DISPERSION
dd = 0.5
DELAY DELAY DELAY“Spent” electrons “Fresh”
electrons“Spent”
electrons
“FRESH BUNCH” CONCEPT
“Fresh” electrons
e- e-
266 nm SEED LASER
53.2 nm2.128
nm10.64 nm5 5 5
400 MW 800 MW 70 MW
1.7 GW
500 MW
A Soft X-Ray Free-Electron Laser
e- e-
LASER PULSE
AMPLIFIER
w = 2.8 cm
Length = 12 m Lg = 1.75 m
R&D Towards Cascading HGHG: One of the Earlier Calculated Schemes
e-beam 750Amp 1mm-mrad
2.6GeV /γ=2×10 – 4 total Lw =36m
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FEL at 1 GeV
FEL at ELETTRA of Trieste
FEL-1 FEL-2
100 40 40 10 nm Wavelength Target
10 31 25 124 eV
Electron Beam Energy 0.70 0.55 1.00 GeV Bunch Charge 1.0 1.0 nC Peak Current 0.8 2.5 kA Bunch Duration (rms) 500 160 fs Energy Spread (rms) 0.5 1.0 MeV Normalized Emittance 2.0 1.5 10-6 m
Undulator Period 52 36.6 mm
FEL -2
electron beam
seeding pulsee.g., 50 fs
2 seednd
wasted part of
the electron beam
HGHG output
M1S
U1 M2 U2
0/5
2
~ 10 nm
0/5
~ 50 nm
0/5
~ 50 nm
0
~ 250 nm
electron beam
FEL output
synchoronized
seeding pulse
0
-
electron beam
seeding pulsee.g., 50 fs
2 seednd
wasted part of
the electron beam
HGHG output
M1S
U1 M2 U2
0/5
2
~ 10 nm
0/5
~ 50 nm
0/5
~ 50 nm
0
~ 250 nm
electron beam
FEL output
synchoronized
seeding pulse
0
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Introduction
Coherent time:
fskT 100/
•Ultrahigh Spatial Resolution •Microscopy •Coherent X-ray Scattering
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is electron energy
S
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2
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•Angular spread also degrades micro-bunching
•Strong focusing reduces beam size but increases angular spread
•Emittance
~ beam size×angular spread
•Requirement on : 4S
Emittance
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0.01 0.02 0.05 0.1 0.2 0.5 1 2
0.2
0.4
0.6
0.8
0.01 0.02 0.05 0.1 0.2 0.5 1 2
s2
G
1.0D
0.01 0.02 0.05 0.1 0.2 0.5 1 2
0.2
0.4
0.6
0.8
0.01 0.02 0.05 0.1 0.2 0.5 1 2
2.0D
s2
G
1. 0.5 0.15 0.08 0.03
Dk
k
w
Scaled Focusing DUV(BNL)(100nm)
TTF (DESY)(6nm)
LCLS(SLAC)(0.15nm)
0.01 0.02 0.05 0.1 0.2 0.5 1 2
0.2
0.4
0.6
0.8
0.01 0.02 0.05 0.1 0.2 0.5 1 2
Scaled Emittance
Scaled Energy Spread
s2
04.0D
G
On the scaled function plot, operating points do not change very much even though wavelength changes several orders of magnitudes
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Single shot and average SASE spectrum
showing fluctuation and spikes
A series of SASE experiment confirming the Theory
Schematic of DESY SASE experiment at 100 nm
•LANL, UCLA: 15 m (1999)
•APS: Luetle 0.4 m (2000-2001)
•BNL, SLAC, UCLA: 0.8 m (2001)
•DESY: 0.1 m (2002)
•BNL: UVFEL 0.266 m (2002)
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Deep UV Free Electron Laser at SDL
A d ju stab leC h ican e
1 7 7M eV
R F ze roP h a sin gP h o to in jec to rC T R M o n ito r
N o rm a l in c id en ce
7 7 M eV
F E L seeda t 8 0 0 n m
M o d u la to r U n d u la to r
N IS U S p o p -inm o n ito rs
F E L M ea su re m en tE n e rg y, S p e c tru m , S y n ch ro n iza tio nan d P u lse L e n g th M easu rem e n tsa t 2 6 6 n m
s
Io n P a ir Im ag in gE x p e rim en ta t 8 8 n m
N isu s W ig g le r
3 0 m J T i:S ap p h ireA m p lifie r
D isp e rs io nM ag n e t T rim C h ican e
Seed 9ps
Cathode driver 4 ps
Uncompressed bunch 4-5ps
Compressed 1ps
Relation of pulse lengths
During 2002-2003 operation
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NISUS Undulator Parameters
• Period λw= 3.9 cm
• Length 10 m
• Canted poles provide horizontal focusing and reduce vertical focusing
• 4-wire focusing provide tuning ability to reach equal focusing Natural focusing: betatron wavelength λβ=20 m
• Because focusing is not strong, also because period 3.9 cm is large, gain length is far from optimized.
