Transcript Slide 1

Seeding for Fully Coherent Beams
William S. Graves
MIT-Bates
Presented at MIT x-ray laser
ASAC committee review
Sept 18-19, 2003
W.S. Graves
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Bandwidth and Pulse Length
Seeded beam
SASE beam
Output
wavelength
FEL param
rFEL
Dtmin (fs) at
max BW
DEmin (meV) at
1 ps FWHM
SASE Dtmin
(fs)
SASE DEmin
(meV)
100 nm
9.e-3
20
2
100
110
10 nm
4.e-3
5
2
100
500
1 nm
1.5e-3
1
2
100
1900
0.1 nm
0.2e-3
0.8
2
100
2500
Seeded beams limited only by uncertainty principle
Df Dt 
and seed properties.
SASE properties determined by ebeam.
W.S. Graves
Df
f
1
2
 rFEL
2
Master oscillator
Seed
laser
UV Hall
Fiber link synchronization
Pump
laser
Seed
laser
X-ray Hall
Pump
laser
Undulators
100 nm
Injector
laser
30 nm
Undulators
1 nm
10 nm
0.3 nm
SC Linac
1 GeV
2 GeV
4 GeV
10 nm
3 nm
1 nm
Undulators
Seed
laser
W.S. Graves
Nanometer Hall
Pump
laser
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High Gain Harmonic Generation
Method to reach short wavelength FEL output
from longer wavelength input seed laser.
Input seed at w0
overlaps electron
beam in energy
modulator undulator.
Energy modulation is
converted to spatial
bunching in chicane
magnets.
Modulator is tuned
to w0.
5th harmonic
bunching is
optimized in
chicane.
Electron beam
develops energy
modulation at w0.
W.S. Graves
Electron beam radiates
coherently at 5w0 in long
radiator undulator.
Radiator is tuned to 5w0.
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Single stage HGHG
Seed with low harmonic of
conventional laser at 200 – 266 nm,
Single HGHG section
or HHG at 50 – 5 nm.
FEL output at 1st – 5th
harmonic at 200 – 40 nm,
or 50 – 1 nm from HHG.
Modulator Dispersion
Radiator
Use for seeding near final wavelength.
Can seed with either short (~10 fs) or long (1 ps) pulse.
Ebeam should be matched to needs…0.2 nC for short
pulse, 1.0 nC for long pulse.
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Data from BNL’s DUV-FEL experiment
L.-H. Yu et al, Phys. Rev. Lett. 91.074801, Aug. 2003
HGHG and SASE spectra
Measured data and simulations
at 3rd harmonic of seed
of HGHG for 2 input seed
wavelength (800 nm).
power levels.
•Experiment confirms transform-limited spectral width.
•Illustrates modest SASE background from short undulators.
W.S. Graves
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HGHG FEL Simulation
•Use code GINGER.
•Multidimensional, time dependent, polychromatic.
•Model full HGHG cascade: radiation field and electron distribution are
passed from stage to stage.
•Includes electron beam shot noise and SASE effects. Accurately
models frequency dependence of noise amplification.
•Some optimization done. Still far to go…
Code author W. Fawley of LBNL contributed much to these simulations.
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HGHG FEL Simulation
Physics not yet included in model
•Full magnetic lattice. Code now assumes uniform constant focusing.
•Effect of alignment errors, beam mismatch, undulator errors.
•Second order matrix elements in HGHG dispersion sections.
•Noise in input seed.
•Optical transport and matching between sections.
•No sensitivity studies yet.
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Cascaded HGHG
Input
seed w0
Stage 1 output at
Stage 2 output at
…Nth stage
5w0 seeds 2nd stage
25w0 seeds 3rd stage
output at 5Nw0
1st stage
2nd stage
…Nth stage
•Factor of ~30 in wavelength is reasonable without additional
acceleration between stages.
•Seed longer wavelength (100 – 10 nm) beamlines with ~200 nm harmonic
from synchronized Ti:Sapp laser.
•Seed shorter wavelength (50 – 0.3 nm) beamlines with HHG pulses.
W.S. Graves
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2-stage HGHG cascade with single electron bunch
HGHG output
Disturbed
Short seed
e-beam
pulse
pulse
Disturbed
e-beam
Chicane
Electron
delay line
bunch
Mod A Disp A
Rad A
Mod B Disp B
Rad B
Monochromator,
focusing element, etc
•Appropriate for very short seed pulses.
•Undulators are short enough that SASE is insignificant.