FEL gain length• Simulation: HGHG reaches saturation at 400 nm with current
I0= 300 amp, emittance εn= 5 mm-mrad, energy spread
σγ / γ =1.510-3, gain length LG=1.1 m
• We do not expect SASE saturation, because we have only 10 gain length
• SASE in February 2002 : LG=0.9 m
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Two sets of data compared with Simulation
current 300 Amp, energy spread 110 –4, dispersion dd = 8.7
(a) 12/11/02 Model: Pin=1.8MW pulse length 0.6 ps, slice emittance 2.7 mm-mrad
(b) 3/19/03 Model: Pin=30MW pulse length 1 ps, projected emittance 4.7 mm-mrad
Whole bunch contributes to the output
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Autocorrelation Pulse Length Measurement
current 300 Amp, energy spread 110 –4, dispersion dd = 8.7
(a) 12/11/02 Model: Pin=1.8MW pulse length 0.6 ps, slice emittance 2.7 mm-mrad
(b) 3/19/03 Model: Pin=30MW pulse length 1 ps, projected emittance 4.7 mm-mrad
Whole bunch contributes to the output
(a) (b)
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If NISUS were increased to 20 m, the SASE
would be saturated. The gray line is a Genesis
Simulation.
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0.35nm
22
8
2661
0.64 0.64 3 10 / 0.35b
nmT ps
c m s nm
Average spacing between peaks in SASE spectrum also gives pulse length 1ps
S.Krinsky (2001)
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22
8
2660.23
1 3 10 /
nmnm
c ps m s
0.23 nm FWHMSASE x105
Wavelength (nm)
Inte
nsit
y (a
.u.) HGHG
For a flat-top 1ps pulse the bandwidth is
HGHG output is nearly Fourier transform limited
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SASE
HGHG
Shot to Shot Intensity Fluctuation
Shows High Stability of HGHG output
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Chirped and Unchirped HGHG spectra
SASE spectrumHGHG spectrum no chirpCPA HGHG ~1 MeVCPA HGHG ~2 MeVCPA HGHG ~3 MeV
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Bandwidth vs ChirpBandwidth vs Chirp
Seed bandwidth is 5.5 nm currently, thus 1.8 nm is expected at third harmonic.
Spectrum at /%
1.5nm
1.8nm
1/3 BW of seed
/(%)
FW
HM
Ban
dwid
th
(nm
)
• Next: measurement of phase distortion
• CPA: expected pulse length > 50fs (B. Sheehy, Z. Wu)
• R&D: CPA at 100 nm?
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Measuring the spectral phase: SPIDER(Spectral Interferometry for Direct Electric-Field Reconstruction)
(Walmsley group, Oxford)
800 nm
266 nm
400 nm
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Spidering a laboratory 266 nm source (B. Sheehy, Z. Wu_)
-0.05 0 0.05-10
0
10
20
30
- 0 (PHz)
rad
ian
s
amplitudephasefit chirpphase-chirp
-0.05 0 0.050
0.2
0.4
0.6
0.8
1
- 0 (PHz)
inte
nsi
ty (
arb
un
its)
Typical Spider Trace
Reconstructed phase and amplitude Comparison with x-correlation
•Undercompress a 100 femtosecond 800 nm Ti:Sapph chirped-pulse-amplification system• Frequency-triple in BBO to 266 nm(spoil phase matching to create an asymmetry in the time profile)• Compare scanning multi-shot x-correlation of the 266 nm and a short 800 nm pulse with the average reconstruction, convolved with 250 fsec resolution of the x-correlator
-1 -0.5 0 0.5 1 1.50
0.2
0.4
0.6
0.8
1
time (psec)
inte
nsi
ty (
arb
un
its)
spidercross correlation
900 fsec FWHM
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-1500 -1000 -500 0 500 1000 1500-8
-6
-4
-2
0
2
4
6
8pulse shape and phase in time domain
fs
phas
e (r
adia
ns)
Time (fs)
Pha
se (
Rad
ian)
Preliminary Data of SPIDER for a chirped HGHGPhase and amplitude vs. time
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-2000 -1500 -1000 -500 0 500 1000 1500 2000-5
-4
-3
-2
-1
0
1
2
3
4
5x 10
-3 instantaneous frequency
fs
f-f0
(P
Hz)
Preliminary Data of SPIDER for a chirped HGHGFrequency change vs. time (electron beam energy chirp unmatched )
Time (fs)
(T
Hz) Theory based
on measured seed chirp
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Before Shifter After Shifter
Electron
bunchLaser
pulse
Fresh Bunch Technique
Technical issues:
•Time jitter of seed << electron bunch length
•Reduce number of stages: higher harmonic, smaller local energy spread
•Shorter seed laser pulse
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Energy Upgrade for 100 nm Output8’th Harmonic Generation
MINI DispersionSection
NISUS
8000( Å ) 1000( Å )
333(Å)
HGHG from 800 nm100 nm, Output at 100 nm: ~0.1mJ, e-beam: 300 Amp, 3 mm-mrad, Linac Upgrade: Energy 300MeV
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Cascading HGHG for Shorter Wavelength
e-beam600Amp250 MeV2.7 mm-mrad / = 1.×10 - 4
Pin=1.5 MW
266nm 66.5 nm
Pout=140 MW56 MW
133nm
2m VISA
6 m NISUS0.8m MINI
Pulse length ~ 0.5ps 70J Range: 50 nm—100nm