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Example: Short pulse 8 nm seed, 0.32 nm output
HGHG parameters
Undulator Parameters for Short Pulse Seed
lw (cm)
l0 (nm)
4.3
5.0
8.0
3.4
Radiator A
2.3
3.1
1.6
7.5
1.5
Modulator B
2.3
3.1
1.6
0.4
8
1.6
Radiator B
1.1
1.8
0.32
16.0
Disp. A
Disp. B
R56 (mm)
6.5
0.7
Charge
Bunching
.08
.04
Peak current
Mod. A
Mod. B
aw
Dgin
0.8
0.8
Modulator A
Pin (MW)
10
1600
Dgout
1.5
l (nm)
Lw (m)
Beam Parameters for Short Pulse Seed
0.2
nC
1000
A
Slice emittance
0.6
mm
Slice energy spread
0.4
MeV
Ebeam energy
4.0
GeV
Rad. A
Rad. B
Dgin
1.5
1.5
Dgout
0.36
0.45
RMS Seed pulse length
1
fs
Pout (MW)
1600
2800
Seed wavelength
8
nm
l (nm)
1.6
0.32
Seed power
5
MW
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2-stage, short pulse HGHG simulation output
Rad. A output at 1.6 nm
HHG seed at 8 nm
Rad. B output at 0.32 nm
3000
st = 1.0 fs
3000
st = 0.66 fs
6
4
2
2000
1500
1000
2000
1500
1000
500
-3
-2
-1
0
1
2
3
0
-4
4
Linear plots of time
profiles and spectra
of HGHG output from
radiators A and B.
-3
-2
-1
0
1
2
3
-3
-2
-1
1
0.8
0.8
0.6
0.4
0.2
Wavelength (nm)
0
1
2
3
4
Time (fs)
1
0
1.594 1.596 1.598 1.6 1.602 1.604 1.606
W.S. Graves
0
-4
4
Time (fs)
Intensity (A.U.)
Time (fs)
500
Intensity (A.U.)
0
-4
st = 0.64 fs
2500
Power (MW)
2500
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Power (MW)
Power (MW)
10
0.6
0.4
0.2
0
0.319
0.3195
0.32
0.3205
0.321
Wavelength (nm)
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2-stage, short pulse HGHG output time profiles
Seed at 8 nm. Output at 5th and 25th harmonics from radiators A and B respectively.
1.6 nm
0.32 nm
Growth of SASE background is apparent at short wavelength.
Due to long undulator, amplification of initial noise.
W.S. Graves
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2-stage, short pulse HGHG output spectra
1.6 nm
W.S. Graves
0.32 nm
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3rd harmonic bunching at 0.1 nm
Near saturation, 3rd harmonic
bunching reaches 8%, producing
substantial radiation (1 mJ) at 0.1
nm from radiator B.
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2-stage, long pulse HGHG cascade
Uses 2 electron bunches.
No fast switch required.
After delay line, leading pulse is
seeded by radiator A output.
Seed trailing
e-beam
Unseeded
e-beam
HGHG section A
Monochromator,
focusing element, etc
W.S. Graves
HGHG section B
0.77 or 1.54 ns
delay line
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Example: 2-stage, long pulse HGHG cascade
Seed wavelength = 200 nm
Rad. B output at 1.6 nm
Rad. A output at 40 nm
2000
Charge
1.0
nC
1000
A
Slice emittance
1.0
mm
Slice dE/E
0.4
MeV
Ebeam energy
1.0
GeV
RMS Seed pulse
length
1
ps
Seed wavelength
200
Seed power
130
Peak current
st = 0.66 fs
1500
Power (MW)
Beam Parameters for Long Pulse
Seed
Power (MW)
2000
1000
500
0
-0.4
-0.2
0
0.2
0.4
1000
500
0
-0.4
-0.2
0
0.2
Time (fs)
Time (fs)
1
1
0.8
0.8
nm
0.6
0.6
MW
0.4
0.4
0.2
0.2
0
39.9
39.95
40
40.05
Wavelength (nm)
Df/frms = 8×10-5
W.S. Graves
0.6
st = 0.64 fs
1500
0
7.99
0.4
0.6
7.995
8
8.005
Wavelength (nm)
8.01
Df/frms = 4×10-5
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RF deflector for seeding at different energies
Dipole
Quad
Quad
Acc.
Acc.
Cavity
1 GeV
Septum
1 GeV
1.3 GHz accelerating freq
0.7 ns
to 4 GeV
to 4 GeV
0.65 GHz deflecting freq
At 1 GeV pulses are separated by sub-harmonic RF deflector
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4-stage, long pulse HGHG cascade
Uses 4 electron bunches.
2 at 1 GeV and 2 bunches at 4 GeV.
40 nm
HGHG
section A
8 nm
Delay
1 GeV
W.S. Graves
HGHG
section B
1.6 nm
HGHG
section C
.32 nm
Delay
HGHG
section D
4 GeV
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4-stage, long pulse HGHG cascade parameters
Modulator A
Modulator B
Modulator C
Modulator D
Dgin
0.2
0.2
0.2
0.2
Pin (MW)
130
1100
850
1700
Dgout
0.42
0.55
0.60
0.65
l (nm)
200
40
8.0
1.6
Dispersion A
Dispersion B
Dispersion C
Dispersion D
R56 (mm)
86.7
15.6
4.2
2.65
dq/dg
6.9
6.3
6.2
6.6
Bunching
0.08
0.06
0.08
0.04
Radiator A
Radiator B
Radiator C
Radiator D
Dgin
0.42
0.55
0.60
0.65
Pin (MW)
0
0
0
0
Dgout
5.0
3.5
7.0
6.5
Pout (MW)
1100
850
1700
450
l (nm)
40
8.0
1.6
0.32
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4-stage, long pulse HGHG cascade parameters
Undulator Parameters for Narrow Bandwidth Seed
aw
lw (cm)
l0 (nm)
Lw (m)
Beam Parameters for Narrow
Bandwidth Seed
Modulator A
5.4
5.0
200
0.1
Charge
Radiator A
3.0
3.1
40
3.6
Peak current
Modulator B
3.0
3.1
40
0.1
Radiator B
1.6
1.8
8
Modulator C
4.3
5.0
Radiator C
2.3
Modulator D
Radiator D
W.S. Graves
1
nC
1000
A
Slice emittance
1.0
mm
3.8
Slice dE/E
0.2
MeV
8
0.45
Ebeam energy
1.0 / 4.0
GeV
3.1
1.6
8.0
1
ps
2.3
3.1
1.6
0.25
Seed pulse
length
1.1
1.8
0.32
22.0
Seed l0
200
nm
Seed power
500
MW
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4-stage, long pulse HGHG cascade output
2000
1000
500
0
-0.4
-0.2
0
0.2
0.4
0.6
2000
8 nm
1500
Power (MW)
40 nm
1500
Power (MW)
Power (MW)
2000
2 stages at 4 GeV
1000
500
0
-0.4
-0.2
Time (ps)
0
0.2
0.4
0.6
1000
500
0
1
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
40
40.05
Wavelength (nm)
W.S. Graves
0
7.99
7.995
8
600
400
-0.4
-0.2
0
0.2
0.4
0.6
0
-0.4
-0.2
Time (ps)
1
39.95
.32 nm
800
200
Time (ps)
1
0
39.9
1.6 nm
1500
1000
Power (MW)
2 stages at 1 GeV
8.005
8.01
0
1.595
Wavelength (nm)
0
0.2
0.4
Time (ps)
1
0.8
0.6
0.4
0.2
1.6
Wavelength (nm)
l0 (nm)
st (fs)
RMS Df/f
Radiator A
40
150
8E-5
Radiator B
8
100
4E-5
Radiator C
1.6
70
5E-5
Radiator D
0.32
80
6E-5
1.605
0
0.3198
0.3199
0.32
0.3201
Wavelength (nm)
22
0.6
Low-gain harmonic generation
8 m long undulator for 1.6 nm radiator
Fawley suggests may have better
noise immunity by performing
frequency multiplication with CSE
of bunched beam.
Avoid exponential gain in
intermediate stages.
Coherent
spontaneous
emission
W.S. Graves
Exponential
gain
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Source comparison
APS
MIT Bates
Und. A
SASE FEL
Min
bandwidth
seeded FEL
X-rays per pulse
(0.1% max BW)
1.E+08
3.E+11
3.E+11
6.E+09
Peak brilliance
(p/s/0.1%/mm2)
3.E+22
1.E+33
3.E+35
7.E+33
Peak flux (p/s/0.1%)
1.E+18
6.E+24
6.E+24
1.E+23
Avg. flux (p/s/0.1%)
7.E+14
3.E+14
3.E+14
6.E+12
Average brilliance
(p/s/0.1%/mm2)
4.E+19
5.E+22
1.E+25
3.E+23
0.1
4.E+09
3.E+11
6.E+09
73000
100
100
1
Degeneracy parameter
Pulse length (fs)
Photon beamlines
34
10-30
Wavelength (nm)
0.05 - .4
0.3 - 100
Pulse frequency (Hz)
7.E+06
1000
W.S. Graves
Min
pulse length
seeded FEL
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Summary
•GINGER is a powerful tool to model HGHG cascades.
•Production of sub-fs pulses by seeding with HHG looks promising.
•Narrow bandwidth seeding shows potential…needs more work.
•Undulator configurations vary for different goals. Will limit options on given beamline.
Next steps
1. Test performance sensitivity to input parameter variation and errors.
2. Add missing physics: optical transport, lattice, real dispersion sections.
3. Reduce noise effects through cascade…test LGHG.
4. Optimize.
W.S. Graves
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Nanometer Hall
to master oscillator for timing sync
Direct seeded or cascaded
HGHG undulators
10 nm
Ti:Sapp + BBO = 200
nm seed
Ti:Sapp + HHG = 10-30 nm seed
Tune by OPA or harmonic number
Seed
lasers
~20 m length
Pump
lasers
10 GW peak
Cascaded HGHG undulators
3 nm
Cascaded HGHG undulators
Ti:Sapp + HHG = 10-30 nm seed
1 nm
Tune by OPA or harmonic number
~30 m length
4 GW peak
W.S. Graves
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